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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933
(No. 002-34393)	þ
Pre- Effective Amendment No. ____	o
Post-Effective Amendment No. 181	þ

and/or

REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY ACT OF 1940
(No. 811-01879)	þ
Amendment No. 164	þ

(Check appropriate box or boxes.)

JANUS INVESTMENT FUND

(Exact Name of Registrant as Specified in Charter)

151 Detroit Street, Denver, Colorado 80206-4805

(Address of Principal Executive Offices) (Zip Code)

Registrant’s Telephone Number, including Area Code: 303-333-3863

Stephanie Grauerholz-Lofton — 151 Detroit Street, Denver, Colorado 80206-4805

(Name and Address of Agent for Service)

Approximate Date of Proposed Public Offering: As soon as practicable after the effective date of this Registration Statement and thereafter from day to day.

It is proposed that this filing will become effective (check appropriate box):

þ     immediately upon filing pursuant to paragraph (b)

o     on (date) pursuant to paragraph (b)

o     60 days after filing pursuant to paragraph (a)(1)

o     on (date) pursuant to paragraph (a)(1)

o     75 days after filing pursuant to paragraph (a)(2)

o     on (date) pursuant to paragraph (a)(2) of rule 485.

If appropriate, check the following box:

o      This post-effective amendment designates a new effective date for a previously filed post-effective amendment.

SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933, as amended, and the Investment Company Act of 1940, as amended, the Registrant certifies that it meets all of the requirements for effectiveness of this Amendment to its Registration Statement pursuant to Rule 485(b) under the Securities Act of 1933, as amended, and has duly caused this Amendment to its Registration Statement to be signed on its behalf by the undersigned, thereto duly authorized, in the City of Denver, and State of Colorado, on the 19^th day of November, 2012.

JANUS INVESTMENT FUND
By:	/s/ Robin C. Beery
	Robin C. Beery, President and Chief Executive Officer

     Janus Investment Fund is organized under an Amended and Restated Agreement and Declaration of Trust dated March 18, 2003 (“Declaration of Trust”), a copy of which is on file with the Secretary of State of The Commonwealth of Massachusetts. The obligations of the Registrant hereunder are not binding upon any of the Trustees, shareholders, nominees, officers, agents or employees of the Registrant personally, but bind only the trust property of the Registrant, as provided in the Declaration of Trust of the Registrant. The execution of this Amendment to the Registration Statement has been authorized by the Trustees of the Registrant and this Amendment to the Registration Statement has been signed by an authorized officer of the Registrant, acting as such, and neither such authorization by such Trustees nor such execution by such officer shall be deemed to have been made by any of them personally, but shall bind only the trust property of the Registrant as provided in its Declaration of Trust.

     Pursuant to the requirements of the Securities Act of 1933, as amended, this Amendment to the Registration Statement has been signed below by the following persons in the capacities and on the dates indicated.

Signature	Title	Date
/s/ Robin C. Beery Robin C. Beery	President and Chief Executive Officer (Principal Executive Officer)	November 19, 2012
/s/ Jesper Nergaard Jesper Nergaard	Vice President, Chief Financial Officer, Treasurer and Principal Accounting Officer (Principal Financial Officer and Principal Accounting Officer)	November 19, 2012

C-1

Signature	Title	Date
William F. McCalpin* William F. McCalpin	Chairman and Trustee	November 19, 2012
William D. Cvengros* William D. Cvengros	Trustee	November 19, 2012
John P. McGonigle* John P. McGonigle	Trustee	November 19, 2012
James T. Rothe* James T. Rothe	Trustee	November 19, 2012
William D. Stewart* William D. Stewart	Trustee	November 19, 2012
Linda S. Wolf* Linda S. Wolf	Trustee	November 19, 2012

/s/ Stephanie Grauerholz-Lofton
`
*By:	Stephanie Grauerholz-Lofton
	Attorney-in-Fact
	Pursuant to Powers of Attorney, dated April 11, 2008, incorporated by reference to Exhibit 15(c) to Post-Effective Amendment No. 123, filed on February 27, 2009; Power of Attorney, dated June 24, 2010, incorporated by reference to Exhibit (q)(4) to Post-Effective Amendment No. 132, filed on July 30, 2010; and Power of Attorney, dated January 5, 2011, incorporated by reference to Exhibit (q)(5) to Post-Effective Amendment No. 138, filed on January 28, 2011

C-2

INDEX OF EXHIBITS

Exhibit Number	Exhibit Title
EX-101.INS	XBRL Instance Document
EX-101.SCH	XBRL Taxonomy Extension Schema Document
EX-101.CAL	XBRL Taxonomy Extension Calculation Linkbase
EX-101.LAB	XBRL Taxonomy Extension Labels Linkbase
EX-101.PRE	XBRL Taxonomy Extension Presentation Linkbase
EX-101.DEF	XBRL Taxonomy Extension Definition Linkbase

C-3

XML

INTECH Global Dividend Fund | Class A, C, S, I, T Shares

Fund summary

INTECH Global Dividend Fund

INVESTMENT OBJECTIVE

INTECH Global Dividend Fund seeks long-term growth of capital and income.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 46 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.

SHAREHOLDER FEES
(fees paid directly from your investment)

Shareholder Fees INTECH Global Dividend Fund Class A, C, S, I, T Shares

Class A

Class C

Class S

Class I

Class T

Shareholder Fees Column [Text]

Class A

Class C

Class S

Class I

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

5.75%

none

none

none

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

none

1.00%

none

none

none

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses INTECH Global Dividend Fund Class A, C, S, I, T Shares

Class A

Class C

Class S

Class I

Class T

Operating Expenses Column [Text]

Class A

Class C

Class S

Class I

Class T

Management Fees

0.55%

0.55%

0.55%

0.55%

0.55%

Distribution/Service (12b-1) Fees

0.25%

1.00%

0.25%

none

none

Other Expenses

4.78%

4.78%

5.04%

4.52%

4.98%

Total Annual Fund Operating Expenses

^[1]

5.58%

6.33%

5.84%

5.07%

5.53%

Fee Waiver

^[1]

4.81%

4.81%

4.82%

4.55%

4.76%

Total Annual Fund Operating Expenses After Fee Waiver

^[1]

0.77%

1.52%

1.02%

0.52%

0.77%

EXAMPLE:

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers or recoupments (if applicable) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

If Shares are redeemed:

Expense Example INTECH Global Dividend Fund Class A, C, S, I, T Shares (USD $)

Expense Example, By Year, Column [Text]

1 Year

3 Years

5 Years

10 Years

Class A

Class A Shares

1,099

2,139

3,167

5,684

Class C

Class C Shares

729

1,861

3,061

5,925

Class S

Class S Shares

582

1,730

2,859

5,600

Class I

Class I Shares

507

1,519

2,531

5,052

Class T

Class T Shares

552

1,646

2,729

5,386

If Shares are not redeemed:

Expense Example, No Redemption INTECH Global Dividend Fund Class A, C, S, I, T Shares (USD $)

Expense Example, No Redemption, By Year, Column [Text]

1 Year

3 Years

5 Years

10 Years

Class A

Class A Shares

1,099

2,139

3,167

5,684

Class C

Class C Shares

629

1,861

3,061

5,925

Class S

Class S Shares

582

1,730

2,859

5,600

Class I

Class I Shares

507

1,519

2,531

5,052

Class T

Class T Shares

552

1,646

2,729

5,386

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the period December 15, 2011 to June 30, 2012, the Fund’s portfolio turnover rate was 24% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund invests, under normal circumstances, at least 80% of its net assets in dividend-paying securities. The Fund invests primarily in common stocks from the universe of the Morgan Stanley Capital International (“MSCI”) World High Dividend Yield Index, utilizing INTECH’s mathematical investment process. The MSCI World High Dividend Yield Index is designed to reflect the performance of the high dividend yield securities contained within the broader MSCI World Index^sm. The Fund may also invest in foreign equity and debt securities.

The Fund pursues its investment objective by applying a mathematical investment process to construct an investment portfolio from the universe of common stocks within its named benchmark index. The goal of this process is to build a portfolio of stocks in a more efficient combination than the named benchmark index. The process seeks to capitalize on the natural volatility of the market by searching for stocks within the index that have high relative volatility (providing the potential for excess returns) but that essentially move in opposite directions or have low correlation to each other (providing the potential for lower relative risk). By constructing the portfolio in this manner and periodically rebalancing the portfolio to maintain potentially more efficient weightings, INTECH’s mathematical investment process seeks to create a portfolio that, over time, produces returns in excess of its named benchmark index with risks similar to that of the benchmark index. The rebalancing techniques used by INTECH may result in a higher portfolio turnover compared to a “buy and hold” fund strategy.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Foreign Exposure Risk. The Fund normally has significant exposure to foreign markets as a result of its investments in foreign securities, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio.

Dividend Risk. Companies that issue dividend-yielding securities are not required to continue to pay dividends on such securities. Therefore, there is the possibility that such companies could reduce or eliminate the payment of dividends in the future.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Investment Process Risk. The proprietary mathematical investment process used by INTECH may not achieve the desired results. On an occasional basis, INTECH considers changes to its mathematical investment process. These changes may result in changes to the portfolio, might not provide the intended results, and may adversely impact the Fund’s performance.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The Fund does not have a full calendar year of operations. Performance information for certain periods is included in the Fund’s first annual and/or semiannual report.

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, and Class S Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 0.50% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees. For a period of three years subsequent to the Fund's commencement of operations (December 15, 2011), Janus Capital may recover from the Fund fees and expenses previously waived or reimbursed, which could then be considered a deferral, if the Fund's expense ratio, including recovered expenses, falls below the expense limit.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Perkins Mid Cap Value Fund | Class D Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Perkins Mid Cap Value Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Perkins Mid Cap Value Fund seeks capital appreciation.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 54% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

54.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund pursues its investment objective by investing primarily in common stocks selected for their capital appreciation potential. The Fund primarily invests in the common stocks of mid-sized companies whose stock prices the portfolio managers believe to be undervalued. The Fund invests, under normal circumstances, at least 80% of its net assets in equity securities of companies whose market capitalization falls, at the time of purchase, within the 12-month average of the capitalization range of the Russell Midcap^® Value Index. This average is updated monthly. The market capitalizations within the index will vary, but as of June 30, 2012, they ranged from approximately $1.3 billion to $18.5 billion. The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets. The Fund may invest, under normal circumstances, up to 20% of its net assets in securities of companies having market capitalizations outside of the aforementioned market capitalization ranges. In addition, when the portfolio managers believe that market conditions are unfavorable for investing, or when they are otherwise unable to locate attractive investment opportunities, the Fund may invest up to 20% of its net assets in cash or similar investments.

The Fund focuses on companies that have fallen out of favor with the market or that appear to be temporarily misunderstood by the investment community. The Fund’s portfolio managers generally look for companies with:

•  strong balance sheets and solid recurring free cash flows
•  attractive relative and absolute valuation ratios or that have underperformed recently
•  favorable reward to risk characteristics

The Fund may also invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. The Fund has and is expected to continue to buy and sell put and call options, particularly on market indices, for hedging purposes (to offset risks associated with an investment, currency exposure, or market conditions) and to enhance returns. The Fund’s exposure to derivatives will vary, is not limited to those derivatives listed, and could be significant at times. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s portfolio managers. When the Fund’s investments in cash or similar investments increase due to a lack of favorable investment opportunities or other extraordinary factors, the Fund may not participate in market advances or declines to the same extent that it would if the Fund had been fully invested.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Mid-Sized Companies Risk. The Fund’s investments in securities issued by mid-sized companies may involve greater risks than are customarily associated with larger, more established companies. Securities issued by mid-sized companies tend to be more volatile than securities issued by larger or more established companies and may underperform as compared to the securities of larger companies.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

The biggest risk is that the Fund’s returns will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares (formerly named Investor Shares). For the periods prior to April 21, 2003, the performance shown for Class D Shares reflects the historical performance of Berger Mid Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Mid Cap Value Fund – Investor Shares into the Fund’s Class J Shares). If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-800-525-3713

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/allfunds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class D Shares (calendar year-end)

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Second Quarter 2003  17.17%          Worst Quarter:  Fourth Quarter 2008  −19.63%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 9.11%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; for the Fund’s Class J Shares (formerly named Investor Shares) for the period April 21, 2003 to February 16, 2010; and for Berger Mid Cap Value Fund – Investor Shares for periods prior to April 21, 2003. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Perkins Mid Cap Value Fund | Class D Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class D

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.54%

Other Expenses

rr_OtherExpensesOverAssets

0.20%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.74%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class D Shares

1 Year

rr_ExpenseExampleYear01

76

3 Years

rr_ExpenseExampleYear03

237

5 Years

rr_ExpenseExampleYear05

411

10 Years

rr_ExpenseExampleYear10

918

2002

rr_AnnualReturn2002

(13.09%)

2003

rr_AnnualReturn2003

39.33%

2004

rr_AnnualReturn2004

18.36%

2005

rr_AnnualReturn2005

10.36%

2006

rr_AnnualReturn2006

15.25%

2007

rr_AnnualReturn2007

7.43%

2008

rr_AnnualReturn2008

(27.33%)

2009

rr_AnnualReturn2009

30.37%

2010

rr_AnnualReturn2010

14.91%

2011

rr_AnnualReturn2011

(2.42%)

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

9.11%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2003

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

17.17%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(19.63%)

Perkins Mid Cap Value Fund | Class D Shares | Return Before Taxes | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(2.42%)

5 Years

rr_AverageAnnualReturnYear05

2.68%

10 Years

rr_AverageAnnualReturnYear10

7.60%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

11.78%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 12, 1998

Perkins Mid Cap Value Fund | Class D Shares | Return After Taxes on Distributions | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

(3.77%)

5 Years

rr_AverageAnnualReturnYear05

1.67%

10 Years

rr_AverageAnnualReturnYear10

6.50%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

10.32%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 12, 1998

Perkins Mid Cap Value Fund | Class D Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[1]

1 Year

rr_AverageAnnualReturnYear01

(0.08%)

5 Years

rr_AverageAnnualReturnYear05

2.08%

10 Years

rr_AverageAnnualReturnYear10

6.36%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

9.96%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 12, 1998

Perkins Mid Cap Value Fund | Class D Shares | Russell Midcap Value Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Russell Midcap® Value Index

1 Year

rr_AverageAnnualReturnYear01

(1.38%)

5 Years

rr_AverageAnnualReturnYear05

0.04%

10 Years

rr_AverageAnnualReturnYear10

7.67%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

7.70%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 12, 1998

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Janus Money Market Fund | Class D Shares

Fund summary

Janus Money Market Fund

INVESTMENT OBJECTIVES

Janus Money Market Fund seeks capital preservation and liquidity

with current income as a secondary objective.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses	Janus Money Market Fund Class D Shares Class D
Operating Expenses Column [Text]	Class D
Management Fees	0.20%
Other Expenses	0.47%
Total Annual Fund Operating Expenses	0.67%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Janus Money Market Fund Class D Shares Class D	Class D Shares	68	214	373	835

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objectives by investing primarily in high quality debt obligations and obligations of financial institutions. Debt obligations may include commercial paper, notes and bonds, and variable amount master demand notes. Obligations of financial institutions include certificates of deposit and time deposits. The Fund also intends to invest in repurchase agreements including those secured by U.S. Government agencies. Some government agencies backed by the full faith and credit of the United States are supported by the issuer’s ability to borrow from the United States Treasury, some are supported only by the credit of the issuer, and some are supported by the United States in some other way.

The Fund will:

• invest in high quality, short-term money market instruments that present minimal credit risks, as determined by Janus Capital

• invest only in U.S. dollar-denominated instruments that have a remaining maturity of 397 days or less (as calculated pursuant to Rule 2a-7 under the Investment Company Act of 1940, as amended)

• maintain a dollar-weighted average portfolio maturity of 60 days or less and maintain a dollar-weighted average portfolio life (portfolio maturity measured without reference to any maturity shortening provisions of adjustable rate securities by reference to their interest rate reset dates) of 120 days or less

PRINCIPAL INVESTMENT RISKS

Market Risk. The Fund’s yield will vary as the short-term securities in its portfolio mature and the proceeds are reinvested in securities with different interest rates. For capital preservation and liquidity, the Fund may have a greater concentration in short-term securities including, but not limited to, investing up to all of its assets in overnight securities, which may result in a reduction of the Fund’s yield. Over time, the real value of the Fund’s yield may be eroded by inflation. Although the Fund invests only in high-quality, short-term money market instruments, there is a risk that the value of the securities it holds will fall as a result of changes in interest rates, an issuer’s actual or perceived creditworthiness, or an issuer’s ability to meet its obligations. The credit quality of the Fund’s holdings can change rapidly in certain market environments and any downgrade or default of a portfolio security could cause the Fund’s share price or yield to fall.

Collateral Risk. With respect to collateral received in repurchase transactions or other investments, the Fund may have significant exposure to financial services, mortgage markets, and government agencies not secured by the full faith and credit of the United States. Such exposure, depending on market conditions, could have a negative impact on the Fund, including minimizing the value of any collateral.

Money Market Risk. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares, the predecessor share class. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses in effect during the periods shown, net of any applicable fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table shows how the Fund’s returns over different periods average out. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Annual Total Returns for Class D Shares (calendar year-end)

Best Quarter:  Fourth Quarter 2006  1.23%          Worst Quarter:  Third Quarter 2011  0.00%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 0.00%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns	Column	Label	1 Year	5 Years	10 Years	Since Inception	Inception Date
Janus Money Market Fund Class D Shares Class D Return Before Taxes	Class D Shares	Return Before Taxes	0.01%	1.39%	1.73%	3.08%	Feb. 14, 1995

The 7-day yield on December 31, 2011 was 0.01% for Janus Money Market Fund.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

INTECH International Fund | Class A, C, S, I, T Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

INTECH International Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

INTECH International Fund seeks long-term growth of capital.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

SHAREHOLDER FEES
(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

November 1, 2013

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 140% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

140.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 46 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

If Shares are redeemed:

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

If Shares are not redeemed:

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund invests primarily in common stocks from the universe of the Morgan Stanley Capital International (“MSCI”) EAFE^® (Europe, Australasia, Far East) Index, utilizing INTECH’s mathematical investment process. The MSCI EAFE^® Index is an MSCI index that is designed to measure the performance of the developed markets of Europe, Australasia, and the Far East. The Fund may also invest in foreign equity and debt securities.

The Fund pursues its investment objective by applying a mathematical investment process to construct an investment portfolio from the universe of common stocks within its named benchmark index. The goal of this process is to build a portfolio of stocks in a more efficient combination than the named benchmark index. The process seeks to capitalize on the natural volatility of the market by searching for stocks within the index that have high relative volatility (providing the potential for excess returns) but that essentially move in opposite directions or have low correlation to each other (providing the potential for lower relative risk). By constructing the portfolio in this manner and periodically rebalancing the portfolio to maintain potentially more efficient weightings, INTECH’s mathematical investment process seeks to create a portfolio that, over time, produces returns in excess of its named benchmark index with risks similar to that of the benchmark index. The rebalancing techniques used by INTECH may result in a higher portfolio turnover compared to a “buy and hold” fund strategy.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Foreign Exposure Risk. The Fund normally has significant exposure to foreign markets as a result of its investments in foreign securities, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Investment Process Risk. The proprietary mathematical investment process used by INTECH may not achieve the desired results. On an occasional basis, INTECH considers changes to its mathematical investment process. These changes may result in changes to the portfolio, might not provide the intended results, and may adversely impact the Fund’s performance.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

The biggest risk is that the Fund’s returns will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class I Shares, Class A Shares, Class C Shares, and Class S Shares of the Fund commenced operations on July 6, 2009, after the reorganization of each corresponding class of shares of Janus Adviser INTECH Risk-Managed International Fund (“JAD predecessor fund”) into each respective share class of the Fund. Class T Shares of the Fund commenced operations on July 6, 2009.

• The performance shown for Class I Shares, Class A Shares, Class C Shares, and Class S Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund’s Class I Shares, Class A Shares, Class C Shares, and Class S Shares prior to the reorganization, calculated using the fees and expenses of each respective share class of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class T Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund’s Class I Shares prior to the reorganization, calculated using the fees and expenses of Class T Shares, without the effect of any fee and expense limitations or waivers.

If Class T Shares of the Fund had been available during periods prior to July 6, 2009, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class I Shares, Class A Shares, Class C Shares, Class S Shares, and Class T Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-877-335-2687

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/advisor/mutual-funds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class I Shares (calendar year-end)

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Second Quarter 2009  22.50%        Worst Quarter:  Third Quarter 2008 −20.70%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 10.64%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

After-tax returns are calculated using distributions for the Fund’s Class I Shares for periods following July 6, 2009; and for the JAD predecessor fund’s Class I Shares for periods prior to July 6, 2009. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

INTECH International Fund | Class A, C, S, I, T Shares | Class A

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class A

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class A

Management Fees

rr_ManagementFeesOverAssets

0.55%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.62%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.42%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.16%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.26%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleYear01

711

3 Years

rr_ExpenseExampleYear03

998

5 Years

rr_ExpenseExampleYear05

1,307

10 Years

rr_ExpenseExampleYear10

2,179

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

711

3 Years

rr_ExpenseExampleNoRedemptionYear03

998

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,307

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,179

INTECH International Fund | Class A, C, S, I, T Shares | Class C

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class C

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

1.00%

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class C

Management Fees

rr_ManagementFeesOverAssets

0.55%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

0.70%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

2.25%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.24%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

2.01%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleYear01

328

3 Years

rr_ExpenseExampleYear03

703

5 Years

rr_ExpenseExampleYear05

1,205

10 Years

rr_ExpenseExampleYear10

2,585

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

228

3 Years

rr_ExpenseExampleNoRedemptionYear03

703

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,205

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,585

INTECH International Fund | Class A, C, S, I, T Shares | Class S

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class S

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class S

Management Fees

rr_ManagementFeesOverAssets

0.55%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.86%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.66%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.15%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.51%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleYear01

169

3 Years

rr_ExpenseExampleYear03

523

5 Years

rr_ExpenseExampleYear05

902

10 Years

rr_ExpenseExampleYear10

1,965

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

169

3 Years

rr_ExpenseExampleNoRedemptionYear03

523

5 Years

rr_ExpenseExampleNoRedemptionYear05

902

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,965

INTECH International Fund | Class A, C, S, I, T Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class I

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class I

Management Fees

rr_ManagementFeesOverAssets

0.55%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.58%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.13%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.12%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.01%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleYear01

115

3 Years

rr_ExpenseExampleYear03

359

5 Years

rr_ExpenseExampleYear05

622

10 Years

rr_ExpenseExampleYear10

1,375

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

115

3 Years

rr_ExpenseExampleNoRedemptionYear03

359

5 Years

rr_ExpenseExampleNoRedemptionYear05

622

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,375

2008

rr_AnnualReturn2008

(41.75%)

2009

rr_AnnualReturn2009

25.53%

2010

rr_AnnualReturn2010

9.76%

2011

rr_AnnualReturn2011

(13.48%)

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

10.64%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

22.50%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(20.70%)

INTECH International Fund | Class A, C, S, I, T Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class T

Management Fees

rr_ManagementFeesOverAssets

0.55%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.86%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.41%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.15%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.26%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleYear01

144

3 Years

rr_ExpenseExampleYear03

446

5 Years

rr_ExpenseExampleYear05

771

10 Years

rr_ExpenseExampleYear10

1,691

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

144

3 Years

rr_ExpenseExampleNoRedemptionYear03

446

5 Years

rr_ExpenseExampleNoRedemptionYear05

771

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,691

INTECH International Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class A

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class A Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[2]

1 Year

rr_AverageAnnualReturnYear01

(18.40%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

(7.88%)

Inception Date

rr_AverageAnnualReturnInceptionDate

May 02, 2007

INTECH International Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class C

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class C Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[3]

1 Year

rr_AverageAnnualReturnYear01

(14.54%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

(7.00%)

Inception Date

rr_AverageAnnualReturnInceptionDate

May 02, 2007

INTECH International Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class S

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class S Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(13.42%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

(6.78%)

Inception Date

rr_AverageAnnualReturnInceptionDate

May 02, 2007

INTECH International Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(13.48%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

(6.68%)

Inception Date

rr_AverageAnnualReturnInceptionDate

May 02, 2007

INTECH International Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(13.57%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

(8.16%)

Inception Date

rr_AverageAnnualReturnInceptionDate

May 02, 2007

INTECH International Fund | Class A, C, S, I, T Shares | Return After Taxes on Distributions | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

(13.63%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

(6.83%)

Inception Date

rr_AverageAnnualReturnInceptionDate

May 02, 2007

INTECH International Fund | Class A, C, S, I, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[4]

1 Year

rr_AverageAnnualReturnYear01

(8.62%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

(5.43%)

Inception Date

rr_AverageAnnualReturnInceptionDate

May 02, 2007

INTECH International Fund | Class A, C, S, I, T Shares | MSCI EAFE Index (net of foreign withholding taxes) (reflects no deduction for expenses, fees, or taxes, except foreign withholding taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

MSCI EAFE^® Index (net of foreign withholding taxes)

1 Year

rr_AverageAnnualReturnYear01

(12.14%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

(6.74%)

Inception Date

rr_AverageAnnualReturnInceptionDate

May 02, 2007

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, and Class S Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 1.00% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

[4] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Janus Government Money Market Fund | Class D Shares

Fund summary

Janus Government Money Market Fund

INVESTMENT OBJECTIVES

Janus Government Money Market Fund seeks capital preservation and liquidity

with current income as a secondary objective.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses

Janus Government Money Market Fund

Class D Shares

Class D

Operating Expenses Column [Text]

Class D

Management Fees

0.20%

Other Expenses

0.49%

Total Annual Fund Operating Expenses

0.69%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)

Expense Example, By Year, Column [Text]

1 Year

3 Years

5 Years

10 Years

Janus Government Money Market Fund Class D Shares Class D

Class D Shares

70

221

384

859

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objectives by investing exclusively in obligations issued and/or guaranteed as to principal and interest by the United States Government or by its agencies and instrumentalities, and repurchase agreements secured by such obligations. Although U.S. Government agencies and instrumentalities may be chartered or sponsored by Acts of Congress, their securities are not issued by, and may not be guaranteed by (i.e., backed by the full faith and credit of), the United States Treasury. Some government agency and instrumentality securities not backed by the full faith and credit of the United States are supported by the issuer’s ability to borrow from the U.S. Treasury, some are supported only by the credit of the issuer, and some are supported by the United States in some other way. For securities not backed by the full faith and credit of the U.S. Treasury, the Fund must look principally to the agency or instrumentality issuing or guaranteeing the securities for repayment and may not be able to assert a claim against the United States if the agency or instrumentality does not meet its commitment. The Fund’s investments in securities issued by U.S. Government agencies and instrumentalities may be significant.

The Fund will:

• invest in high quality, short-term money market instruments that present minimal credit risks, as determined by Janus Capital

• invest only in U.S. dollar-denominated instruments that have a remaining maturity of 397 days or less (as calculated pursuant to Rule 2a-7 under the Investment Company Act of 1940, as amended)

• maintain a dollar-weighted average portfolio maturity of 60 days or less and maintain a dollar-weighted average portfolio life (portfolio maturity measured without reference to any maturity shortening provisions of adjustable rate securities by reference to their interest rate reset dates) of 120 days or less

PRINCIPAL INVESTMENT RISKS

Market Risk. The Fund’s yield will vary as the short-term securities in its portfolio mature and the proceeds are reinvested in securities with different interest rates. For capital preservation and liquidity, the Fund may have a greater concentration in short-term securities including, but not limited to, investing up to all of its assets in overnight securities, which may result in a reduction of the Fund’s yield. Over time, the real value of the Fund’s yield may be eroded by inflation. Although the Fund invests only in high-quality, short-term money market instruments, there is a risk that the value of the securities it holds will fall as a result of changes in interest rates, an issuer’s actual or perceived creditworthiness, or an issuer’s ability to meet its obligations. The credit quality of the Fund’s holdings can change rapidly in certain market environments and any downgrade or default of a portfolio security could cause the Fund’s share price or yield to fall.

Collateral Risk. With respect to collateral received in repurchase transactions or other investments, the Fund may have significant exposure to government agencies not secured by the full faith and credit of the United States. Such exposure, depending on market conditions, could have a negative impact on the Fund, including minimizing the value of any collateral.

Money Market Risk. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares, the predecessor share class. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses in effect during the periods shown, net of any applicable fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table shows how the Fund’s returns over different periods average out. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Annual Total Returns for Class D Shares (calendar year-end)

Best Quarter:  Fourth Quarter 2006  1.21%          Worst Quarter:  Third Quarter 2011  0.00%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 0.00%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns

Column

Label

1 Year

5 Years

10 Years

Since Inception

Inception Date

Janus Government Money Market Fund Class D Shares Class D Return Before Taxes

Class D Shares

Return Before Taxes

none

1.29%

1.64%

2.99%

Feb. 14, 1995

The 7-day yield on December 31, 2011 was 0.00% for Janus Government Money Market Fund.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Janus Flexible Bond Fund | Class D Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Janus Flexible Bond Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Janus Flexible Bond Fund seeks to obtain maximum total return, consistent with preservation of capital.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 126% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

126.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund pursues its investment objective by primarily investing, under normal circumstances, at least 80% of its net assets in bonds. Bonds include, but are not limited to, government notes and bonds, corporate bonds, convertible bonds, mortgage-backed securities, and zero-coupon bonds. The Fund will invest at least 65% of its assets in investment grade debt securities. As of June 30, 2012, the Fund’s weighted average maturity was 7.9 years. The Fund will limit its investment in high-yield/high-risk bonds, also known as “junk bonds,” to 35% or less of its net assets. The Fund generates total return from a combination of current income and capital appreciation, but income is usually the dominant portion. The Fund may also invest in asset-backed securities, money market instruments, bank loans, and foreign debt securities (which may include investments in emerging markets). Due to the nature of the securities in which the Fund invests, it may have relatively high portfolio turnover compared to other Funds.

In addition, the Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. In particular, the Fund may use interest rate futures to manage portfolio risk. The Fund’s exposure to derivatives will vary. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

In addition to considering economic factors such as the effect of interest rates on the Fund’s investments, the portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income-producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Sovereign Debt Risk. The Fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However, investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

High-Yield/High-Risk Bond Risk. High-yield/high-risk bonds may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Bank Loan Risk. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. Participation interests and assignments involve credit, interest rate, and liquidity risk. In addition, the bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. To the extent the Fund invests in foreign debt securities, such investments are sensitive to changes in interest rates. Additionally, investments in securities of foreign governments involve the risk that a foreign government may not be willing or able to pay interest or repay principal when due. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares, the predecessor share class. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses in effect during the periods shown, net of any applicable fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-800-525-3713

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/allfunds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class D Shares (calendar year-end)

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Third Quarter 2009  5.58%          Worst Quarter:  Second Quarter 2004  −2.99%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 7.19%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; and for the Fund’s Class J Shares, the predecessor share class, for the periods prior to February 16, 2010. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Janus Flexible Bond Fund | Class D Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class D

Management Fees

rr_ManagementFeesOverAssets

0.41%

Other Expenses

rr_OtherExpensesOverAssets

0.18%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.59%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class D Shares

1 Year

rr_ExpenseExampleYear01

60

3 Years

rr_ExpenseExampleYear03

189

5 Years

rr_ExpenseExampleYear05

329

10 Years

rr_ExpenseExampleYear10

738

2002

rr_AnnualReturn2002

9.93%

2003

rr_AnnualReturn2003

6.37%

2004

rr_AnnualReturn2004

3.82%

2005

rr_AnnualReturn2005

1.79%

2006

rr_AnnualReturn2006

4.12%

2007

rr_AnnualReturn2007

6.87%

2008

rr_AnnualReturn2008

5.64%

2009

rr_AnnualReturn2009

12.54%

2010

rr_AnnualReturn2010

7.53%

2011

rr_AnnualReturn2011

6.63%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

7.19%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Sep. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

5.58%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Jun. 30, 2004

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(2.99%)

Janus Flexible Bond Fund | Class D Shares | Return Before Taxes | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

6.63%

5 Years

rr_AverageAnnualReturnYear05

7.82%

10 Years

rr_AverageAnnualReturnYear10

6.48%

Since Inception

rr_AverageAnnualReturnSinceInception

7.55%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 07, 1987

Janus Flexible Bond Fund | Class D Shares | Return After Taxes on Distributions | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

4.96%

5 Years

rr_AverageAnnualReturnYear05

5.94%

10 Years

rr_AverageAnnualReturnYear10

4.69%

Since Inception

rr_AverageAnnualReturnSinceInception

4.93%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 07, 1987

Janus Flexible Bond Fund | Class D Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

1 Year

rr_AverageAnnualReturnYear01

4.52%

5 Years

rr_AverageAnnualReturnYear05

5.63%

10 Years

rr_AverageAnnualReturnYear10

4.51%

Since Inception

rr_AverageAnnualReturnSinceInception

4.88%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 07, 1987

Janus Flexible Bond Fund | Class D Shares | Barclays U.S. Aggregate Bond Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Barclays U.S. Aggregate Bond Index

1 Year

rr_AverageAnnualReturnYear01

7.84%

5 Years

rr_AverageAnnualReturnYear05

6.50%

10 Years

rr_AverageAnnualReturnYear10

5.78%

Since Inception

rr_AverageAnnualReturnSinceInception

7.34%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 07, 1987

XML

Janus Short-Term Bond Fund | Class A, C, S, I, N, T Shares

Fund summary

Janus Short-Term Bond Fund

INVESTMENT OBJECTIVE

Janus Short-Term Bond Fund seeks as high a level of current income as is consistent with preservation of capital.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 51 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.

SHAREHOLDER FEES
(fees paid directly from your investment)

Shareholder Fees Janus Short-Term Bond Fund Class A, C, S, I, N, T Shares	Class A	Class C	Class S	Class I	Class N	Class T
Shareholder Fees Column [Text]	Class A	Class C	Class S	Class I	Class N	Class T
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	2.50%	none	none	none	none	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	none	1.00%	none	none	none	none

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Janus Short-Term Bond Fund Class A, C, S, I, N, T Shares		Class A		Class C	Class S	Class I	Class N		Class T
Operating Expenses Column [Text]		Class A		Class C	Class S	Class I	Class N		Class T
Management Fees		0.55%		0.55%	0.55%	0.55%	0.55%		0.55%
Distribution/Service (12b-1) Fees		0.25%		1.00%	0.25%	none	none		none
Other Expenses		0.14%	[1]	0.13%	0.29%	0.09%	0.05%	[1]	0.29%
Total Annual Fund Operating Expenses	[2]	0.94%		1.68%	1.09%	0.64%	0.60%		0.84%
Fee Waiver	[2]	0.14%		0.13%	0.04%	0.09%	0.05%		0.04%
Total Annual Fund Operating Expenses After Fee Waiver	[2]	0.80%		1.55%	1.05%	0.55%	0.55%		0.80%

EXAMPLE:

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

If Shares are redeemed:

Expense Example Janus Short-Term Bond Fund Class A, C, S, I, N, T Shares (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	344	542	757	1,376
Class C	Class C Shares	271	530	913	1,987
Class S	Class S Shares	111	347	601	1,329
Class I	Class I Shares	65	205	357	798
Class N	Class N Shares	61	192	335	750
Class T	Class T Shares	86	268	466	1,037

If Shares are not redeemed:

Expense Example, No Redemption Janus Short-Term Bond Fund Class A, C, S, I, N, T Shares (USD $)	Expense Example, No Redemption, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	344	542	757	1,376
Class C	Class C Shares	171	530	913	1,987
Class S	Class S Shares	111	347	601	1,329
Class I	Class I Shares	65	205	357	798
Class N	Class N Shares	61	192	335	750
Class T	Class T Shares	86	268	466	1,037

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 93% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund invests, under normal circumstances, at least 80% of its net assets in short- and intermediate-term securities such as corporate bonds or notes or government securities, including agency securities. The Fund may invest up to 35% of its net assets in high-yield/high risk bonds, also known as “junk bonds.” The Fund expects to maintain an average-weighted effective maturity of three years or less under normal circumstances. As of June 30, 2012, the Fund’s weighted average maturity was 2.4 years. The Fund may also invest in bank loans, mortgage-backed securities, asset-backed securities, and foreign debt securities (which may include investments in emerging markets). Due to the nature of securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

“Effective” maturity differs from actual maturity, which may be longer. In calculating the “effective” maturity the portfolio managers will estimate the effect of expected principal payments and call provisions on securities held in the portfolio. This gives the portfolio managers some additional flexibility in the securities they purchase, but all else being equal, could result in more volatility than if the Fund calculated an actual maturity target.

In addition, the Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. In particular, the Fund may use interest rate futures to manage portfolio risk. The Fund’s exposure to derivatives will vary. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

In addition to considering economic factors such as the effect of interest rates on the Fund’s investments, the portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income-producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

PRINCIPAL INVESTMENT RISKS

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

Sovereign Debt Risk. The Fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However, investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Bank Loan Risk. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. Participation interests and assignments involve credit, interest rate, and liquidity risk. In addition, the bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. To the extent the Fund invests in foreign debt securities, such investments are sensitive to changes in interest rates. Additionally, investments in securities of foreign governments involve the risk that a foreign government may not be willing or able to pay interest or repay principal when due. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

High-Yield/High-Risk Bond Risk. High-yield/high-risk bonds may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares, the initial share class) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund commenced operations on July 6, 2009. Class N Shares of the Fund commenced operations on May 31, 2012.

• The performance shown for Class T Shares is calculated using the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class A Shares, Class C Shares, Class S Shares, and Class I Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers.
• The performance shown for Class N Shares for periods prior to December 31, 2011, reflects the performance of the Fund’s Class T Shares, calculated using the fees and expenses of Class T Shares, net of any applicable fee and expense limitations or waivers.

If Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund had been available during periods prior to July 6, 2009, or Class N Shares of the Fund had been available during periods prior to December 31, 2011, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class N Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Annual Total Returns for Class T Shares (calendar year-end)

Best Quarter:  Second Quarter 2009  3.18%          Worst Quarter:  Second Quarter 2008  −0.90%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 2.96%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Janus Short-Term Bond Fund Class A, C, S, I, N, T Shares	Column	Label		1 Year	5 Years	10 Years	Since Inception	Inception Date
Class T Shares Return Before Taxes	Class T Shares	Return Before Taxes		1.37%	4.60%	3.81%	4.64%	Sep. 01, 1992
Class T Shares Return After Taxes on Distributions	Class T Shares	Return After Taxes on Distributions		0.58%	3.40%	2.62%	2.92%	Sep. 01, 1992
Class T Shares Return After Taxes on Distributions and Sale of Fund Shares	Class T Shares	Return After Taxes on Distributions and Sale of Fund Shares	[1]	0.93%	3.24%	2.56%	2.90%	Sep. 01, 1992
Class A Shares Return Before Taxes	Class A Shares	Return Before Taxes	[2]	(1.20%)	3.41%	2.98%	3.98%	Sep. 01, 1992
Class C Shares Return Before Taxes	Class C Shares	Return Before Taxes	[3]	(0.03%)	3.84%	2.87%	3.58%	Sep. 01, 1992
Class S Shares Return Before Taxes	Class S Shares	Return Before Taxes		1.13%	4.09%	3.25%	4.05%	Sep. 01, 1992
Class I Shares Return Before Taxes	Class I Shares	Return Before Taxes		1.62%	4.59%	3.69%	4.47%	Sep. 01, 1992
Class N Shares Return Before Taxes	Class N Shares	Return Before Taxes		1.37%	4.60%	3.81%	4.64%	Sep. 01, 1992
Barclays 1-3 Year U.S. Government/Credit Index (reflects no deduction for expenses, fees, or taxes)		Barclays 1-3 Year U.S. Government/Credit Index		1.59%	3.99%	3.63%	4.80%	Sep. 01, 1992

After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares, the initial share class). After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

[1] Other Expenses for Class A Shares and Class N Shares are based on the estimated expenses that the Shares expect to incur.

[2] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, and Class S Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 0.55% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

XML

INTECH International Fund | Class A, C, S, I, T Shares

Fund summary

INTECH International Fund

INVESTMENT OBJECTIVE

INTECH International Fund seeks long-term growth of capital.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 46 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.

SHAREHOLDER FEES
(fees paid directly from your investment)

Shareholder Fees INTECH International Fund Class A, C, S, I, T Shares	Class A	Class C	Class S	Class I	Class T
Shareholder Fees Column [Text]	Class A	Class C	Class S	Class I	Class T
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	5.75%	none	none	none	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	none	1.00%	none	none	none

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses INTECH International Fund Class A, C, S, I, T Shares		Class A	Class C	Class S	Class I	Class T
Operating Expenses Column [Text]		Class A	Class C	Class S	Class I	Class T
Management Fees		0.55%	0.55%	0.55%	0.55%	0.55%
Distribution/Service (12b-1) Fees		0.25%	1.00%	0.25%	none	none
Other Expenses		0.62%	0.70%	0.86%	0.58%	0.86%
Total Annual Fund Operating Expenses	[1]	1.42%	2.25%	1.66%	1.13%	1.41%
Fee Waiver	[1]	0.16%	0.24%	0.15%	0.12%	0.15%
Total Annual Fund Operating Expenses After Fee Waiver	[1]	1.26%	2.01%	1.51%	1.01%	1.26%

EXAMPLE:

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

If Shares are redeemed:

Expense Example INTECH International Fund Class A, C, S, I, T Shares (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	711	998	1,307	2,179
Class C	Class C Shares	328	703	1,205	2,585
Class S	Class S Shares	169	523	902	1,965
Class I	Class I Shares	115	359	622	1,375
Class T	Class T Shares	144	446	771	1,691

If Shares are not redeemed:

Expense Example, No Redemption INTECH International Fund Class A, C, S, I, T Shares (USD $)	Expense Example, No Redemption, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	711	998	1,307	2,179
Class C	Class C Shares	228	703	1,205	2,585
Class S	Class S Shares	169	523	902	1,965
Class I	Class I Shares	115	359	622	1,375
Class T	Class T Shares	144	446	771	1,691

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 140% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund invests primarily in common stocks from the universe of the Morgan Stanley Capital International (“MSCI”) EAFE^® (Europe, Australasia, Far East) Index, utilizing INTECH’s mathematical investment process. The MSCI EAFE^® Index is an MSCI index that is designed to measure the performance of the developed markets of Europe, Australasia, and the Far East. The Fund may also invest in foreign equity and debt securities.

The Fund pursues its investment objective by applying a mathematical investment process to construct an investment portfolio from the universe of common stocks within its named benchmark index. The goal of this process is to build a portfolio of stocks in a more efficient combination than the named benchmark index. The process seeks to capitalize on the natural volatility of the market by searching for stocks within the index that have high relative volatility (providing the potential for excess returns) but that essentially move in opposite directions or have low correlation to each other (providing the potential for lower relative risk). By constructing the portfolio in this manner and periodically rebalancing the portfolio to maintain potentially more efficient weightings, INTECH’s mathematical investment process seeks to create a portfolio that, over time, produces returns in excess of its named benchmark index with risks similar to that of the benchmark index. The rebalancing techniques used by INTECH may result in a higher portfolio turnover compared to a “buy and hold” fund strategy.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Foreign Exposure Risk. The Fund normally has significant exposure to foreign markets as a result of its investments in foreign securities, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Investment Process Risk. The proprietary mathematical investment process used by INTECH may not achieve the desired results. On an occasional basis, INTECH considers changes to its mathematical investment process. These changes may result in changes to the portfolio, might not provide the intended results, and may adversely impact the Fund’s performance.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class I Shares, Class A Shares, Class C Shares, and Class S Shares of the Fund commenced operations on July 6, 2009, after the reorganization of each corresponding class of shares of Janus Adviser INTECH Risk-Managed International Fund (“JAD predecessor fund”) into each respective share class of the Fund. Class T Shares of the Fund commenced operations on July 6, 2009.

• The performance shown for Class I Shares, Class A Shares, Class C Shares, and Class S Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund’s Class I Shares, Class A Shares, Class C Shares, and Class S Shares prior to the reorganization, calculated using the fees and expenses of each respective share class of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class T Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund’s Class I Shares prior to the reorganization, calculated using the fees and expenses of Class T Shares, without the effect of any fee and expense limitations or waivers.

If Class T Shares of the Fund had been available during periods prior to July 6, 2009, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class I Shares, Class A Shares, Class C Shares, Class S Shares, and Class T Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Annual Total Returns for Class I Shares (calendar year-end)

Best Quarter:  Second Quarter 2009  22.50%        Worst Quarter:  Third Quarter 2008 −20.70%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 10.64%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns INTECH International Fund Class A, C, S, I, T Shares	Column	Label		1 Year	Since Inception of Predecessor Fund	Inception Date
Class I Shares Return Before Taxes	Class I Shares	Return Before Taxes		(13.48%)	(6.68%)	May 02, 2007
Class I Shares Return After Taxes on Distributions	Class I Shares	Return After Taxes on Distributions		(13.63%)	(6.83%)	May 02, 2007
Class I Shares Return After Taxes on Distributions and Sale of Fund Shares	Class I Shares	Return After Taxes on Distributions and Sale of Fund Shares	[1]	(8.62%)	(5.43%)	May 02, 2007
Class A Shares Return Before Taxes	Class A Shares	Return Before Taxes	[2]	(18.40%)	(7.88%)	May 02, 2007
Class C Shares Return Before Taxes	Class C Shares	Return Before Taxes	[3]	(14.54%)	(7.00%)	May 02, 2007
Class S Shares Return Before Taxes	Class S Shares	Return Before Taxes		(13.42%)	(6.78%)	May 02, 2007
Class T Shares Return Before Taxes	Class T Shares	Return Before Taxes		(13.57%)	(8.16%)	May 02, 2007
MSCI EAFE Index (net of foreign withholding taxes) (reflects no deduction for expenses, fees, or taxes, except foreign withholding taxes)		MSCI EAFE® Index (net of foreign withholding taxes)		(12.14%)	(6.74%)	May 02, 2007

After-tax returns are calculated using distributions for the Fund’s Class I Shares for periods following July 6, 2009; and for the JAD predecessor fund’s Class I Shares for periods prior to July 6, 2009. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, and Class S Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 1.00% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

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Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares

Fund summary

Perkins Mid Cap Value Fund

INVESTMENT OBJECTIVE

Perkins Mid Cap Value Fund seeks capital appreciation.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 60 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.

SHAREHOLDER FEES
(fees paid directly from your investment)

Shareholder Fees Perkins Mid Cap Value Fund Class A, C, S, I, N, R, T Shares	Class A	Class C	Class S	Class I	Class N	Class R	Class T
Shareholder Fees Column [Text]	Class A	Class C	Class S	Class I	Class N	Class R	Class T
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	5.75%	none	none	none	none	none	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	none	1.00%	none	none	none	none	none

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Perkins Mid Cap Value Fund Class A, C, S, I, N, R, T Shares		Class A	Class C	Class S	Class I	Class N		Class R	Class T
Operating Expenses Column [Text]		Class A	Class C	Class S	Class I	Class N		Class R	Class T
Management Fees (may adjust up or down)		0.54%	0.54%	0.54%	0.54%	0.54%		0.54%	0.54%
Distribution/Service (12b-1) Fees		0.25%	1.00%	0.25%	none	none		0.50%	none
Other Expenses		0.26%	0.24%	0.30%	0.19%	0.04%	[1]	0.30%	0.30%
Total Annual Fund Operating Expenses	[2]	1.05%	1.78%	1.09%	0.73%	0.58%		1.34%	0.84%
Fee Waiver	[2]	0.04%	0.02%	none	none	none		none	none
Total Annual Fund Operating Expenses After Fee Waiver	[2]	1.01%	1.76%	1.09%	0.73%	0.58%		1.34%	0.84%

EXAMPLE:

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

If Shares are redeemed:

Expense Example Perkins Mid Cap Value Fund Class A, C, S, I, N, R, T Shares (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	676	890	1,121	1,784
Class C	Class C Shares	281	560	964	2,095
Class S	Class S Shares	111	347	601	1,329
Class I	Class I Shares	75	233	406	906
Class N	Class N Shares	59	186	324	726
Class R	Class R Shares	136	425	734	1,613
Class T	Class T Shares	86	268	466	1,037

If Shares are not redeemed:

Expense Example, No Redemption Perkins Mid Cap Value Fund Class A, C, S, I, N, R, T Shares (USD $)	Expense Example, No Redemption, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	676	890	1,121	1,784
Class C	Class C Shares	181	560	964	2,095
Class S	Class S Shares	111	347	601	1,329
Class I	Class I Shares	75	233	406	906
Class N	Class N Shares	59	186	324	726
Class R	Class R Shares	136	425	734	1,613
Class T	Class T Shares	86	268	466	1,037

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 54% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objective by investing primarily in common stocks selected for their capital appreciation potential. The Fund primarily invests in the common stocks of mid-sized companies whose stock prices the portfolio managers believe to be undervalued. The Fund invests, under normal circumstances, at least 80% of its net assets in equity securities of companies whose market capitalization falls, at the time of purchase, within the 12-month average of the capitalization range of the Russell Midcap^® Value Index. This average is updated monthly. The market capitalizations within the index will vary, but as of June 30, 2012, they ranged from approximately $1.3 billion to $18.5 billion. The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets. The Fund may invest, under normal circumstances, up to 20% of its net assets in securities of companies having market capitalizations outside of the aforementioned market capitalization ranges. In addition, when the portfolio managers believe that market conditions are unfavorable for investing, or when they are otherwise unable to locate attractive investment opportunities, the Fund may invest up to 20% of its net assets in cash or similar investments.

The Fund focuses on companies that have fallen out of favor with the market or that appear to be temporarily misunderstood by the investment community. The Fund’s portfolio managers generally look for companies with:

•   strong balance sheets and solid recurring free cash flows
•   attractive relative and absolute valuation ratios or that have underperformed recently
•   favorable reward to risk characteristics

The Fund may also invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. The Fund has and is expected to continue to buy and sell put and call options, particularly on market indices, for hedging purposes (to offset risks associated with an investment, currency exposure, or market conditions) and to enhance returns. The Fund’s exposure to derivatives will vary, is not limited to those derivatives listed, and could be significant at times. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s portfolio managers. When the Fund’s investments in cash or similar investments increase due to a lack of favorable investment opportunities or other extraordinary factors, the Fund may not participate in market advances or declines to the same extent that it would if the Fund had been fully invested.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Mid-Sized Companies Risk. The Fund’s investments in securities issued by mid-sized companies may involve greater risks than are customarily associated with larger, more established companies. Securities issued by mid-sized companies tend to be more volatile than securities issued by larger or more established companies and may underperform as compared to the securities of larger companies.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class R Shares of the Fund commenced operations on July 6, 2009. Class N Shares of the Fund commenced operations on May 31, 2012.

•  The performance shown for Class T Shares for periods following April 21, 2003, reflects the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class T Shares reflects the historical performance of Berger Mid Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Mid Cap Value Fund – Investor Shares into the Fund’s former Class J Shares).
•  The performance shown for Class A Shares, Class C Shares, Class S Shares, and Class R Shares reflects the performance of the Fund’s Class J Shares (formerly named Investor Shares) from April 21, 2003 to July 6, 2009, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers. For periods prior to April 21, 2003, the performance shown for Class A Shares, Class C Shares, Class S Shares, and Class R Shares reflects the historical performance of Berger Mid Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Mid Cap Value Fund – Investor Shares into the Fund’s former Class J Shares), calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers.
•  The performance shown for Class I Shares reflects the performance of the Fund’s Class J Shares (formerly named Investor Shares) from April 21, 2003 to July 6, 2009, calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class I Shares reflects the historical performance of Berger Mid Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Mid Cap Value Fund – Investor Shares into the Fund’s former Class J Shares), calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers.
•  The performance shown for Class N Shares reflects the performance of the Fund’s Class T Shares from July 6, 2009 to December 31, 2011, calculated using the fees and expenses of Class T Shares, net of any applicable fee and expense limitations or waivers. For the period from April 21, 2003 to July 6, 2009, the performance shown for Class N Shares reflects the performance of the Fund’s Class J Shares (formerly named Investor Shares), calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class N Shares reflects the historical performance of Berger Mid Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Mid Cap Value Fund – Investor Shares into the Fund’s former Class J Shares), calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers.

If Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class R Shares of the Fund had been available during periods prior to July 6, 2009, or Class N Shares of the Fund had been available during periods prior to December 31, 2011, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, Class I Shares, Class N Shares, and Class R Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Annual Total Returns for Class T Shares (calendar year-end)

Best Quarter: Second Quarter 2003 17.17%           Worst Quarter: Fourth Quarter 2008 −19.63%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 9.06%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Perkins Mid Cap Value Fund Class A, C, S, I, N, R, T Shares	Column	Label		1 Year	5 Years	10 Years	Since Inception of Predecessor Fund	Inception Date
Class T Shares Return Before Taxes	Class T Shares	Return Before Taxes		(2.55%)	2.63%	7.58%	11.76%	Aug. 12, 1998
Class T Shares Return After Taxes on Distributions	Class T Shares	Return After Taxes on Distributions		(3.88%)	1.63%	6.48%	10.31%	Aug. 12, 1998
Class T Shares Return After Taxes on Distributions and Sale of Fund Shares	Class T Shares	Return After Taxes on Distributions and Sale of Fund Shares	[1]	(0.18%)	2.04%	6.34%	9.94%	Aug. 12, 1998
Class A Shares Return Before Taxes	Class A Shares	Return Before Taxes	[2]	(8.32%)	1.24%	6.75%	11.12%	Aug. 12, 1998
Class C Shares Return Before Taxes	Class C Shares	Return Before Taxes	[3]	(4.27%)	1.71%	6.62%	10.90%	Aug. 12, 1998
Class S Shares Return Before Taxes	Class S Shares	Return Before Taxes		(2.73%)	2.34%	7.27%	11.51%	Aug. 12, 1998
Class I Shares Return Before Taxes	Class I Shares	Return Before Taxes		(2.43%)	2.63%	7.58%	11.76%	Aug. 12, 1998
Class N Shares Return Before Taxes	Class N Shares	Return Before Taxes		(2.55%)	2.63%	7.58%	11.76%	Aug. 12, 1998
Class R Shares Return Before Taxes	Class R Shares	Return Before Taxes		(3.01%)	2.08%	7.00%	11.29%	Aug. 12, 1998
Russell Midcap Value Index (reflects no deduction for expenses, fees, or taxes)		Russell Midcap® Value Index		(1.38%)	0.04%	7.67%	7.70%	Aug. 12, 1998

After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares) for the periods following April 21, 2003; and for Berger Mid Cap Value Fund – Investor Shares for periods prior to April 21, 2003. If Class T Shares of the Fund had been available during the periods prior to April 21, 2003, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

[1] Other Expenses for Class N Shares are based on the estimated expenses that the Shares expect to incur during their initial fiscal period.

[2] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding any performance adjustments to management fees, the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, Class S Shares, and Class R Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 0.86% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

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Perkins Large Cap Value Fund | Class D Shares

Fund summary

Perkins Large Cap Value Fund

INVESTMENT OBJECTIVE

Perkins Large Cap Value Fund seeks capital appreciation.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses	Perkins Large Cap Value Fund Class D Shares Class D
Operating Expenses Column [Text]	Class D
Management Fees (may adjust up or down)	0.62%
Other Expenses	0.33%
Total Annual Fund Operating Expenses	0.95%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Perkins Large Cap Value Fund Class D Shares Class D	Class D Shares	97	303	525	1,166

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 52% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objective by investing primarily in common stocks selected for their capital appreciation potential. The Fund primarily invests in the common stocks of large-sized companies whose stock prices the portfolio managers believe to be undervalued. The Fund invests, under normal circumstances, at least 80% of its net assets in equity securities of companies having, at the time of purchase, market capitalizations equal to or greater than the median market capitalization of companies included in the Russell 1000^® Value Index. The market capitalizations within the index will vary, but as of June 30, 2012, they ranged from approximately $1.3 billion to $400.1 billion, and the median market capitalization was $4.7 billion. The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets. The Fund may invest, under normal circumstances, up to 20% of its net assets in securities of companies having market capitalizations outside of the aforementioned market capitalization ranges. In addition, when the portfolio managers believe that market conditions are unfavorable for investing, or when they are otherwise unable to locate attractive investment opportunities, the Fund may invest up to 20% of its net assets in exchange-traded funds (“ETFs”), including commodity-related ETFs, cash or similar investments.

The Fund focuses on companies that have fallen out of favor with the market or that appear to be temporarily misunderstood by the investment community. The Fund’s portfolio managers generally look for companies with:

• strong balance sheets and solid recurring free cash flows
• attractive relative and absolute valuation ratios or that have underperformed recently
• favorable reward to risk characteristics

The Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices, as substitutes for securities in which the Fund invests. The Fund may invest in derivative instruments (by taking long and/or short positions) for different purposes, including hedging (to offset risks associated with an investment, currency exposure, or market conditions) and to earn income and enhance returns. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s portfolio managers. When the Fund’s investments in cash or similar investments increase due to a lack of favorable investment opportunities or other extraordinary factors, the Fund may not participate in market advances or declines to the same extent that it would if the Fund had been fully invested.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio.

Exchange-Traded Funds Risk. The Fund may invest in ETFs which are typically open-end investment companies that are traded on a national securities exchange. ETFs typically incur fees, such as investment advisory fees and other operating expenses that are separate from those of the Fund, which will be indirectly paid by the Fund. As a result, the cost of investing in the Fund may be higher than the cost of investing directly in ETFs and may be higher than other mutual funds that invest directly in stocks and bonds. Further, the price movement of an ETF may fluctuate against the underlying securities or commodities it tracks and may result in a loss. Because the value of ETF shares depends on the demand in the market, the Fund may not be able to purchase or sell an ETF at the most optimal time, which could adversely affect the Fund’s performance.

The ETFs in which the Fund invests are subject to specific risks, depending on the investment strategy of the ETF. In turn, the Fund will be subject to substantially the same risks as those associated with direct exposure to the securities or commodities held by the ETF. Because the Fund may invest in a broad range of ETFs, such risks may include, but are not limited to, leverage risk, foreign exposure risk, and commodities risk.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010. The performance shown for Class D Shares for the period July 6, 2009 to February 16, 2010, reflects the performance of the Fund’s Class I Shares, calculated using the fees and expenses of Class D Shares, without the effect of any fee and expense limitations or waivers. Performance shown for the period prior to July 6, 2009, reflects the historical performance of the Janus Adviser Perkins Large Cap Value Fund’s (“JAD predecessor fund”) Class I Shares prior to the reorganization of Class I Shares of the JAD predecessor fund into Class I Shares of the Fund, calculated using the fees and expenses of Class D Shares, without the effect of any fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Annual Total Returns for Class D Shares (calendar year-end)

Best Quarter:  Second Quarter 2009  15.02%          Worst Quarter:  Third Quarter 2011  −14.77%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 13.38%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Perkins Large Cap Value Fund Class D Shares	Column	Label		1 Year	Since Inception of Predecessor Fund	Inception Date
Class D Return Before Taxes	Class D Shares	Return Before Taxes		(0.37%)	11.29%	Dec. 31, 2008
Class D Return After Taxes on Distributions	Class D Shares	Return After Taxes on Distributions		(1.63%)	10.50%	Dec. 31, 2008
Class D Return After Taxes on Distributions and Sale of Fund Shares	Class D Shares	Return After Taxes on Distributions and Sale of Fund Shares	[1]	0.69%	9.52%	Dec. 31, 2008
Russell 1000 Value Index (reflects no deduction for expenses, fees, or taxes)		Russell 1000® Value Index		0.39%	11.55%	Dec. 31, 2008

After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; for the Fund’s Class I Shares for the period following July 6, 2009; and for the JAD predecessor fund’s Class I Shares for the period prior to July 6, 2009. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

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Perkins Small Cap Value Fund | Class A, C, S, I, N, R, T Shares

Fund summary

Perkins Small Cap Value Fund

INVESTMENT OBJECTIVE

Perkins Small Cap Value Fund seeks capital appreciation.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the "Purchases" section on page 60 of the Fund's Prospectus and in the "Purchases" section on page 83 of the Fund's Statement of Additional Information.

SHAREHOLDER FEES
(fees paid directly from your investment)

Shareholder Fees Perkins Small Cap Value Fund Class A, C, S, I, N, R, T Shares	Class A	Class C	Class S	Class I	Class N	Class R	Class T
Shareholder Fees Column [Text]	Class A	Class C	Class S	Class I	Class N	Class R	Class T
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	5.75%	none	none	none	none	none	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	none	1.00%	none	none	none	none	none

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Perkins Small Cap Value Fund Class A, C, S, I, N, R, T Shares		Class A	Class C	Class S	Class I	Class N	Class R	Class T
Operating Expenses Column [Text]		Class A	Class C	Class S	Class I	Class N	Class R	Class T
Management Fees (may adjust up or down)		0.75%	0.75%	0.75%	0.75%	0.75%	0.75%	0.75%
Distribution/Service (12b-1) Fees		0.25%	1.00%	0.25%	none	none	0.50%	none
Other Expenses	[1]	0.39%	0.30%	0.29%	0.14%	0.04%	0.29%	0.30%
Total Annual Fund Operating Expenses	[2]	1.39%	2.05%	1.29%	0.89%	0.79%	1.54%	1.05%
Fee Waiver	[2]	0.15%	0.06%	none	none	none	none	none
Total Annual Fund Operating Expenses After Fee Waiver	[2]	1.24%	1.99%	1.29%	0.89%	0.79%	1.54%	1.05%

EXAMPLE:

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

If Shares are redeemed:

Expense Example Class A, C, S, I, N, R, T Shares Perkins Small Cap Value Fund (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	708	990	1,292	2,148
Class C	Class C Shares	308	643	1,103	2,379
Class S	Class S Shares	131	409	708	1,556
Class I	Class I Shares	91	284	493	1,096
Class N	Class N Shares	81	252	439	978
Class R	Class R Shares	157	486	839	1,834
Class T	Class T Shares	107	334	579	1,283

If Shares are not redeemed:

Expense Example, No Redemption Class A, C, S, I, N, R, T Shares Perkins Small Cap Value Fund (USD $)	Expense Example, No Redemption, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	708	990	1,292	2,148
Class C	Class C Shares	208	643	1,103	2,379
Class S	Class S Shares	131	409	708	1,556
Class I	Class I Shares	91	284	493	1,096
Class N	Class N Shares	81	252	439	978
Class R	Class R Shares	157	486	839	1,834
Class T	Class T Shares	107	334	579	1,283

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 62% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objective by investing primarily in the common stocks of small companies whose stock prices are believed to be undervalued by the Fund’s portfolio managers. The Fund invests, under normal circumstances, at least 80% of its net assets in equity securities of small companies whose market capitalization, at the time of initial purchase, is less than the 12-month average of the maximum market capitalization for companies included in the Russell 2000^® Value Index. This average is updated monthly. The market capitalizations within the index will vary, but as of June 30, 2012, they ranged from approximately $85 million to $2.7 billion. The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets. The Fund may invest, under normal circumstances, up to 20% of its net assets in securities of companies having market capitalizations outside of the aforementioned market capitalization ranges. In addition, when the portfolio managers believe that market conditions are unfavorable for investing, or when they are otherwise unable to locate attractive investment opportunities, the Fund may invest up to 20% of its net assets in cash or similar investments.

The Fund’s securities selection focuses on companies that are out of favor with markets or have not yet been discovered by the broader investment community.

The Fund’s portfolio managers generally look for companies with:

• strong balance sheets and solid recurring free cash flows
• attractive relative and absolute valuation ratios or that have underperformed recently
• favorable reward to risk characteristics

The portfolio managers’ philosophy is to weigh a security’s downside risk before considering its upside potential, which may help provide an element of capital preservation.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s portfolio managers. When the Fund’s investments in cash or similar investments increase due to a lack of favorable investment opportunities or other extraordinary factors, the Fund may not participate in market advances or declines to the same extent that it would if the Fund had been fully invested.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Small-Sized Companies Risk. The Fund’s investments in securities issued by small-sized companies, which tend to be smaller, start-up companies offering emerging products or services, may involve greater risks than are customarily associated with larger, more established companies. Securities issued by small-sized companies tend to be more volatile and somewhat more speculative than securities issued by larger or more established companies and may underperform as compared to the securities of larger companies.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class R Shares of the Fund commenced operations on July 6, 2009. Class N Shares of the Fund commenced operations on May 31, 2012.

• The performance shown for Class T Shares for periods following April 21, 2003, reflects the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class T Shares reflects the historical performance of Berger Small Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Investor Shares into the Fund’s former Class J Shares).
• The performance shown for Class A Shares, Class C Shares, Class S Shares, and Class R Shares reflects the performance of the Fund’s Class J Shares (formerly named Investor Shares) from April 21, 2003 to July 6, 2009, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers. For periods prior to April 21, 2003, the performance shown for Class A Shares, Class C Shares, Class S Shares, and Class R Shares reflects the historical performance of Berger Small Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Investor Shares into the Fund’s former Class J Shares), calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers.
• The performance shown for Class I Shares reflects the performance of the Fund’s Class J Shares (formerly named Investor Shares) from April 21, 2003 to July 6, 2009, calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class I Shares reflects the historical performance of Berger Small Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Investor Shares into the Fund’s former Class J Shares), calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class N Shares reflects the performance of the Fund’s Class T Shares from July 6, 2009 to December 31, 2011, calculated using the fees and expenses of Class T Shares, net of any applicable fee and expense limitations or waivers. For the period from April 21, 2003 to July 6, 2009, the performance shown for Class N Shares reflects the performance of the Fund’s Class J Shares (formerly named Investor Shares), calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class N Shares reflects the historical performance of Berger Small Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Investor Shares into the Fund’s former Class J Shares), calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers.

If Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class R Shares of the Fund had been available during periods prior to July 6, 2009, or Class N Shares of the Fund had been available during periods prior to December 31, 2011, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, Class I Shares, Class N Shares, and Class R Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Annual Total Returns for Class T Shares (calendar year-end)

Best Quarter:  Second Quarter 2009  23.04%          Worst Quarter:  Third Quarter 2002  −22.57%

The Fund's year-to-date return as of the calendar quarter ended September 30, 2012 was 6.24%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Perkins Small Cap Value Fund Class A, C, S, I, N, R, T Shares	Column	Label		1 Year	5 Years	10 Years
Class T Shares Return Before Taxes	Class T Shares	Return Before Taxes		(3.43%)	4.60%	7.23%
Class T Shares Return After Taxes on Distributions	Class T Shares	Return After Taxes on Distributions		(5.87%)	2.87%	5.36%
Class T Shares Return After Taxes on Distributions and Sale of Fund Shares	Class T Shares	Return After Taxes on Distributions and Sale of Fund Shares	[1]	(0.57%)	3.41%	5.73%
Class A Shares Return Before Taxes	Class A Shares	Return Before Taxes	[2]	(9.12%)	3.17%	6.34%
Class C Shares Return Before Taxes	Class C Shares	Return Before Taxes	[3]	(5.21%)	3.62%	6.22%
Class S Shares Return Before Taxes	Class S Shares	Return Before Taxes		(3.69%)	4.36%	6.98%
Class I Shares Return Before Taxes	Class I Shares	Return Before Taxes		(3.28%)	4.60%	7.23%
Class N Shares Return Before Taxes	Class N Shares	Return Before Taxes		(3.43%)	4.60%	7.23%
Class R Shares Return Before Taxes	Class R Shares	Return Before Taxes		(3.89%)	4.10%	6.72%
Russell 2000 Value Index (reflects no deduction for expenses, fees, or taxes)		Russell 2000® Value Index		(5.50%)	(1.87%)	6.40%

After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares) for the periods following April 21, 2003; and for Berger Small Cap Value Fund – Investor Shares for periods prior to April 21, 2003. If Class T Shares of the Fund had been available during the periods prior to April 21, 2003, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

[1] Other Expenses for Class N Shares are based on the estimated expenses that the Shares expect to incur during their initial fiscal period.

[2] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding any performance adjustments to management fees, the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, Class S Shares, and Class R Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 0.96% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Janus Growth Allocation Fund | Class A, C, S, I, T Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Janus Growth Allocation Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Janus Growth Allocation Fund seeks total return through a primary emphasis on growth of capital with a secondary emphasis on income.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

SHAREHOLDER FEES
(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 18% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

18.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 45 of the Fund’s Prospectus and in the “Purchases” section on page 63 of the Fund’s Statement of Additional Information.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses (including the operating expenses of the underlying funds) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

If Shares are redeemed:

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

If Shares are not redeemed:

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund seeks to achieve its investment objective by investing in other Janus mutual funds (“underlying funds”) that represent a variety of asset classes and investment styles. The Fund pursues this objective by investing in a diversified portfolio of underlying funds resulting in an allocation of the Fund’s investments that normally provides exposure of approximately 80% to stocks and 20% to bonds and money market securities. The target allocation and the allocation of the Fund’s assets among underlying funds are based on quantitative and qualitative analysis. Because it invests in other funds, the Fund is considered a “fund of funds.”

The Fund’s asset allocation is intended to diversify investments among stocks, bonds, and cash equivalents. The portfolio manager regularly reviews the allocation of Fund assets in the underlying funds and may modify the underlying funds’ weightings or substitute other underlying funds to emphasize and mitigate risk exposures that may arise as a result of the implementation of the allocations. An independent asset allocation service provides evaluations of asset allocations that the portfolio manager may use in implementing the allocations among the underlying funds. The portfolio manager continually monitors asset class allocations and periodically rebalances the Fund’s investments in the underlying funds. The portfolio manager may change the Fund’s asset class allocations, the underlying funds, an underlying fund’s asset category, or weightings among asset classes or underlying funds without prior shareholder notice.

The Fund will normally allocate approximately 80% of its investments to underlying funds that provide varying exposure to common stocks of large U.S.-based companies, small- to mid-capitalization companies, and international companies (including those with exposure to emerging markets); and approximately 20% of its investments to underlying bond funds and money market instruments. Refer to Appendix A in this Prospectus for a brief description of the investment strategies of each of the currently available underlying funds.

When market conditions dictate a more defensive strategy, the Fund or an underlying fund may temporarily hold cash or invest its assets in temporary investments. In that case, the Fund may take positions that are inconsistent with its investment objective. As a result, the Fund may not achieve its investment objective.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking growth of capital and, to a lesser extent, income. Investments in a portfolio with common stock exposure tend to be more volatile than many other investment choices.

Main Risks Associated with the Fund
Allocation Risk. The Fund’s ability to achieve its investment objective depends largely upon the portfolio manager’s allocation of assets among the underlying funds and other securities, using the optimization process (a process that utilizes quantitative analysis of a number of factors, such as historical risk, performance, fund classifications, and the relationship among underlying funds) and the judgment of the portfolio manager. You could lose money on your investment in the Fund as a result of these allocations. The Fund will typically invest in a number of different underlying funds; however, to the extent that the Fund invests a significant portion of its assets in a single underlying fund, it will be more sensitive to the risks associated with that fund and any investments in which that fund concentrates.

Affiliated Fund Risk. Janus Capital has the authority to select and substitute underlying affiliated mutual funds. The fees paid to Janus Capital by some Janus mutual funds are generally higher than the fees paid to Janus Capital by the Fund or by other funds and share classes available for investment by the Fund. These conditions may create a conflict of interest when selecting underlying affiliated mutual funds and share classes for investment. Janus Capital, however, is a fiduciary to the Fund and its shareholders and is legally obligated to act in their best interest when selecting underlying affiliated mutual funds.

Main Risks Associated with the Underlying Funds and Securities
The biggest risk is that the underlying funds’ returns will vary, and you could lose money.

Market Risk. Approximately 80% of the Fund’s assets are allocated to equity investments through investments in underlying funds. The value of an underlying fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if a portfolio manager’s belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of an underlying fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Fixed-Income Securities Risk. Approximately 20% of the Fund’s assets are allocated to fixed-income securities through investments in underlying funds. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause an underlying fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which an underlying fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that an underlying fund’s portfolio manager would like or at the price that the portfolio manager believes the security is currently worth.

Foreign Exposure Risk. Certain underlying funds may have significant exposure to foreign markets as a result of their investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, an underlying fund’s returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. A market swing in one or more countries or regions where an underlying fund has invested a significant amount of its assets may have a greater effect on an underlying fund’s performance than it would in a more geographically diversified portfolio. An underlying fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Emerging Markets Risk. The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities involve a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. In addition, an underlying fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of an underlying fund’s investments. To the extent that an underlying fund invests a significant portion of its assets in the securities of issuers in or companies of a single country or region, it is more likely to be impacted by events or conditions affecting that country or region, which could have a negative impact on the Fund’s performance. Some of the risks of investing directly in foreign and emerging market securities may be reduced when an underlying fund invests indirectly in foreign securities through various other investment vehicles including derivatives, which also involve other risks.

Sovereign Debt Risk. An underlying fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Exchange-Traded Funds Risk. Certain underlying funds may purchase shares of exchange-traded funds (“ETFs”) to gain exposure to a particular portion of the market. ETFs are pooled investment vehicles, which may be managed or unmanaged, that generally seek to track the performance of a specific index. ETFs are traded on an exchange at market prices that may vary from the net asset value of their underlying investments. When an underlying fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF’s expenses. ETFs have certain inherent risks generally associated with investments in a portfolio of securities in which the ETF is invested, including the risk that the general level of stock prices may decline, thereby adversely affecting the value of each unit of the ETF. ETFs also involve the risk that an active trading market for an ETF’s shares may not develop or be maintained.

Exchange-Traded Notes Risk. Certain underlying funds may invest in exchange-traded notes (“ETNs”), which are debt securities whose returns are linked to a particular index. ETNs are typically linked to the performance of a commodities index that reflects the potential return on unleveraged investments in futures contracts of physical commodities, plus a specified rate of interest that could be earned on cash collateral. ETNs are subject to credit risk. The value of an ETN may vary and may be influenced by time to maturity, level of supply and demand for the ETN, volatility and lack of liquidity in underlying commodities markets, changes in the applicable interest rates, changes in the issuer’s credit rating, and economic, legal, political, or geographic events that affect the referenced commodity. When an underlying fund invests in ETNs it will bear its proportionate share of any fees and expenses borne by the ETN. There may be restrictions on an underlying fund’s right to redeem its investment in an ETN, which is meant to be held until maturity. An underlying fund’s decision to sell its ETN holdings may be limited by the availability of a secondary market.

Derivatives Risk. Certain underlying funds may invest in derivatives. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

The biggest risk is that the Fund’s returns will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares, the initial share class) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund commenced operations on July 6, 2009.

• The performance shown for Class T Shares is calculated using the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class A Shares, Class C Shares, and Class S Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers.
• The performance shown for Class I Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers.

If Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund had been available during periods prior to July 6, 2009, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, and Class I Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. Performance information for each underlying fund is available in its prospectus and/or the most recent annual or semiannual report. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-877-335-2687

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/advisor/mutual-funds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class T Shares (calendar year-end)

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Second Quarter 2009  18.37%          Worst Quarter:  Fourth Quarter 2008  −18.05%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 11.44%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The Growth Allocation Index is an internally-calculated, hypothetical combination of unmanaged indices that combines total returns from the Dow Jones Wilshire 5000 Index (50%), the MSCI EAFE^® Index (25%), the Barclays U.S. Aggregate Bond Index (20%), and the Morgan Stanley Capital International Emerging Markets Free Index^sm (5%).

After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares, the initial share class). After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Janus Growth Allocation Fund | Class A, C, S, I, T Shares | Class A

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class A

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class A

Management Fees

rr_ManagementFeesOverAssets

0.05%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.22%

^[1]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.76%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.28%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleYear01

698

3 Years

rr_ExpenseExampleYear03

958

5 Years

rr_ExpenseExampleYear05

1,237

10 Years

rr_ExpenseExampleYear10

2,031

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

698

3 Years

rr_ExpenseExampleNoRedemptionYear03

958

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,237

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,031

Janus Growth Allocation Fund | Class A, C, S, I, T Shares | Class C

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class C

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

1.00%

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class C

Management Fees

rr_ManagementFeesOverAssets

0.05%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

0.33%

^[1]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.76%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

2.14%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleYear01

317

3 Years

rr_ExpenseExampleYear03

670

5 Years

rr_ExpenseExampleYear05

1,149

10 Years

rr_ExpenseExampleYear10

2,472

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

217

3 Years

rr_ExpenseExampleNoRedemptionYear03

670

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,149

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,472

Janus Growth Allocation Fund | Class A, C, S, I, T Shares | Class S

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class S

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class S

Management Fees

rr_ManagementFeesOverAssets

0.05%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.36%

^[1]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.76%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.42%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleYear01

145

3 Years

rr_ExpenseExampleYear03

449

5 Years

rr_ExpenseExampleYear05

776

10 Years

rr_ExpenseExampleYear10

1,702

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

145

3 Years

rr_ExpenseExampleNoRedemptionYear03

449

5 Years

rr_ExpenseExampleNoRedemptionYear05

776

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,702

Janus Growth Allocation Fund | Class A, C, S, I, T Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class I

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class I

Management Fees

rr_ManagementFeesOverAssets

0.05%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.20%

^[1]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.76%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.01%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleYear01

103

3 Years

rr_ExpenseExampleYear03

322

5 Years

rr_ExpenseExampleYear05

558

10 Years

rr_ExpenseExampleYear10

1,236

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

103

3 Years

rr_ExpenseExampleNoRedemptionYear03

322

5 Years

rr_ExpenseExampleNoRedemptionYear05

558

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,236

Janus Growth Allocation Fund | Class A, C, S, I, T Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class T

Management Fees

rr_ManagementFeesOverAssets

0.05%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.37%

^[1]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.76%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.18%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleYear01

120

3 Years

rr_ExpenseExampleYear03

375

5 Years

rr_ExpenseExampleYear05

649

10 Years

rr_ExpenseExampleYear10

1,432

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

120

3 Years

rr_ExpenseExampleNoRedemptionYear03

375

5 Years

rr_ExpenseExampleNoRedemptionYear05

649

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,432

2006

rr_AnnualReturn2006

18.51%

2007

rr_AnnualReturn2007

15.73%

2008

rr_AnnualReturn2008

(34.91%)

2009

rr_AnnualReturn2009

35.79%

2010

rr_AnnualReturn2010

13.40%

2011

rr_AnnualReturn2011

(6.49%)

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

11.44%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

18.37%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(18.05%)

Janus Growth Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class A

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class A Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[2]

1 Year

rr_AverageAnnualReturnYear01

(11.93%)

5 Years

rr_AverageAnnualReturnYear05

0.30%

Since Inception

rr_AverageAnnualReturnSinceInception

3.10%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Growth Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class C

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class C Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[3]

1 Year

rr_AverageAnnualReturnYear01

(8.17%)

5 Years

rr_AverageAnnualReturnYear05

0.75%

Since Inception

rr_AverageAnnualReturnSinceInception

3.35%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Growth Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class S

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class S Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(6.79%)

5 Years

rr_AverageAnnualReturnYear05

1.27%

Since Inception

rr_AverageAnnualReturnSinceInception

3.88%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Growth Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(6.38%)

5 Years

rr_AverageAnnualReturnYear05

1.64%

Since Inception

rr_AverageAnnualReturnSinceInception

4.27%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Growth Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(6.49%)

5 Years

rr_AverageAnnualReturnYear05

1.64%

Since Inception

rr_AverageAnnualReturnSinceInception

4.27%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Growth Allocation Fund | Class A, C, S, I, T Shares | Return After Taxes on Distributions | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

(6.91%)

5 Years

rr_AverageAnnualReturnYear05

1.01%

Since Inception

rr_AverageAnnualReturnSinceInception

3.66%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Growth Allocation Fund | Class A, C, S, I, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[4]

1 Year

rr_AverageAnnualReturnYear01

(4.07%)

5 Years

rr_AverageAnnualReturnYear05

1.13%

Since Inception

rr_AverageAnnualReturnSinceInception

3.42%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Growth Allocation Fund | Class A, C, S, I, T Shares | S&P 500 Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

S&P 500^® Index

1 Year

rr_AverageAnnualReturnYear01

2.11%

5 Years

rr_AverageAnnualReturnYear05

(0.25%)

Since Inception

rr_AverageAnnualReturnSinceInception

2.26%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Growth Allocation Fund | Class A, C, S, I, T Shares | Growth Allocation Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Growth Allocation Index

1 Year

rr_AverageAnnualReturnYear01

(2.07%)

5 Years

rr_AverageAnnualReturnYear05

0.80%

Since Inception

rr_AverageAnnualReturnSinceInception

3.31%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

[1] Other Expenses are based on the estimated expenses that the Fund expects to incur.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

[4] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

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Oct. 26, 2012

Janus Money Market Fund | Class T Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

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Fund summary

Janus Money Market Fund

Objective [Heading]

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INVESTMENT OBJECTIVES

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Janus Money Market Fund seeks capital preservation and liquidity

Objective, Secondary [Text Block]

rr_ObjectiveSecondaryTextBlock

with current income as a secondary objective.

Expense [Heading]

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FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

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This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

Operating Expenses Caption [Text]

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ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Expense Example [Heading]

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EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

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The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Strategy [Heading]

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PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

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The Fund pursues its investment objectives by investing primarily in high quality debt obligations and obligations of financial institutions. Debt obligations may include commercial paper, notes and bonds, and variable amount master demand notes. Obligations of financial institutions include certificates of deposit and time deposits. The Fund also intends to invest in repurchase agreements including those secured by U.S. Government agencies. Some government agencies backed by the full faith and credit of the United States are supported by the issuer’s ability to borrow from the United States Treasury, some are supported only by the credit of the issuer, and some are supported by the United States in some other way.

The Fund will:

• invest in high quality, short-term money market instruments that present minimal credit risks, as determined by Janus Capital

• invest only in U.S. dollar-denominated instruments that have a remaining maturity of 397 days or less (as calculated pursuant to Rule 2a-7 under the Investment Company Act of 1940, as amended)

• maintain a dollar-weighted average portfolio maturity of 60 days or less and maintain a dollar-weighted average portfolio life (portfolio maturity measured without reference to any maturity shortening provisions of adjustable rate securities by reference to their interest rate reset dates) of 120 days or less

Risk [Heading]

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PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

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Market Risk. The Fund’s yield will vary as the short-term securities in its portfolio mature and the proceeds are reinvested in securities with different interest rates. For capital preservation and liquidity, the Fund may have a greater concentration in short-term securities including, but not limited to, investing up to all of its assets in overnight securities, which may result in a reduction of the Fund’s yield. Over time, the real value of the Fund’s yield may be eroded by inflation. Although the Fund invests only in high-quality, short-term money market instruments, there is a risk that the value of the securities it holds will fall as a result of changes in interest rates, an issuer’s actual or perceived creditworthiness, or an issuer’s ability to meet its obligations. The credit quality of the Fund’s holdings can change rapidly in certain market environments and any downgrade or default of a portfolio security could cause the Fund’s share price or yield to fall.

Collateral Risk. With respect to collateral received in repurchase transactions or other investments, the Fund may have significant exposure to financial services, mortgage markets, and government agencies not secured by the full faith and credit of the United States. Such exposure, depending on market conditions, could have a negative impact on the Fund, including minimizing the value of any collateral.

Money Market Risk. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund.

Risk Money Market Fund [Text]

rr_RiskMoneyMarketFund

Money Market Risk. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund.

Bar Chart and Performance Table [Heading]

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PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares, the initial share class) of the Fund commenced operations with the Fund’s inception. The performance shown for Class T Shares is calculated using the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table shows how the Fund’s returns over different periods average out. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-877-335-2687

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/advisor/mutual-funds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

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Annual Total Returns for Class T Shares (calendar year-end)

Bar Chart Closing [Text Block]

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Best Quarter:  Fourth Quarter 2006  1.23%     Worst Quarter:  Third Quarter 2011  0.00%

Year to Date Return, Label

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The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 0.00%.

Performance Table Heading

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Average Annual Total Returns (periods ended 12/31/11)

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Money Market Seven Day Yield, Caption [Text]

rr_MoneyMarketSevenDayYieldCaption

The 7-day yield on December 31, 2011 was 0.01% for Janus Money Market Fund.

Money Market Seven Day Yield

rr_MoneyMarketSevenDayYield

0.01%

Janus Money Market Fund | Class T Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class T

Management Fees

rr_ManagementFeesOverAssets

0.20%

Other Expenses

rr_OtherExpensesOverAssets

0.49%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.69%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleYear01

70

3 Years

rr_ExpenseExampleYear03

221

5 Years

rr_ExpenseExampleYear05

384

10 Years

rr_ExpenseExampleYear10

859

2002

rr_AnnualReturn2002

1.38%

2003

rr_AnnualReturn2003

0.71%

2004

rr_AnnualReturn2004

0.93%

2005

rr_AnnualReturn2005

2.77%

2006

rr_AnnualReturn2006

4.60%

2007

rr_AnnualReturn2007

4.86%

2008

rr_AnnualReturn2008

2.09%

2009

rr_AnnualReturn2009

0.07%

2010

rr_AnnualReturn2010

0.01%

2011

rr_AnnualReturn2011

0.01%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

0.00%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Dec. 31, 2006

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

1.23%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

0.00%

Janus Money Market Fund | Class T Shares | Return Before Taxes | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

0.01%

5 Years

rr_AverageAnnualReturnYear05

1.39%

10 Years

rr_AverageAnnualReturnYear10

1.73%

Since Inception

rr_AverageAnnualReturnSinceInception

3.08%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 14, 1995

XML

INTECH U.S. Core Fund | Class A, C, S, I, T Shares

Fund summary

INTECH U.S. Core Fund

INVESTMENT OBJECTIVE

INTECH U.S. Core Fund seeks long-term growth of capital.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 46 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.

SHAREHOLDER FEES
(fees paid directly from your investment)

Shareholder Fees INTECH U.S. Core Fund Class A, C, S, I, T Shares	Class A	Class C	Class S	Class I	Class T
Shareholder Fees Column [Text]	Class A	Class C	Class S	Class I	Class T
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	5.75%	none	none	none	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	none	1.00%	none	none	none

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses INTECH U.S. Core Fund Class A, C, S, I, T Shares	Class A	Class C	Class S	Class I	Class T
Operating Expenses Column [Text]	Class A	Class C	Class S	Class I	Class T
Management Fees (may adjust up or down)	0.54%	0.54%	0.54%	0.54%	0.54%
Distribution/Service (12b-1) Fees	0.25%	1.00%	0.25%	none	none
Other Expenses	0.20%	0.29%	0.37%	0.18%	0.37%
Total Annual Fund Operating Expenses	0.99%	1.83%	1.16%	0.72%	0.91%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

If Shares are redeemed:

Expense Example INTECH U.S. Core Fund Class A, C, S, I, T Shares (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	670	872	1,091	1,718
Class C	Class C Shares	286	576	990	2,148
Class S	Class S Shares	118	368	638	1,409
Class I	Class I Shares	74	230	401	894
Class T	Class T Shares	93	290	504	1,120

If Shares are not redeemed:

Expense Example, No Redemption INTECH U.S. Core Fund Class A, C, S, I, T Shares (USD $)	Expense Example, No Redemption, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	670	872	1,091	1,718
Class C	Class C Shares	186	576	990	2,148
Class S	Class S Shares	118	368	638	1,409
Class I	Class I Shares	74	230	401	894
Class T	Class T Shares	93	290	504	1,120

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 73% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund invests, under normal circumstances, at least 80% of its net assets in U.S. common stocks from the universe of the S&P 500^® Index, utilizing INTECH’s mathematical investment process. The S&P 500^® Index is an unmanaged index of 500 stocks that is generally representative of the performance of larger companies in the United States.

The Fund pursues its investment objective by applying a mathematical investment process to construct an investment portfolio from the universe of common stocks within its named benchmark index. The goal of this process is to build a portfolio of stocks in a more efficient combination than the named benchmark index. The process seeks to capitalize on the natural volatility of the market by searching for stocks within the index that have high relative volatility (providing the potential for excess returns) but that essentially move in opposite directions or have low correlation to each other (providing the potential for lower relative risk). By constructing the portfolio in this manner and periodically rebalancing the portfolio to maintain potentially more efficient weightings, INTECH’s mathematical investment process seeks to create a portfolio that, over time, produces returns in excess of its named benchmark index with risks similar to that of the benchmark index. The rebalancing techniques used by INTECH may result in a higher portfolio turnover compared to a “buy and hold” fund strategy.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Investment Process Risk. The proprietary mathematical investment process used by INTECH may not achieve the desired results. On an occasional basis, INTECH considers changes to its mathematical investment process. These changes may result in changes to the portfolio, might not provide the intended results, and may adversely impact the Fund’s performance.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares, the initial share class) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund commenced operations on July 6, 2009.

•   The performance shown for Class T Shares is calculated using the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers.
•   The performance shown for Class A Shares, Class C Shares, and Class S Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers.
•   The performance shown for Class I Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers.

If Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund had been available during periods prior to July 6, 2009, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, and Class I Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Annual Total Returns for Class T Shares (calendar year-end)

Best Quarter:  Second Quarter 2009  14.79%     Worst Quarter:   Fourth Quarter 2008  −21.49%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 14.92%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns INTECH U.S. Core Fund Class A, C, S, I, T Shares	Column	Label		1 Year	5 Years	Since Inception	Inception Date
Class T Shares Return Before Taxes	Class T Shares	Return Before Taxes		4.97%	0.25%	7.79%	Feb. 28, 2003
Class T Shares Return After Taxes on Distributions	Class T Shares	Return After Taxes on Distributions		4.83%	(0.23%)	7.07%	Feb. 28, 2003
Class T Shares Return After Taxes on Distributions and Sale of Fund Shares	Class T Shares	Return After Taxes on Distributions and Sale of Fund Shares	[1]	3.42%	0.18%	6.72%	Feb. 28, 2003
Class A Shares Return Before Taxes	Class A Shares	Return Before Taxes	[2]	(1.16%)	(1.16%)	6.78%	Feb. 28, 2003
Class C Shares Return Before Taxes	Class C Shares	Return Before Taxes	[3]	2.99%	(0.72%)	6.71%	Feb. 28, 2003
Class S Shares Return Before Taxes	Class S Shares	Return Before Taxes		4.71%	(0.14%)	7.31%	Feb. 28, 2003
Class I Shares Return Before Taxes	Class I Shares	Return Before Taxes		5.18%	0.25%	7.79%	Feb. 28, 2003
S&P 500 Index (reflects no deduction for expenses, fees, or taxes)		S&P 500® Index		2.11%	(0.25%)	6.77%	Feb. 28, 2003

After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares, the initial share class). After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Janus High-Yield Fund | Class A, C, S, I, N, R, T Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Janus High-Yield Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVES

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Janus High-Yield Fund seeks to obtain high current income.

Objective, Secondary [Text Block]

rr_ObjectiveSecondaryTextBlock

Capital appreciation is a secondary investment objective when consistent with its primary investment objective.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

SHAREHOLDER FEES
(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 61% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

61.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 51 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

If Shares are redeemed:

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

If Shares are not redeemed:

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund pursues its investment objectives by investing, under normal circumstances, at least 80% of its net assets in high-yield/high-risk securities rated below investment grade. Securities rated below investment grade may include their unrated equivalents or other high-yielding securities the portfolio managers believe offer attractive risk/return characteristics. The Fund may at times invest all of its assets in such securities. The Fund may also invest in bank loans, money market instruments, and foreign debt securities (which may include investments in emerging markets). Due to the nature of securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

In addition, the Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. In particular, the Fund may use interest rate futures to manage portfolio risk. The Fund’s exposure to derivatives will vary. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

In addition to considering economic factors such as the effect of interest rates on the Fund’s investments, the portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income‒producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

High-Yield/High-Risk Bond Risk. The Fund may invest without limit in higher-yielding/higher-risk bonds, also known as “junk” bonds. High-yield/high-risk bonds may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Bank Loan Risk. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. Participation interests and assignments involve credit, interest rate, and liquidity risk. In addition, the bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. To the extent the Fund invests in foreign debt securities, such investments are sensitive to changes in interest rates. Additionally, investments in securities of foreign governments involve the risk that a foreign government may not be willing or able to pay interest or repay principal when due. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares, the initial share class) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class R Shares of the Fund commenced operations on July 6, 2009. Class N Shares of the Fund commenced operations on May 31, 2012.

• The performance shown for Class T Shares is calculated using the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class A Shares, Class C Shares, Class S Shares, and Class R Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers.
• The performance shown for Class I Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class N Shares for periods prior to December 31, 2011, reflects the performance of the Fund’s Class T Shares, calculated using the fees and expenses of Class T Shares, net of any applicable fee and expense limitations or waivers.

If Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class R Shares of the Fund had been available during periods prior to July 6, 2009, or Class N Shares of the Fund had been available during periods prior to December 31, 2011, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, Class I Shares, Class N Shares, and Class R Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-877-335-2687

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/advisor/mutual-funds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class T Shares (calendar year-end)

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Second Quarter 2009  14.93%          Worst Quarter:  Fourth Quarter 2008   −12.96%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 10.73%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares, the initial share class). After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Janus High-Yield Fund | Class A, C, S, I, N, R, T Shares | Class A

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class A

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

4.75%

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class A

Management Fees

rr_ManagementFeesOverAssets

0.57%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.17%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.99%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleYear01

571

3 Years

rr_ExpenseExampleYear03

775

5 Years

rr_ExpenseExampleYear05

996

10 Years

rr_ExpenseExampleYear10

1,630

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

571

3 Years

rr_ExpenseExampleNoRedemptionYear03

775

5 Years

rr_ExpenseExampleNoRedemptionYear05

996

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,630

Janus High-Yield Fund | Class A, C, S, I, N, R, T Shares | Class C

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class C

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

1.00%

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class C

Management Fees

rr_ManagementFeesOverAssets

0.57%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

0.15%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.72%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleYear01

275

3 Years

rr_ExpenseExampleYear03

542

5 Years

rr_ExpenseExampleYear05

933

10 Years

rr_ExpenseExampleYear10

2,030

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

175

3 Years

rr_ExpenseExampleNoRedemptionYear03

542

5 Years

rr_ExpenseExampleNoRedemptionYear05

933

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,030

Janus High-Yield Fund | Class A, C, S, I, N, R, T Shares | Class S

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class S

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class S

Management Fees

rr_ManagementFeesOverAssets

0.57%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.29%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.11%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleYear01

113

3 Years

rr_ExpenseExampleYear03

353

5 Years

rr_ExpenseExampleYear05

612

10 Years

rr_ExpenseExampleYear10

1,352

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

113

3 Years

rr_ExpenseExampleNoRedemptionYear03

353

5 Years

rr_ExpenseExampleNoRedemptionYear05

612

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,352

Janus High-Yield Fund | Class A, C, S, I, N, R, T Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class I

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class I

Management Fees

rr_ManagementFeesOverAssets

0.57%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.11%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.68%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleYear01

69

3 Years

rr_ExpenseExampleYear03

218

5 Years

rr_ExpenseExampleYear05

379

10 Years

rr_ExpenseExampleYear10

847

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

69

3 Years

rr_ExpenseExampleNoRedemptionYear03

218

5 Years

rr_ExpenseExampleNoRedemptionYear05

379

10 Years

rr_ExpenseExampleNoRedemptionYear10

847

Janus High-Yield Fund | Class A, C, S, I, N, R, T Shares | Class N

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class N

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class N

Management Fees

rr_ManagementFeesOverAssets

0.57%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.04%

^[1]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.61%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class N Shares

1 Year

rr_ExpenseExampleYear01

62

3 Years

rr_ExpenseExampleYear03

195

5 Years

rr_ExpenseExampleYear05

340

10 Years

rr_ExpenseExampleYear10

762

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class N Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

62

3 Years

rr_ExpenseExampleNoRedemptionYear03

195

5 Years

rr_ExpenseExampleNoRedemptionYear05

340

10 Years

rr_ExpenseExampleNoRedemptionYear10

762

Janus High-Yield Fund | Class A, C, S, I, N, R, T Shares | Class R

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class R

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class R

Management Fees

rr_ManagementFeesOverAssets

0.57%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.50%

Other Expenses

rr_OtherExpensesOverAssets

0.29%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.36%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class R Shares

1 Year

rr_ExpenseExampleYear01

138

3 Years

rr_ExpenseExampleYear03

431

5 Years

rr_ExpenseExampleYear05

745

10 Years

rr_ExpenseExampleYear10

1,635

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class R Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

138

3 Years

rr_ExpenseExampleNoRedemptionYear03

431

5 Years

rr_ExpenseExampleNoRedemptionYear05

745

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,635

Janus High-Yield Fund | Class A, C, S, I, N, R, T Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class T

Management Fees

rr_ManagementFeesOverAssets

0.57%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.29%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.86%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleYear01

88

3 Years

rr_ExpenseExampleYear03

274

5 Years

rr_ExpenseExampleYear05

477

10 Years

rr_ExpenseExampleYear10

1,061

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

88

3 Years

rr_ExpenseExampleNoRedemptionYear03

274

5 Years

rr_ExpenseExampleNoRedemptionYear05

477

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,061

2002

rr_AnnualReturn2002

2.56%

2003

rr_AnnualReturn2003

16.04%

2004

rr_AnnualReturn2004

9.42%

2005

rr_AnnualReturn2005

2.77%

2006

rr_AnnualReturn2006

11.10%

2007

rr_AnnualReturn2007

1.35%

2008

rr_AnnualReturn2008

(19.32%)

2009

rr_AnnualReturn2009

40.86%

2010

rr_AnnualReturn2010

15.72%

2011

rr_AnnualReturn2011

3.20%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

10.73%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

14.93%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(12.96%)

Janus High-Yield Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class A

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class A Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[2]

1 Year

rr_AverageAnnualReturnYear01

(1.71%)

5 Years

rr_AverageAnnualReturnYear05

5.45%

10 Years

rr_AverageAnnualReturnYear10

6.82%

Since Inception

rr_AverageAnnualReturnSinceInception

7.46%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 29, 1995

Janus High-Yield Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class C

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class C Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[3]

1 Year

rr_AverageAnnualReturnYear01

1.37%

5 Years

rr_AverageAnnualReturnYear05

5.74%

10 Years

rr_AverageAnnualReturnYear10

6.59%

Since Inception

rr_AverageAnnualReturnSinceInception

7.02%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 29, 1995

Janus High-Yield Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class S

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class S Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

2.95%

5 Years

rr_AverageAnnualReturnYear05

6.30%

10 Years

rr_AverageAnnualReturnYear10

7.12%

Since Inception

rr_AverageAnnualReturnSinceInception

7.56%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 29, 1995

Janus High-Yield Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

3.36%

5 Years

rr_AverageAnnualReturnYear05

6.58%

10 Years

rr_AverageAnnualReturnYear10

7.42%

Since Inception

rr_AverageAnnualReturnSinceInception

7.83%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 29, 1995

Janus High-Yield Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class N

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class N Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

3.20%

5 Years

rr_AverageAnnualReturnYear05

6.58%

10 Years

rr_AverageAnnualReturnYear10

7.42%

Since Inception

rr_AverageAnnualReturnSinceInception

7.83%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 29, 1995

Janus High-Yield Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class R

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class R Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

2.74%

5 Years

rr_AverageAnnualReturnYear05

6.01%

10 Years

rr_AverageAnnualReturnYear10

6.85%

Since Inception

rr_AverageAnnualReturnSinceInception

7.29%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 29, 1995

Janus High-Yield Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

3.20%

5 Years

rr_AverageAnnualReturnYear05

6.58%

10 Years

rr_AverageAnnualReturnYear10

7.42%

Since Inception

rr_AverageAnnualReturnSinceInception

7.83%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 29, 1995

Janus High-Yield Fund | Class A, C, S, I, N, R, T Shares | Return After Taxes on Distributions | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes On Distributions

1 Year

rr_AverageAnnualReturnYear01

0.64%

5 Years

rr_AverageAnnualReturnYear05

3.38%

10 Years

rr_AverageAnnualReturnYear10

4.48%

Since Inception

rr_AverageAnnualReturnSinceInception

4.55%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 29, 1995

Janus High-Yield Fund | Class A, C, S, I, N, R, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes On Distributions and Sale of Fund Shares

^[4]

1 Year

rr_AverageAnnualReturnYear01

2.07%

5 Years

rr_AverageAnnualReturnYear05

3.65%

10 Years

rr_AverageAnnualReturnYear10

4.56%

Since Inception

rr_AverageAnnualReturnSinceInception

4.65%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 29, 1995

Janus High-Yield Fund | Class A, C, S, I, N, R, T Shares | Barclays U.S. Corporate High-Yield Bond Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Barclays U.S. Corporate High-Yield Bond Index

1 Year

rr_AverageAnnualReturnYear01

4.98%

5 Years

rr_AverageAnnualReturnYear05

7.54%

10 Years

rr_AverageAnnualReturnYear10

8.85%

Since Inception

rr_AverageAnnualReturnSinceInception

7.18%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 29, 1995

[1] Other Expenses for Class N Shares are based on the estimated expenses that the Shares expect to incur during their initial fiscal period.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

[4] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Janus Moderate Allocation Fund | Class D Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Janus Moderate Allocation Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Janus Moderate Allocation Fund seeks total return through growth of capital and income.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 18% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

18.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses (including the operating expenses of the underlying funds) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund seeks to achieve its investment objective by investing in other Janus mutual funds (“underlying funds”) that represent a variety of asset classes and investment styles. The Fund pursues this objective by investing in a diversified portfolio of underlying funds resulting in an allocation of the Fund’s investments that normally provides exposure of approximately 60% to stocks and 40% to bonds and money market securities. The target allocation and the allocation of the Fund’s assets among underlying funds are based on quantitative and qualitative analysis. Because it invests in other funds, the Fund is considered a “fund of funds.”

The Fund’s asset allocation is intended to diversify investments among stocks, bonds, and cash equivalents. The portfolio manager regularly reviews the allocation of Fund assets in the underlying funds and may modify the underlying funds’ weightings or substitute other underlying funds to emphasize and mitigate risk exposures that may arise as a result of the implementation of the allocations. An independent asset allocation service provides evaluations of asset allocations that the portfolio manager may use in implementing the allocations among the underlying funds. The portfolio manager continually monitors asset class allocations and periodically rebalances the Fund’s investments in the underlying funds. The portfolio manager may change the Fund’s asset class allocations, the underlying funds, an underlying fund’s asset category, or weightings among asset classes or underlying funds without prior shareholder notice.

The Fund will normally allocate approximately 60% of its investments to underlying funds that provide varying exposure to common stocks of large U.S.-based companies, small- to mid-capitalization companies, and international companies (including those with exposure to emerging markets); and approximately 40% of its investments to underlying bond funds and money market instruments. Refer to Appendix A in this Prospectus for a brief description of the investment strategies of each of the currently available underlying funds.

When market conditions dictate a more defensive strategy, the Fund or an underlying fund may temporarily hold cash or invest its assets in temporary investments. In that case, the Fund may take positions that are inconsistent with its investment objective. As a result, the Fund may not achieve its investment objective.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking growth of capital and income. Investments in a portfolio with common stock exposure tend to be more volatile than many other investment choices.

Main Risks Associated with the Fund
Allocation Risk. The Fund’s ability to achieve its investment objective depends largely upon the portfolio manager’s allocation of assets among the underlying funds and other securities, using the optimization process (a process that utilizes quantitative analysis of a number of factors, such as historical risk, performance, fund classifications, and the relationship among underlying funds) and the judgment of the portfolio manager. You could lose money on your investment in the Fund as a result of these allocations. The Fund will typically invest in a number of different underlying funds; however, to the extent that the Fund invests a significant portion of its assets in a single underlying fund, it will be more sensitive to the risks associated with that fund and any investments in which that fund concentrates.

Affiliated Fund Risk. Janus Capital has the authority to select and substitute underlying affiliated mutual funds. The fees paid to Janus Capital by some Janus mutual funds are generally higher than the fees paid to Janus Capital by the Fund or by other funds and share classes available for investment by the Fund. These conditions may create a conflict of interest when selecting underlying affiliated mutual funds and share classes for investment. Janus Capital, however, is a fiduciary to the Fund and its shareholders and is legally obligated to act in their best interest when selecting underlying affiliated mutual funds.

Main Risks Associated with the Underlying Funds and Securities
The biggest risk is that the underlying funds’ returns will vary, and you could lose money.

Market Risk. Approximately 60% of the Fund’s assets are allocated to equity investments through investments in underlying funds. The value of an underlying fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if a portfolio manager’s belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of an underlying fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Fixed-Income Securities Risk. Approximately 40% of the Fund’s assets are allocated to fixed-income securities through investments in underlying funds. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause an underlying fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which an underlying fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that an underlying fund’s portfolio manager would like or at the price that the portfolio manager believes the security is currently worth.

Foreign Exposure Risk. Certain underlying funds may have significant exposure to foreign markets as a result of their investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, an underlying fund’s returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. A market swing in one or more countries or regions where an underlying fund has invested a significant amount of its assets may have a greater effect on an underlying fund’s performance than it would in a more geographically diversified portfolio. An underlying fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Emerging Markets Risk. The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities involve a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. In addition, an underlying fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of an underlying fund’s investments. To the extent that an underlying fund invests a significant portion of its assets in the securities of issuers in or companies of a single country or region, it is more likely to be impacted by events or conditions affecting that country or region, which could have a negative impact on the Fund’s performance. Some of the risks of investing directly in foreign and emerging market securities may be reduced when an underlying fund invests indirectly in foreign securities through various other investment vehicles including derivatives, which also involve other risks.

Sovereign Debt Risk. An underlying fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Exchange-Traded Funds Risk. Certain underlying funds may purchase shares of exchange-traded funds (“ETFs”) to gain exposure to a particular portion of the market. ETFs are pooled investment vehicles, which may be managed or unmanaged, that generally seek to track the performance of a specific index. ETFs are traded on an exchange at market prices that may vary from the net asset value of their underlying investments. When an underlying fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF’s expenses. ETFs have certain inherent risks generally associated with investments in a portfolio of securities in which the ETF is invested, including the risk that the general level of stock prices may decline, thereby adversely affecting the value of each unit of the ETF. ETFs also involve the risk that an active trading market for an ETF’s shares may not develop or be maintained.

Exchange-Traded Notes Risk. Certain underlying funds may invest in exchange-traded notes (“ETNs”), which are debt securities whose returns are linked to a particular index. ETNs are typically linked to the performance of a commodities index that reflects the potential return on unleveraged investments in futures contracts of physical commodities, plus a specified rate of interest that could be earned on cash collateral. ETNs are subject to credit risk. The value of an ETN may vary and may be influenced by time to maturity, level of supply and demand for the ETN, volatility and lack of liquidity in underlying commodities markets, changes in the applicable interest rates, changes in the issuer’s credit rating, and economic, legal, political, or geographic events that affect the referenced commodity. When an underlying fund invests in ETNs it will bear its proportionate share of any fees and expenses borne by the ETN. There may be restrictions on an underlying fund’s right to redeem its investment in an ETN, which is meant to be held until maturity. An underlying fund’s decision to sell its ETN holdings may be limited by the availability of a secondary market.

Derivatives Risk. Certain underlying funds may invest in derivatives. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

The biggest risk is that the Fund’s returns will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares, the predecessor share class. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses in effect during the periods shown, net of any applicable fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. Performance information for each underlying fund is available in its prospectus and/or the most recent annual or semiannual report. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-800-525-3713

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/allfunds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class D Shares (calendar year-end)

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter: Second Quarter 2009 14.27%     Worst Quarter: Fourth Quarter 2008 −11.62%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 10.34%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The Moderate Allocation Index is an internally-calculated, hypothetical combination of unmanaged indices that combines total returns from the Dow Jones Wilshire 5000 Index (40%), the Barclays U.S. Aggregate Bond Index (40%), the MSCI EAFE^® Index (18%), and the Morgan Stanley Capital International Emerging Markets Free Index^sm (2%).

After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; and for the Fund’s Class J Shares, the predecessor share class, for the periods prior to February 16, 2010. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Janus Moderate Allocation Fund | Class D Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class D

Management Fees

rr_ManagementFeesOverAssets

0.05%

Other Expenses

rr_OtherExpensesOverAssets

0.24%

^[1]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.69%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.98%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class D Shares

1 Year

rr_ExpenseExampleYear01

100

3 Years

rr_ExpenseExampleYear03

312

5 Years

rr_ExpenseExampleYear05

542

10 Years

rr_ExpenseExampleYear10

1,201

2006

rr_AnnualReturn2006

14.28%

2007

rr_AnnualReturn2007

12.71%

2008

rr_AnnualReturn2008

(25.28%)

2009

rr_AnnualReturn2009

30.34%

2010

rr_AnnualReturn2010

12.31%

2011

rr_AnnualReturn2011

(2.55%)

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

10.34%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

14.27%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(11.62%)

Janus Moderate Allocation Fund | Class D Shares | Return Before Taxes | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(2.55%)

5 Years

rr_AverageAnnualReturnYear05

3.74%

Since Inception

rr_AverageAnnualReturnSinceInception

5.42%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Moderate Allocation Fund | Class D Shares | Return After Taxes on Distributions | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

(3.27%)

5 Years

rr_AverageAnnualReturnYear05

2.84%

Since Inception

rr_AverageAnnualReturnSinceInception

4.58%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Moderate Allocation Fund | Class D Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[2]

1 Year

rr_AverageAnnualReturnYear01

(1.53%)

5 Years

rr_AverageAnnualReturnYear05

2.74%

Since Inception

rr_AverageAnnualReturnSinceInception

4.24%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Moderate Allocation Fund | Class D Shares | S&P 500 Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

S&P 500^® Index

1 Year

rr_AverageAnnualReturnYear01

2.11%

5 Years

rr_AverageAnnualReturnYear05

(0.25%)

Since Inception

rr_AverageAnnualReturnSinceInception

2.26%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Moderate Allocation Fund | Class D Shares | Moderate Allocation Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Moderate Allocation Index

1 Year

rr_AverageAnnualReturnYear01

0.96%

5 Years

rr_AverageAnnualReturnYear05

2.43%

Since Inception

rr_AverageAnnualReturnSinceInception

4.16%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

[1] Other Expenses are based on the estimated expenses that the Fund expects to incur.

[2] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Janus Flexible Bond Fund | Class A, C, S, I, N, R, T Shares

Fund summary

Janus Flexible Bond Fund

INVESTMENT OBJECTIVE

Janus Flexible Bond Fund seeks to obtain maximum total return, consistent with preservation of capital.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 51 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.

SHAREHOLDER FEES
(fees paid directly from your investment)

Shareholder Fees Janus Flexible Bond Fund Class A, C, S, I, N, R, T Shares

Class A

Class C

Class S

Class I

Class N

Class R

Class T

Shareholder Fees Column [Text]

Class A

Class C

Class S

Class I

Class N

Class R

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

4.75%

none

none

none

none

none

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

none

1.00%

none

none

none

none

none

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Janus Flexible Bond Fund Class A, C, S, I, N, R, T Shares

Class A

Class C

Class S

Class I

Class N

Class R

Class T

Operating Expenses Column [Text]

Class A

Class C

Class S

Class I

Class N

Class R

Class T

Management Fees

0.41%

0.41%

0.41%

0.41%

0.41%

0.41%

0.41%

Distribution/Service (12b-1) Fees

0.25%

1.00%

0.25%

none

none

0.50%

none

Other Expenses

0.11%

0.14%

0.29%

0.14%

0.05%

^[1]

0.29%

0.29%

Total Annual Fund Operating Expenses

0.77%

1.55%

0.95%

0.55%

0.46%

1.20%

0.70%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

If Shares are redeemed:

Expense Example Janus Flexible Bond Fund Class A, C, S, I, N, R, T Shares (USD $)

Expense Example, By Year, Column [Text]

1 Year

3 Years

5 Years

10 Years

Class A

Class A Shares

550

709

883

1,384

Class C

Class C Shares

258

490

845

1,845

Class S

Class S Shares

97

303

525

1,166

Class I

Class I Shares

56

176

307

689

Class N

Class N Shares

47

148

258

579

Class R

Class R Shares

122

381

660

1,455

Class T

Class T Shares

72

224

390

871

If Shares are not redeemed:

Expense Example, No Redemption Janus Flexible Bond Fund Class A, C, S, I, N, R, T Shares (USD $)

Expense Example, No Redemption, By Year, Column [Text]

1 Year

3 Years

5 Years

10 Years

Class A

Class A Shares

550

709

883

1,384

Class C

Class C Shares

158

490

845

1,845

Class S

Class S Shares

97

303

525

1,166

Class I

Class I Shares

56

176

307

689

Class N

Class N Shares

47

148

258

579

Class R

Class R Shares

122

381

660

1,455

Class T

Class T Shares

72

224

390

871

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 126% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objective by primarily investing, under normal circumstances, at least 80% of its net assets in bonds. Bonds include, but are not limited to, government notes and bonds, corporate bonds, convertible bonds, mortgage-backed securities, and zero-coupon bonds. The Fund will invest at least 65% of its assets in investment grade debt securities. As of June 30, 2012, the Fund’s weighted average maturity was 7.9 years. The Fund will limit its investment in high-yield/high-risk bonds, also known as “junk bonds,” to 35% or less of its net assets. The Fund generates total return from a combination of current income and capital appreciation, but income is usually the dominant portion. The Fund may also invest in asset-backed securities, money market instruments, bank loans, and foreign debt securities (which may include investments in emerging markets). Due to the nature of the securities in which the Fund invests, it may have relatively high portfolio turnover compared to other Funds.

In addition, the Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. In particular, the Fund may use interest rate futures to manage portfolio risk. The Fund’s exposure to derivatives will vary. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

In addition to considering economic factors such as the effect of interest rates on the Fund’s investments, the portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income-producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

PRINCIPAL INVESTMENT RISKS

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Sovereign Debt Risk. The Fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However, investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

High-Yield/High-Risk Bond Risk. High-yield/high-risk bonds may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Bank Loan Risk. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. Participation interests and assignments involve credit, interest rate, and liquidity risk. In addition, the bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. To the extent the Fund invests in foreign debt securities, such investments are sensitive to changes in interest rates. Additionally, investments in securities of foreign governments involve the risk that a foreign government may not be willing or able to pay interest or repay principal when due. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares, the initial share class) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class R Shares of the Fund commenced operations on July 6, 2009. Class N Shares of the Fund commenced operations on May 31, 2012.

• The performance shown for Class T Shares is calculated using the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class A Shares, Class C Shares, Class S Shares, and Class R Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers.
• The performance shown for Class I Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class N Shares for periods prior to December 31, 2011, reflects the performance of the Fund’s Class T Shares, calculated using the fees and expenses of Class T Shares, net of any applicable fee and expense limitations or waivers.

If Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class R Shares of the Fund had been available during periods prior to July 6, 2009, or Class N Shares of the Fund had been available during periods prior to December 31, 2011, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, Class I Shares, Class N Shares, and Class R Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Annual Total Returns for Class T Shares (calendar year-end)

Best Quarter:  Third Quarter 2009  5.58%          Worst Quarter:  Second Quarter 2004  −2.99%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 7.11%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Janus Flexible Bond Fund Class A, C, S, I, N, R, T Shares

Column

Label

1 Year

5 Years

10 Years

Since Inception

Inception Date

Class T Shares Return Before Taxes

Class T Shares

Return Before Taxes

6.50%

7.77%

6.46%

7.54%

Jul. 07, 1987

Class T Shares Return After Taxes on Distributions

Class T Shares

Return After Taxes on Distributions

4.88%

5.92%

4.67%

4.92%

Jul. 07, 1987

Class T Shares Return After Taxes on Distributions and Sale of Fund Shares

Class T Shares

Return After Taxes on Distributions and Sale of Fund Shares

4.44%

5.61%

4.50%

4.87%

Jul. 07, 1987

Class A Shares Return Before Taxes

Class A Shares

Return Before Taxes

^[1]

1.38%

6.68%

5.92%

7.31%

Jul. 07, 1987

Class C Shares Return Before Taxes

Class C Shares

Return Before Taxes

^[2]

4.63%

6.98%

5.73%

6.85%

Jul. 07, 1987

Class S Shares Return Before Taxes

Class S Shares

Return Before Taxes

6.24%

7.54%

6.24%

7.38%

Jul. 07, 1987

Class I Shares Return Before Taxes

Class I Shares

Return Before Taxes

6.66%

7.77%

6.46%

7.54%

Jul. 07, 1987

Class N Shares Return Before Taxes

Class N Shares

Return Before Taxes

6.50%

7.77%

6.46%

7.54%

Jul. 07, 1987

Class R Shares Return Before Taxes

Class R Shares

Return Before Taxes

5.98%

7.27%

5.99%

7.12%

Jul. 07, 1987

Barclays U.S. Aggregate Bond Index (reflects no deduction for expenses, fees, or taxes)

Barclays U.S. Aggregate Bond Index

7.84%

6.50%

5.78%

7.34%

Jul. 07, 1987

After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares, the initial share class). After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

[1] Other Expenses for Class N Shares are based on the estimated expenses that the Shares expect to incur during their initial fiscal period.

[1] Calculated assuming maximum permitted sales loads.

[2] The one year return is calculated to include the contingent deferred sales charge.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Janus Global Bond Fund | Class A, C, S, I, N, T Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Janus Global Bond Fund

Objective [Heading]

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INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

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Janus Global Bond Fund seeks total return, consistent with preservation of capital.

Expense [Heading]

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FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

SHAREHOLDER FEES
(fees paid directly from your investment)

Operating Expenses Caption [Text]

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ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

November 1, 2013

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 222% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

222.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the "Purchases" section on page 51 of the Fund's Prospectus and in the "Purchases" section on page 83 of the Fund's Statement of Additional Information.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses without waivers or recoupments (if applicable) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

If Shares are redeemed:

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

If Shares are not redeemed:

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

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The Fund pursues its investment objective by investing, under normal circumstances, at least 80% of its net assets in bonds. Bonds include, but are not limited to, corporate bonds, government notes and bonds, convertible bonds, mortgage-backed securities, and zero-coupon bonds. The Fund invests in corporate debt securities of issuers in a number of different countries, which may include the United States. The Fund invests in securities of issuers located in developed and emerging market countries. The Fund may invest across all fixed-income sectors, including U.S. and non-U.S. government securities. The Fund’s investments may be denominated in local currency or U.S. dollar-denominated. The Fund may invest in debt securities with a range of maturities from short- to long-term. The Fund may invest up to 35% of its net assets in high-yield/high-risk debt securities. The Fund may also invest in preferred and common stock, money market instruments, municipal bonds, commercial and residential mortgage-backed securities, asset-backed securities, other securitized and structured debt products, private placements, and other investment companies, including exchange-traded funds (“ETFs”). The Fund may also invest in bank loans, euro-denominated obligations, buy backs or dollar rolls, when-issued securities, and reverse repurchase agreements. Due to the nature of securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

In addition, the Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices, as substitutes for securities in which the Fund invests. The Fund has invested in and is expected to continue to invest in collateralized forward foreign currency exchange contracts, futures, options, and swaps (including interest rate swaps, total return swaps, and credit default swaps) for hedging purposes (to offset risks associated with an investment, currency exposure, or market conditions) and to increase or decrease the Fund’s exposure to a particular market, to manage or adjust the risk profile of the Fund related to an investment or currency exposure, to adjust its currency exposure relative to its benchmark index, and to earn income and enhance returns. In particular, the Fund may use interest rate futures to manage portfolio risk. The Fund’s exposure to derivatives will vary, is not limited to those derivatives listed, and could be significant at times. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

In addition to considering economic factors such as the effect of interest rates on the Fund’s investments, the portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income-producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

Foreign Exposure Risk. The Fund normally has significant exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries. To the extent the Fund invests in foreign debt securities, such investments are sensitive to changes in interest rates. Additionally, investments in securities of foreign governments involve the risk that a foreign government may not be willing or able to pay interest or repay principal when due.

Eurozone Exposure Risk. The Fund’s investment may include certain securities that are denominated and traded in, or based on, the euro, the official currency of the Eurozone. European markets have recently experienced volatility and adverse trends due to concerns about economic downturns, rising government debt levels, and the possible default of government debt in several European countries, including Greece, Ireland, Italy, Portugal, and Spain. A default or debt restructuring by any European country would adversely impact holders of that country’s debt and worldwide sellers of credit default swaps linked to that country’s creditworthiness. These trends have adversely affected the value and exchange rate of the euro and may continue to significantly affect the economies of all European countries, which in turn may have a material adverse affect on a Fund’s investments in such countries, other countries that depend on European countries for significant amounts of trade or investment, or issuers with exposure to European debt.

Emerging Markets Risk. The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities involve a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. There is a risk in developing countries that a future economic or political crisis could lead to price controls, forced mergers of companies, expropriation or confiscatory taxation, seizure, nationalization, or creation of government monopolies, any of which may have a detrimental effect on the Fund’s investments. In addition, the Fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of the Fund’s investments. To the extent that the Fund invests a significant portion of its assets in the securities of issuers in or companies of a single country or region, it is more likely to be impacted by events or conditions affecting that country or region, which could have a negative impact on the Fund’s performance. Some of the risks of investing directly in foreign and emerging market securities may be reduced when the Fund invests indirectly in foreign securities through various other investment vehicles including derivatives, which also involve other risks. As of June 30, 2012, approximately 10.1% of the Fund’s investments were in emerging markets.

Sovereign Debt Risk. The Fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However, investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner. A sovereign debtor’s willingness or ability to satisfy its debt obligation may be affected by various factors including, but not limited to, its cash flow situation, the extent of its foreign currency reserves, the availability of foreign exchange when a payment is due, and the relative size of its debt position in relation to its economy as a whole. In the event of default, there may be limited or no legal remedies for collecting sovereign debt and there may be no bankruptcy proceedings through which the Fund may collect all or part of the sovereign debt that a governmental entity has not repaid.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

High-Yield/High-Risk Bond Risk. High-yield/high-risk bonds (also known as “junk bonds”) may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Bank Loan Risk. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. Participation interests and assignments involve credit, interest rate, and liquidity risk. In addition, the bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings.

Exchange-Traded Funds Risk. The Fund may purchase shares of exchange-traded funds (“ETFs”) to gain exposure to a particular portion of the market. ETFs are pooled investment vehicles, which may be managed or unmanaged, that generally seek to track the performance of a specific index. ETFs are traded on an exchange at market prices that may vary from the net asset value of their underlying investments. When the Fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF’s expenses. ETFs have certain inherent risks generally associated with investments in a portfolio of securities in which the ETF is invested, including the risk that the general level of stock prices may decline, thereby adversely affecting the value of each unit of the ETF. ETFs also involve the risk that an active trading market for an ETF’s shares may not develop or be maintained.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund's performance has varied over time. Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class T Shares of the Fund commenced operations with the Fund's inception.

• The performance shown for Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class T Shares is calculated using the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class N Shares reflects the performance of the Fund's Class I Shares, calculated using the fees and expenses of Class N Shares, without the effect of any fee and expense limitations or waivers. If Class N Shares of the Fund had been available during the periods shown, the performance may have been different.

The bar chart depicts the Fund's performance during the period indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund's average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund's performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund's performance has varied over time.

The bar chart depicts the Fund's performance during the period indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund's average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-877-335-2687

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/advisor/mutual-funds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class I Shares (calendar year-end)

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Second Quarter 2011  2.77%          Worst Quarter:  Third Quarter 2011  0.72%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund's year-to-date return as of the calendar quarter ended September 30, 2012 was 7.94%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Janus Global Bond Fund | Class A, C, S, I, N, T Shares | Class A

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class A

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

4.75%

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class A

Management Fees

rr_ManagementFeesOverAssets

0.60%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.60%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.45%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.44%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.01%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleYear01

616

3 Years

rr_ExpenseExampleYear03

912

5 Years

rr_ExpenseExampleYear05

1,230

10 Years

rr_ExpenseExampleYear10

2,128

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

616

3 Years

rr_ExpenseExampleNoRedemptionYear03

912

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,230

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,128

Janus Global Bond Fund | Class A, C, S, I, N, T Shares | Class C

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class C

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

1.00%

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class C

Management Fees

rr_ManagementFeesOverAssets

0.60%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

0.61%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

2.21%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.45%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.76%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleYear01

324

3 Years

rr_ExpenseExampleYear03

691

5 Years

rr_ExpenseExampleYear05

1,185

10 Years

rr_ExpenseExampleYear10

2,544

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

224

3 Years

rr_ExpenseExampleNoRedemptionYear03

691

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,185

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,544

Janus Global Bond Fund | Class A, C, S, I, N, T Shares | Class S

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class S

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class S

Management Fees

rr_ManagementFeesOverAssets

0.60%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.77%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.62%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.36%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.26%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleYear01

165

3 Years

rr_ExpenseExampleYear03

511

5 Years

rr_ExpenseExampleYear05

881

10 Years

rr_ExpenseExampleYear10

1,922

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

165

3 Years

rr_ExpenseExampleNoRedemptionYear03

511

5 Years

rr_ExpenseExampleNoRedemptionYear05

881

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,922

Janus Global Bond Fund | Class A, C, S, I, N, T Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class I

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class I

Management Fees

rr_ManagementFeesOverAssets

0.60%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.53%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.13%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.37%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.76%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleYear01

115

3 Years

rr_ExpenseExampleYear03

359

5 Years

rr_ExpenseExampleYear05

622

10 Years

rr_ExpenseExampleYear10

1,375

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

115

3 Years

rr_ExpenseExampleNoRedemptionYear03

359

5 Years

rr_ExpenseExampleNoRedemptionYear05

622

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,375

2011

rr_AnnualReturn2011

6.67%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

7.94%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2011

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

2.77%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

0.72%

Janus Global Bond Fund | Class A, C, S, I, N, T Shares | Class N

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class N

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class N

Management Fees

rr_ManagementFeesOverAssets

0.60%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.53%

^[2]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.13%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.37%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.76%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class N Shares

1 Year

rr_ExpenseExampleYear01

115

3 Years

rr_ExpenseExampleYear03

359

5 Years

rr_ExpenseExampleYear05

622

10 Years

rr_ExpenseExampleYear10

1,375

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class N Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

115

3 Years

rr_ExpenseExampleNoRedemptionYear03

359

5 Years

rr_ExpenseExampleNoRedemptionYear05

622

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,375

Janus Global Bond Fund | Class A, C, S, I, N, T Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class T

Management Fees

rr_ManagementFeesOverAssets

0.60%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.78%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.38%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.37%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.01%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleYear01

140

3 Years

rr_ExpenseExampleYear03

437

5 Years

rr_ExpenseExampleYear05

755

10 Years

rr_ExpenseExampleYear10

1,657

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

140

3 Years

rr_ExpenseExampleNoRedemptionYear03

437

5 Years

rr_ExpenseExampleNoRedemptionYear05

755

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,657

Janus Global Bond Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class A

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class A Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[3]

1 Year

rr_AverageAnnualReturnYear01

1.44%

Since Inception

rr_AverageAnnualReturnSinceInception

1.42%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 28, 2010

Janus Global Bond Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class C

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class C Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[4]

1 Year

rr_AverageAnnualReturnYear01

4.78%

Since Inception

rr_AverageAnnualReturnSinceInception

5.76%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 28, 2010

Janus Global Bond Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class S

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class S Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

6.34%

Since Inception

rr_AverageAnnualReturnSinceInception

6.29%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 28, 2010

Janus Global Bond Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

6.67%

Since Inception

rr_AverageAnnualReturnSinceInception

6.62%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 28, 2010

Janus Global Bond Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class N

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class N Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

6.27%

Since Inception

rr_AverageAnnualReturnSinceInception

6.21%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 28, 2010

Janus Global Bond Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

6.51%

Since Inception

rr_AverageAnnualReturnSinceInception

6.45%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 28, 2010

Janus Global Bond Fund | Class A, C, S, I, N, T Shares | Return After Taxes on Distributions | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

5.29%

Since Inception

rr_AverageAnnualReturnSinceInception

5.24%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 28, 2010

Janus Global Bond Fund | Class A, C, S, I, N, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

1 Year

rr_AverageAnnualReturnYear01

4.34%

Since Inception

rr_AverageAnnualReturnSinceInception

4.84%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 28, 2010

Janus Global Bond Fund | Class A, C, S, I, N, T Shares | Barclays Global Aggregate Bond Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Barclays Global Aggregate Bond Index

1 Year

rr_AverageAnnualReturnYear01

5.64%

Since Inception

rr_AverageAnnualReturnSinceInception

7.16%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 28, 2010

Janus Global Bond Fund | Class A, C, S, I, N, T Shares | Barclays Global Aggregate Corporate Bond Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Barclays Global Aggregate Corporate Bond Index

1 Year

rr_AverageAnnualReturnYear01

4.32%

Since Inception

rr_AverageAnnualReturnSinceInception

6.05%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 28, 2010

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, and Class S Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 0.75% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees. For a period of three years subsequent to the Fund's commencement of operations (December 28, 2010) or until the Fund's assets exceed the first breakpoint in the investment advisory fee schedule, whichever occurs first, Janus Capital may recover from the Fund fees and expenses previously waived or reimbursed, which could then be considered a deferral, if the Fund's expense ratio, including recovered expenses, falls below the expense limit.

[2] Other Expenses for Class N Shares are based on the estimated expenses that the Shares expect to incur during their initial fiscal period.

[3] Calculated assuming maximum permitted sales loads.

[4] The one year return is calculated to include the contingent deferred sales charge.

XML

Perkins Mid Cap Value Fund | Class D Shares

Fund summary

Perkins Mid Cap Value Fund

INVESTMENT OBJECTIVE

Perkins Mid Cap Value Fund seeks capital appreciation.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses	Perkins Mid Cap Value Fund Class D Shares Class D
Operating Expenses Column [Text]	Class D
Management Fees (may adjust up or down)	0.54%
Other Expenses	0.20%
Total Annual Fund Operating Expenses	0.74%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Perkins Mid Cap Value Fund Class D Shares Class D	Class D Shares	76	237	411	918

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 54% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objective by investing primarily in common stocks selected for their capital appreciation potential. The Fund primarily invests in the common stocks of mid-sized companies whose stock prices the portfolio managers believe to be undervalued. The Fund invests, under normal circumstances, at least 80% of its net assets in equity securities of companies whose market capitalization falls, at the time of purchase, within the 12-month average of the capitalization range of the Russell Midcap^® Value Index. This average is updated monthly. The market capitalizations within the index will vary, but as of June 30, 2012, they ranged from approximately $1.3 billion to $18.5 billion. The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets. The Fund may invest, under normal circumstances, up to 20% of its net assets in securities of companies having market capitalizations outside of the aforementioned market capitalization ranges. In addition, when the portfolio managers believe that market conditions are unfavorable for investing, or when they are otherwise unable to locate attractive investment opportunities, the Fund may invest up to 20% of its net assets in cash or similar investments.

The Fund focuses on companies that have fallen out of favor with the market or that appear to be temporarily misunderstood by the investment community. The Fund’s portfolio managers generally look for companies with:

•  strong balance sheets and solid recurring free cash flows
•  attractive relative and absolute valuation ratios or that have underperformed recently
•  favorable reward to risk characteristics

The Fund may also invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. The Fund has and is expected to continue to buy and sell put and call options, particularly on market indices, for hedging purposes (to offset risks associated with an investment, currency exposure, or market conditions) and to enhance returns. The Fund’s exposure to derivatives will vary, is not limited to those derivatives listed, and could be significant at times. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s portfolio managers. When the Fund’s investments in cash or similar investments increase due to a lack of favorable investment opportunities or other extraordinary factors, the Fund may not participate in market advances or declines to the same extent that it would if the Fund had been fully invested.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Mid-Sized Companies Risk. The Fund’s investments in securities issued by mid-sized companies may involve greater risks than are customarily associated with larger, more established companies. Securities issued by mid-sized companies tend to be more volatile than securities issued by larger or more established companies and may underperform as compared to the securities of larger companies.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares (formerly named Investor Shares). For the periods prior to April 21, 2003, the performance shown for Class D Shares reflects the historical performance of Berger Mid Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Mid Cap Value Fund – Investor Shares into the Fund’s Class J Shares). If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Annual Total Returns for Class D Shares (calendar year-end)

Best Quarter:  Second Quarter 2003  17.17%          Worst Quarter:  Fourth Quarter 2008  −19.63%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 9.11%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Perkins Mid Cap Value Fund Class D Shares	Column	Label		1 Year	5 Years	10 Years	Since Inception of Predecessor Fund	Inception Date
Class D Return Before Taxes	Class D Shares	Return Before Taxes		(2.42%)	2.68%	7.60%	11.78%	Aug. 12, 1998
Class D Return After Taxes on Distributions	Class D Shares	Return After Taxes on Distributions		(3.77%)	1.67%	6.50%	10.32%	Aug. 12, 1998
Class D Return After Taxes on Distributions and Sale of Fund Shares	Class D Shares	Return After Taxes on Distributions and Sale of Fund Shares	[1]	(0.08%)	2.08%	6.36%	9.96%	Aug. 12, 1998
Russell Midcap Value Index (reflects no deduction for expenses, fees, or taxes)		Russell Midcap® Value Index		(1.38%)	0.04%	7.67%	7.70%	Aug. 12, 1998

After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; for the Fund’s Class J Shares (formerly named Investor Shares) for the period April 21, 2003 to February 16, 2010; and for Berger Mid Cap Value Fund – Investor Shares for periods prior to April 21, 2003. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

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Value

Risk/Return:

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Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

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Oct. 26, 2012

Perkins Value Plus Income Fund | Class D Shares

Risk/Return:

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Risk/Return [Heading]

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Fund summary

Perkins Value Plus Income Fund

Objective [Heading]

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INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

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Perkins Value Plus Income Fund seeks capital appreciation and current income.

Expense [Heading]

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FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

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This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

Operating Expenses Caption [Text]

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ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

November 1, 2013

Portfolio Turnover [Heading]

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Portfolio Turnover:

Portfolio Turnover [Text Block]

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The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 100% of the average value of its portfolio.

Portfolio Turnover, Rate

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100.00%

Expense Example [Heading]

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EXAMPLE:

Expense Example by Year [Heading]

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The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers or recoupments (if applicable) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

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The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Strategy [Heading]

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PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

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The Fund pursues its investment objective by normally investing 40-60% of its assets in equity securities selected primarily for capital appreciation and investing the remainder in fixed-income securities and cash equivalents.

Equity Securities. The Fund’s equity investments generate total return from a combination of capital appreciation and, to a lesser degree, current income. Such equity investments may include companies of any size, but the Fund will invest primarily in large- and mid-sized companies whose stock prices the portfolio managers believe to be undervalued or have the potential for high relative dividend yields, or both. The Fund’s equity portfolio managers invest in companies which have fallen out of favor with the market or that appear to be temporarily misunderstood by the investment community. The Fund’s equity portfolio managers generally look for companies with:

• strong balance sheets and solid recurring free cash flows
• attractive relative and absolute valuation ratios or that have underperformed recently
• favorable reward to risk characteristics

Fixed-Income Securities. The Fund’s fixed-income investments generate total return from a combination of current income and capital appreciation, but income is usually the dominant portion. The Fund normally invests the portion of its assets allocated to fixed-income investments in debt securities (including, but not limited to, government bonds, corporate bonds, mortgage-backed securities, asset-backed securities, zero-coupon bonds, and bank loans), convertible securities, and short-term securities. The Fund invests at least 50% of the fixed-income portion of its assets in investment grade debt securities. The Fund will limit its investment in high-yield/high-risk bonds, also known as “junk” bonds, to 50% or less of the fixed-income portion of its net assets.

In addition to considering economic factors such as the effect of interest rates on the Fund’s fixed-income investments, the Fund’s fixed-income portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income-producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets.

The Fund may also invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. The Fund has and is expected to continue to buy and sell put and call options to enhance returns. The Fund’s exposure to derivatives will vary, is not limited to those derivatives listed, and could be significant at times. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

Janus Capital is primarily responsible for the overall asset allocation of the Fund and manages the Fund’s fixed-income investments. Cash positions are considered a part of the Fund’s fixed-income allocation and will be managed by the Fund’s fixed-income portfolio managers. Perkins manages the Fund’s equity investments and assists the adviser in determining the Fund’s overall asset allocation. The Fund may periodically adjust its mix of equity and fixed-income investments in response to changing economic and market conditions, including outside the range of 40-60% of its assets in equity securities. Due to the nature of the fixed-income securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

Risk [Heading]

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PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

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The biggest risk is that the Fund’s returns and yields will vary, and you could lose money. The Fund is designed for long-term investors seeking a portfolio including common stocks and bonds selected for their potential to produce capital appreciation and current income. Common stocks tend to be more volatile than many other investment choices.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s equity portfolio managers.

Mid-Sized Companies Risk. The Fund’s investments in securities issued by mid-sized companies may involve greater risks than are customarily associated with larger, more established companies. Securities issued by mid-sized companies tend to be more volatile than securities issued by larger or more established companies and may underperform as compared to the securities of larger companies.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

High-Yield/High-Risk Bond Risk. High-yield/high-risk bonds may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Bank Loan Risk. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. Participation interests and assignments involve credit, interest rate, and liquidity risk. In addition, the bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

Foreign Exposure Risk. The Fund may have significant exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited.

Allocation Risk. The Fund’s ability to achieve its investment objective depends largely upon the allocation of assets among the equity and fixed asset categories. You could lose money on your investment in the Fund as a result of these allocations. Portfolio management may favor an asset category that underperforms relative to other asset categories. For example, the Fund may be overweighted in equity securities when the stock market is falling and the fixed-income market is rising. Additionally, periodic rebalancing of Fund assets among asset categories may result in increased transaction costs, which may have a negative effect on the Fund’s performance.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

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The biggest risk is that the Fund’s returns and yields will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

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PERFORMANCE INFORMATION

Performance Narrative [Text Block]

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The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. The bar chart depicts the Fund’s performance during the period indicated. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the Fund’s performance during the period indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-800-525-3713

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/allfunds

Performance Past Does Not Indicate Future [Text]

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The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

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Annual Total Returns for Class D Shares (calendar year-end)

Bar Chart Closing [Text Block]

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Best Quarter:  Fourth Quarter 2011  7.30%        Worst Quarter:  Third Quarter 2011  −7.84%

Year to Date Return, Label

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The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 10.38%.

Performance Table Heading

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Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

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The Value Income Index is an internally-calculated, hypothetical combination of unmanaged indices that combines total returns from the Russell 1000^® Value Index (50%) and the Barclays U.S. Aggregate Bond Index (50%).

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Closing [Text Block]

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Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Perkins Value Plus Income Fund | Class D Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class D

Management Fees

rr_ManagementFeesOverAssets

0.60%

Other Expenses

rr_OtherExpensesOverAssets

0.81%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.41%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.50%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.91%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class D Shares

1 Year

rr_ExpenseExampleYear01

144

3 Years

rr_ExpenseExampleYear03

446

5 Years

rr_ExpenseExampleYear05

771

10 Years

rr_ExpenseExampleYear10

1,691

2011

rr_AnnualReturn2011

3.66%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

10.38%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Dec. 31, 2011

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

7.30%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(7.84%)

Perkins Value Plus Income Fund | Class D Shares | Return Before Taxes | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

3.66%

Since Inception

rr_AverageAnnualReturnSinceInception

9.21%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 30, 2010

Perkins Value Plus Income Fund | Class D Shares | Return After Taxes on Distributions | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

1.61%

Since Inception

rr_AverageAnnualReturnSinceInception

7.38%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 30, 2010

Perkins Value Plus Income Fund | Class D Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[2]

1 Year

rr_AverageAnnualReturnYear01

2.68%

Since Inception

rr_AverageAnnualReturnSinceInception

6.92%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 30, 2010

Perkins Value Plus Income Fund | Class D Shares | Russell 1000 Value Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Russell 1000^® Value Index

1 Year

rr_AverageAnnualReturnYear01

0.39%

Since Inception

rr_AverageAnnualReturnSinceInception

9.97%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 30, 2010

Perkins Value Plus Income Fund | Class D Shares | Barclays U.S. Aggregate Bond Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Barclays U.S. Aggregate Bond Index

1 Year

rr_AverageAnnualReturnYear01

7.84%

Since Inception

rr_AverageAnnualReturnSinceInception

5.51%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 30, 2010

Perkins Value Plus Income Fund | Class D Shares | Value Income Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Value Income Index

1 Year

rr_AverageAnnualReturnYear01

4.44%

Since Inception

rr_AverageAnnualReturnSinceInception

8.16%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 30, 2010

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding administrative services fees payable pursuant to the Transfer Agency Agreement, brokerage commissions, interest, dividends, taxes, acquired fund fees and expenses, and extraordinary expenses) to 0.76% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees. For a period of three years subsequent to the Fund's commencement of operations (July 30, 2010), Janus Capital may recover from the Fund fees and expenses previously waived or reimbursed, which could then be considered a deferral, if the Fund's expense ratio, including recovered expenses, falls below the expense limit.

[2] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Label

Element

Value

Risk/Return:

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Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Janus Conservative Allocation Fund | Class A, C, S, I, T Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

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Fund summary

Janus Conservative Allocation Fund

Objective [Heading]

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INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

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Janus Conservative Allocation Fund seeks total return through a primary emphasis on income with a secondary emphasis on growth of capital.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

SHAREHOLDER FEES
(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 10% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

10.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 45 of the Fund’s Prospectus and in the “Purchases” section on page 63 of the Fund’s Statement of Additional Information.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses (including the operating expenses of the underlying funds) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

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The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Expense Example by, Year, Caption [Text]

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If Shares are redeemed:

Expense Example, No Redemption, By Year, Caption [Text]

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If Shares are not redeemed:

Strategy [Heading]

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PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

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The Fund seeks to achieve its investment objective by investing in other Janus mutual funds (“underlying funds”) that represent a variety of asset classes and investment styles. The Fund pursues this objective by investing in a diversified portfolio of underlying funds resulting in an allocation of the Fund’s investments that normally provides exposure of approximately 40% to stocks and 60% to bonds and money market securities. The target allocation and the allocation of the Fund’s assets among underlying funds are based on quantitative and qualitative analysis. Because it invests in other funds, the Fund is considered a “fund of funds.”

The Fund’s asset allocation is intended to diversify investments among stocks, bonds, and cash equivalents. The portfolio manager regularly reviews the allocation of Fund assets in the underlying funds and may modify the underlying funds’ weightings or substitute other underlying funds to emphasize and mitigate risk exposures that may arise as a result of the implementation of the allocations. An independent asset allocation service provides evaluations of asset allocations that the portfolio manager may use in implementing the allocations among the underlying funds. The portfolio manager continually monitors asset class allocations and periodically rebalances the Fund’s investments in the underlying funds. The portfolio manager may change the Fund’s asset class allocations, the underlying funds, an underlying fund’s asset category, or weightings among asset classes or underlying funds without prior shareholder notice.

The Fund will normally allocate approximately 60% of its investments to underlying bond funds and money market instruments; and approximately 40% of its investments to underlying funds that provide varying exposure to common stocks of large U.S.-based companies, small- to mid-capitalization companies, and international companies (including those with exposure to emerging markets). Refer to Appendix A in this Prospectus for a brief description of the investment strategies of each of the currently available underlying funds.

When market conditions dictate a more defensive strategy, the Fund or an underlying fund may temporarily hold cash or invest its assets in temporary investments. In that case, the Fund may take positions that are inconsistent with its investment objective. As a result, the Fund may not achieve its investment objective.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking income and, to a lesser extent, growth of capital. Investments in a portfolio with common stock exposure tend to be more volatile than many other investment choices.

Main Risks Associated with the Fund
Allocation Risk. The Fund’s ability to achieve its investment objective depends largely upon the portfolio manager’s allocation of assets among the underlying funds and other securities, using the optimization process (a process that utilizes quantitative analysis of a number of factors, such as historical risk, performance, fund classifications, and the relationship among underlying funds) and the judgment of the portfolio manager. You could lose money on your investment in the Fund as a result of these allocations. The Fund will typically invest in a number of different underlying funds; however, to the extent that the Fund invests a significant portion of its assets in a single underlying fund, it will be more sensitive to the risks associated with that fund and any investments in which that fund concentrates.

Affiliated Fund Risk. Janus Capital has the authority to select and substitute underlying affiliated mutual funds. The fees paid to Janus Capital by some Janus mutual funds are generally higher than the fees paid to Janus Capital by the Fund or by other funds and share classes available for investment by the Fund. These conditions may create a conflict of interest when selecting underlying affiliated mutual funds and share classes for investment. Janus Capital, however, is a fiduciary to the Fund and its shareholders and is legally obligated to act in their best interest when selecting underlying affiliated mutual funds.

Main Risks Associated with the Underlying Funds and Securities
The biggest risk is that the underlying funds’ returns will vary, and you could lose money.

Fixed-Income Securities Risk. Approximately 60% of the Fund’s assets are allocated to fixed-income securities through investments in underlying funds. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause an underlying fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which an underlying fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that an underlying fund’s portfolio manager would like or at the price that the portfolio manager believes the security is currently worth.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Market Risk. Approximately 40% of the Fund’s assets are allocated to equity investments through investments in underlying funds. The value of an underlying fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if a portfolio manager’s belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of an underlying fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Foreign Exposure Risk. Certain underlying funds may have significant exposure to foreign markets as a result of their investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, an underlying fund’s returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. A market swing in one or more countries or regions where an underlying fund has invested a significant amount of its assets may have a greater effect on an underlying fund’s performance than it would in a more geographically diversified portfolio. An underlying fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Emerging Markets Risk. The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities involve a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. In addition, an underlying fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of an underlying fund’s investments. To the extent that an underlying fund invests a significant portion of its assets in the securities of issuers in or companies of a single country or region, it is more likely to be impacted by events or conditions affecting that country or region, which could have a negative impact on the Fund’s performance. Some of the risks of investing directly in foreign and emerging market securities may be reduced when an underlying fund invests indirectly in foreign securities through various other investment vehicles including derivatives, which also involve other risks.

Sovereign Debt Risk. An underlying fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

Exchange-Traded Funds Risk. Certain underlying funds may purchase shares of exchange-traded funds (“ETFs”) to gain exposure to a particular portion of the market. ETFs are pooled investment vehicles, which may be managed or unmanaged, that generally seek to track the performance of a specific index. ETFs are traded on an exchange at market prices that may vary from the net asset value of their underlying investments. When an underlying fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF’s expenses. ETFs have certain inherent risks generally associated with investments in a portfolio of securities in which the ETF is invested, including the risk that the general level of stock prices may decline, thereby adversely affecting the value of each unit of the ETF. ETFs also involve the risk that an active trading market for an ETF’s shares may not develop or be maintained.

Exchange-Traded Notes Risk. Certain underlying funds may invest in exchange-traded notes (“ETNs”), which are debt securities whose returns are linked to a particular index. ETNs are typically linked to the performance of a commodities index that reflects the potential return on unleveraged investments in futures contracts of physical commodities, plus a specified rate of interest that could be earned on cash collateral. ETNs are subject to credit risk. The value of an ETN may vary and may be influenced by time to maturity, level of supply and demand for the ETN, volatility and lack of liquidity in underlying commodities markets, changes in the applicable interest rates, changes in the issuer’s credit rating, and economic, legal, political, or geographic events that affect the referenced commodity. When an underlying fund invests in ETNs it will bear its proportionate share of any fees and expenses borne by the ETN. There may be restrictions on an underlying fund’s right to redeem its investment in an ETN, which is meant to be held until maturity. An underlying fund’s decision to sell its ETN holdings may be limited by the availability of a secondary market.

Derivatives Risk. Certain underlying funds may invest in derivatives. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

The biggest risk is that the Fund’s returns will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares, the initial share class) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund commenced operations on July 6, 2009.

• The performance shown for Class T Shares is calculated using the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class A Shares, Class C Shares, Class S Shares, and Class I Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers.

If Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund had been available during periods prior to July 6, 2009, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, and Class I Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. Performance information for each underlying fund is available in its prospectus and/or the most recent annual or semiannual report. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-877-335-2687

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/advisor/mutual-funds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class T Shares (calendar year-end)

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Second Quarter 2009  10.64%          Worst Quarter:  Third Quarter 2008   −6.58%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 9.25%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The Conservative Allocation Index is an internally-calculated, hypothetical combination of unmanaged indices that combines total returns from the Barclays U.S. Aggregate Bond Index (60%), the Dow Jones Wilshire 5000 Index (28%), and the Morgan Stanley Capital International Europe, Australasia, Far East Index (“MSCI EAFE^®”) Index (12%).

After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares, the initial share class). After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Class A

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class A

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class A

Management Fees

rr_ManagementFeesOverAssets

0.05%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.18%

^[1]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.64%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.11%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleYear01

682

3 Years

rr_ExpenseExampleYear03

908

5 Years

rr_ExpenseExampleYear05

1,151

10 Years

rr_ExpenseExampleYear10

1,849

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

682

3 Years

rr_ExpenseExampleNoRedemptionYear03

908

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,151

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,849

Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Class C

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class C

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

1.00%

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class C

Management Fees

rr_ManagementFeesOverAssets

0.05%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

0.20%

^[1]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.64%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.89%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleYear01

292

3 Years

rr_ExpenseExampleYear03

594

5 Years

rr_ExpenseExampleYear05

1,021

10 Years

rr_ExpenseExampleYear10

2,212

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

192

3 Years

rr_ExpenseExampleNoRedemptionYear03

594

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,021

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,212

Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Class S

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class S

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class S

Management Fees

rr_ManagementFeesOverAssets

0.05%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.33%

^[1]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.64%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.27%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleYear01

129

3 Years

rr_ExpenseExampleYear03

403

5 Years

rr_ExpenseExampleYear05

697

10 Years

rr_ExpenseExampleYear10

1,534

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

129

3 Years

rr_ExpenseExampleNoRedemptionYear03

403

5 Years

rr_ExpenseExampleNoRedemptionYear05

697

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,534

Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class I

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class I

Management Fees

rr_ManagementFeesOverAssets

0.05%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.18%

^[1]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.64%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.87%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleYear01

89

3 Years

rr_ExpenseExampleYear03

278

5 Years

rr_ExpenseExampleYear05

482

10 Years

rr_ExpenseExampleYear10

1,073

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

89

3 Years

rr_ExpenseExampleNoRedemptionYear03

278

5 Years

rr_ExpenseExampleNoRedemptionYear05

482

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,073

Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class T

Management Fees

rr_ManagementFeesOverAssets

0.05%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.33%

^[1]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.64%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.02%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleYear01

104

3 Years

rr_ExpenseExampleYear03

325

5 Years

rr_ExpenseExampleYear05

563

10 Years

rr_ExpenseExampleYear10

1,248

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

104

3 Years

rr_ExpenseExampleNoRedemptionYear03

325

5 Years

rr_ExpenseExampleNoRedemptionYear05

563

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,248

2006

rr_AnnualReturn2006

11.09%

2007

rr_AnnualReturn2007

10.19%

2008

rr_AnnualReturn2008

(16.01%)

2009

rr_AnnualReturn2009

23.37%

2010

rr_AnnualReturn2010

10.60%

2011

rr_AnnualReturn2011

1.39%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

9.25%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

10.64%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(6.58%)

Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class A

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class A Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[2]

1 Year

rr_AverageAnnualReturnYear01

(4.40%)

5 Years

rr_AverageAnnualReturnYear05

3.68%

Since Inception

rr_AverageAnnualReturnSinceInception

4.83%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class C

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class C Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[3]

1 Year

rr_AverageAnnualReturnYear01

(0.28%)

5 Years

rr_AverageAnnualReturnYear05

4.15%

Since Inception

rr_AverageAnnualReturnSinceInception

5.10%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class S

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class S Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

1.13%

5 Years

rr_AverageAnnualReturnYear05

4.63%

Since Inception

rr_AverageAnnualReturnSinceInception

5.59%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

1.59%

5 Years

rr_AverageAnnualReturnYear05

5.07%

Since Inception

rr_AverageAnnualReturnSinceInception

6.04%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

1.39%

5 Years

rr_AverageAnnualReturnYear05

5.07%

Since Inception

rr_AverageAnnualReturnSinceInception

6.04%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Return After Taxes on Distributions | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

0.44%

5 Years

rr_AverageAnnualReturnYear05

3.96%

Since Inception

rr_AverageAnnualReturnSinceInception

5.00%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[4]

1 Year

rr_AverageAnnualReturnYear01

0.99%

5 Years

rr_AverageAnnualReturnYear05

3.73%

Since Inception

rr_AverageAnnualReturnSinceInception

4.63%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | S&P 500 Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

S&P 500^® Index

1 Year

rr_AverageAnnualReturnYear01

2.11%

5 Years

rr_AverageAnnualReturnYear05

(0.25%)

Since Inception

rr_AverageAnnualReturnSinceInception

2.26%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Conservative Allocation Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Conservative Allocation Index

1 Year

rr_AverageAnnualReturnYear01

3.61%

5 Years

rr_AverageAnnualReturnYear05

3.89%

Since Inception

rr_AverageAnnualReturnSinceInception

4.89%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

[1] Other Expenses are based on the estimated expenses that the Fund expects to incur.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

[4] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

INTECH Global Dividend Fund | Class D Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

INTECH Global Dividend Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

INTECH Global Dividend Fund seeks long-term growth of capital and income.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
    (expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

November 1, 2013

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the period December 15, 2011 to June 30, 2012, the Fund’s portfolio turnover rate was 24% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

24.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers or recoupments (if applicable) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund invests, under normal circumstances, at least 80% of its net assets in dividend-paying securities. The Fund invests primarily in common stocks from the universe of the Morgan Stanley Capital International (“MSCI”) World High Dividend Yield Index, utilizing INTECH’s mathematical investment process. The MSCI World High Dividend Yield Index is designed to reflect the performance of the high dividend yield securities contained within the broader MSCI World Index^sm. The Fund may also invest in foreign equity and debt securities.

The Fund pursues its investment objective by applying a mathematical investment process to construct an investment portfolio from the universe of common stocks within its named benchmark index. The goal of this process is to build a portfolio of stocks in a more efficient combination than the named benchmark index. The process seeks to capitalize on the natural volatility of the market by searching for stocks within the index that have high relative volatility (providing the potential for excess returns) but that essentially move in opposite directions or have low correlation to each other (providing the potential for lower relative risk). By constructing the portfolio in this manner and periodically rebalancing the portfolio to maintain potentially more efficient weightings, INTECH’s mathematical investment process seeks to create a portfolio that, over time, produces returns in excess of its named benchmark index with risks similar to that of the benchmark index. The rebalancing techniques used by INTECH may result in a higher portfolio turnover compared to a “buy and hold” fund strategy.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Foreign Exposure Risk. The Fund normally has significant exposure to foreign markets as a result of its investments in foreign securities, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio.

Dividend Risk. Companies that issue dividend-yielding securities are not required to continue to pay dividends on such securities. Therefore, there is the possibility that such companies could reduce or eliminate the payment of dividends in the future.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Investment Process Risk. The proprietary mathematical investment process used by INTECH may not achieve the desired results. On an occasional basis, INTECH considers changes to its mathematical investment process. These changes may result in changes to the portfolio, might not provide the intended results, and may adversely impact the Fund’s performance.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

The biggest risk is that the Fund’s returns will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The Fund does not have a full calendar year of operations. Performance information for certain periods is included in the Fund’s first annual and/or semiannual report.

Performance One Year or Less [Text]

rr_PerformanceOneYearOrLess

The Fund does not have a full calendar year of operations.

INTECH Global Dividend Fund | Class D Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class D

Management Fees

rr_ManagementFeesOverAssets

0.55%

Other Expenses

rr_OtherExpensesOverAssets

5.60%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

6.15%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

5.34%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.81%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class D Shares

1 Year

rr_ExpenseExampleYear01

611

3 Years

rr_ExpenseExampleYear03

1,813

5 Years

rr_ExpenseExampleYear05

2,988

10 Years

rr_ExpenseExampleYear10

5,808

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding administrative services fees payable pursuant to the Transfer Agency Agreement, brokerage commissions, interest, dividends, taxes, acquired fund fees and expenses, and extraordinary expenses) to 0.50% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees. For a period of three years subsequent to the Fund's commencement of operations (December 15, 2011), Janus Capital may recover from the Fund fees and expenses previously waived or reimbursed, which could then be considered a deferral, if the Fund's expense ratio, including recovered expenses, falls below the expense limit.

XML

INTECH U.S. Value Fund | Class A, C, S, I, T Shares

Fund summary

INTECH U.S. Value Fund

INVESTMENT OBJECTIVE

INTECH U.S. Value Fund seeks long-term growth of capital.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 46 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.

SHAREHOLDER FEES
(fees paid directly from your investment)

Shareholder Fees INTECH U.S. Value Fund Class A, C, S, I, T Shares	Class A	Class C	Class S	Class I	Class T
Shareholder Fees Column [Text]	Class A	Class C	Class S	Class I	Class T
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	5.75%	none	none	none	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	none	1.00%	none	none	none

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses INTECH U.S. Value Fund Class A, C, S, I, T Shares		Class A	Class C	Class S	Class I	Class T
Operating Expenses Column [Text]		Class A	Class C	Class S	Class I	Class T
Management Fees		0.50%	0.50%	0.50%	0.50%	0.50%
Distribution/Service (12b-1) Fees		0.25%	1.00%	0.25%	none	none
Other Expenses		0.17%	0.36%	0.40%	0.17%	0.39%
Total Annual Fund Operating Expenses	[1]	0.92%	1.86%	1.15%	0.67%	0.89%
Fee Waiver	[1]	none	0.11%	none	none	none
Total Annual Fund Operating Expenses After Fee Waiver	[1]	0.92%	1.75%	1.15%	0.67%	0.89%

EXAMPLE:

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

If Shares are redeemed:

Expense Example INTECH U.S. Value Fund Class A, C, S, I, T Shares (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	663	851	1,055	1,641
Class C	Class C Shares	289	585	1,006	2,180
Class S	Class S Shares	117	365	633	1,398
Class I	Class I Shares	68	214	373	835
Class T	Class T Shares	91	284	493	1,096

If Shares are not redeemed:

Expense Example, No Redemption INTECH U.S. Value Fund Class A, C, S, I, T Shares (USD $)	Expense Example, No Redemption, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	663	851	1,055	1,641
Class C	Class C Shares	189	585	1,006	2,180
Class S	Class S Shares	117	365	633	1,398
Class I	Class I Shares	68	214	373	835
Class T	Class T Shares	91	284	493	1,096

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 100% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund invests, under normal circumstances, at least 80% of its net assets in U.S. common stocks from the universe of the Russell 1000^® Value Index, utilizing INTECH’s mathematical investment process. The Russell 1000^® Value Index is an unmanaged index that measures the performance of those Russell 1000 companies with lower price-to-book ratios and lower forecasted growth values.

The Fund pursues its investment objective by applying a mathematical investment process to construct an investment portfolio from the universe of common stocks within its named benchmark index. The goal of this process is to build a portfolio of stocks in a more efficient combination than the named benchmark index. The process seeks to capitalize on the natural volatility of the market by searching for stocks within the index that have high relative volatility (providing the potential for excess returns) but that essentially move in opposite directions or have low correlation to each other (providing the potential for lower relative risk). By constructing the portfolio in this manner and periodically rebalancing the portfolio to maintain potentially more efficient weightings, INTECH’s mathematical investment process seeks to create a portfolio that, over time, produces returns in excess of its named benchmark index with risks similar to that of the benchmark index. The rebalancing techniques used by INTECH may result in a higher portfolio turnover compared to a “buy and hold” fund strategy.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Investment Process Risk. The proprietary mathematical investment process used by INTECH may not achieve the desired results. On an occasional basis, INTECH considers changes to its mathematical investment process. These changes may result in changes to the portfolio, might not provide the intended results, and may adversely impact the Fund’s performance.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class I Shares, Class A Shares, Class C Shares, and Class S Shares of the Fund commenced operations on July 6, 2009, after the reorganization of each corresponding class of shares of Janus Adviser INTECH Risk-Managed Value Fund (“JAD predecessor fund”) into each respective share class of the Fund. Class T Shares of the Fund commenced operations on July 6, 2009.

• The performance shown for Class I Shares, Class A Shares, Class C Shares, and Class S Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund’s Class I Shares, Class A Shares, Class C Shares, and Class S Shares prior to the reorganization, calculated using the fees and expenses of each respective share class of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class T Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund’s Class I Shares prior to the reorganization, calculated using the fees and expenses of Class T Shares, without the effect of any fee and expense limitations or waivers.

If Class T Shares of the Fund had been available during periods prior to July 6, 2009, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class I Shares, Class A Shares, Class C Shares, Class S Shares, and Class T Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Annual Total Returns for Class I Shares (calendar year-end)

Best Quarter:  Third Quarter 2009  17.79%     Worst Quarter:  Fourth Quarter 2008  −21.39%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 13.89%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns INTECH U.S. Value Fund Class A, C, S, I, T Shares

Column

Label

1 Year

5 Years

Since Inception of Predecessor Fund

Inception Date

Class I Shares Return Before Taxes

Class I Shares

Return Before Taxes

2.28%

(1.62%)

1.37%

Dec. 30, 2005

Class I Shares Return After Taxes on Distributions

Class I Shares

Return After Taxes on Distributions

2.02%

(2.01%)

0.96%

Dec. 30, 2005

Class I Shares Return After Taxes on Distributions and Sale of Fund Shares

Class I Shares

Return After Taxes on Distributions and Sale of Fund Shares

^[1]

1.83%

(1.46%)

1.07%

Dec. 30, 2005

Class A Shares Return Before Taxes

Class A Shares

Return Before Taxes

^[2]

(3.79%)

(3.00%)

0.14%

Dec. 30, 2005

Class C Shares Return Before Taxes

Class C Shares

Return Before Taxes

^[3]

0.16%

(2.58%)

0.37%

Dec. 30, 2005

Class S Shares Return Before Taxes

Class S Shares

Return Before Taxes

1.81%

(2.09%)

0.89%

Dec. 30, 2005

Class T Shares Return Before Taxes

Class T Shares

Return Before Taxes

2.07%

(1.98%)

0.96%

Dec. 30, 2005

Russell 1000 Value Index (reflects no deduction for expenses, fees, or taxes)

Russell 1000® Value Index

0.39%

(2.64%)

1.13%

Dec. 30, 2005

After-tax returns are calculated using distributions for the Fund’s Class I Shares for periods following July 6, 2009; and for the JAD predecessor fund’s Class I Shares for periods prior to July 6, 2009. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, and Class S Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 0.75% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

XML

Janus Money Market Fund | Class T Shares

Fund summary

Janus Money Market Fund

INVESTMENT OBJECTIVES

Janus Money Market Fund seeks capital preservation and liquidity

with current income as a secondary objective.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses	Janus Money Market Fund Class T Shares Class T
Operating Expenses Column [Text]	Class T
Management Fees	0.20%
Other Expenses	0.49%
Total Annual Fund Operating Expenses	0.69%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Janus Money Market Fund Class T Shares Class T	Class T Shares	70	221	384	859

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objectives by investing primarily in high quality debt obligations and obligations of financial institutions. Debt obligations may include commercial paper, notes and bonds, and variable amount master demand notes. Obligations of financial institutions include certificates of deposit and time deposits. The Fund also intends to invest in repurchase agreements including those secured by U.S. Government agencies. Some government agencies backed by the full faith and credit of the United States are supported by the issuer’s ability to borrow from the United States Treasury, some are supported only by the credit of the issuer, and some are supported by the United States in some other way.

The Fund will:

• invest in high quality, short-term money market instruments that present minimal credit risks, as determined by Janus Capital

• invest only in U.S. dollar-denominated instruments that have a remaining maturity of 397 days or less (as calculated pursuant to Rule 2a-7 under the Investment Company Act of 1940, as amended)

• maintain a dollar-weighted average portfolio maturity of 60 days or less and maintain a dollar-weighted average portfolio life (portfolio maturity measured without reference to any maturity shortening provisions of adjustable rate securities by reference to their interest rate reset dates) of 120 days or less

PRINCIPAL INVESTMENT RISKS

Market Risk. The Fund’s yield will vary as the short-term securities in its portfolio mature and the proceeds are reinvested in securities with different interest rates. For capital preservation and liquidity, the Fund may have a greater concentration in short-term securities including, but not limited to, investing up to all of its assets in overnight securities, which may result in a reduction of the Fund’s yield. Over time, the real value of the Fund’s yield may be eroded by inflation. Although the Fund invests only in high-quality, short-term money market instruments, there is a risk that the value of the securities it holds will fall as a result of changes in interest rates, an issuer’s actual or perceived creditworthiness, or an issuer’s ability to meet its obligations. The credit quality of the Fund’s holdings can change rapidly in certain market environments and any downgrade or default of a portfolio security could cause the Fund’s share price or yield to fall.

Collateral Risk. With respect to collateral received in repurchase transactions or other investments, the Fund may have significant exposure to financial services, mortgage markets, and government agencies not secured by the full faith and credit of the United States. Such exposure, depending on market conditions, could have a negative impact on the Fund, including minimizing the value of any collateral.

Money Market Risk. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares, the initial share class) of the Fund commenced operations with the Fund’s inception. The performance shown for Class T Shares is calculated using the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table shows how the Fund’s returns over different periods average out. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Annual Total Returns for Class T Shares (calendar year-end)

Best Quarter:  Fourth Quarter 2006  1.23%     Worst Quarter:  Third Quarter 2011  0.00%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 0.00%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns	Column	Label	1 Year	5 Years	10 Years	Since Inception	Inception Date
Janus Money Market Fund Class T Shares Class T Return Before Taxes	Class T Shares	Return Before Taxes	0.01%	1.39%	1.73%	3.08%	Feb. 14, 1995

The 7-day yield on December 31, 2011 was 0.01% for Janus Money Market Fund.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Janus Growth Allocation Fund | Class D Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Janus Growth Allocation Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Janus Growth Allocation Fund seeks total return through a primary emphasis on growth of capital with a secondary emphasis on income.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 18% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

18.00%

Expense Example [Heading]

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EXAMPLE:

Expense Example by Year [Heading]

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The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses (including the operating expenses of the underlying funds) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

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The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Strategy [Heading]

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PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

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The Fund seeks to achieve its investment objective by investing in other Janus mutual funds (“underlying funds”) that represent a variety of asset classes and investment styles. The Fund pursues this objective by investing in a diversified portfolio of underlying funds resulting in an allocation of the Fund’s investments that normally provides exposure of approximately 80% to stocks and 20% to bonds and money market securities. The target allocation and the allocation of the Fund’s assets among underlying funds are based on quantitative and qualitative analysis. Because it invests in other funds, the Fund is considered a “fund of funds.”

The Fund’s asset allocation is intended to diversify investments among stocks, bonds, and cash equivalents. The portfolio manager regularly reviews the allocation of Fund assets in the underlying funds and may modify the underlying funds’ weightings or substitute other underlying funds to emphasize and mitigate risk exposures that may arise as a result of the implementation of the allocations. An independent asset allocation service provides evaluations of asset allocations that the portfolio manager may use in implementing the allocations among the underlying funds. The portfolio manager continually monitors asset class allocations and periodically rebalances the Fund’s investments in the underlying funds. The portfolio manager may change the Fund’s asset class allocations, the underlying funds, an underlying fund’s asset category, or weightings among asset classes or underlying funds without prior shareholder notice.

The Fund will normally allocate approximately 80% of its investments to underlying funds that provide varying exposure to common stocks of large U.S.-based companies, small- to mid-capitalization companies, and international companies (including those with exposure to emerging markets); and approximately 20% of its investments to underlying bond funds and money market instruments. Refer to Appendix A in this Prospectus for a brief description of the investment strategies of each of the currently available underlying funds.

When market conditions dictate a more defensive strategy, the Fund or an underlying fund may temporarily hold cash or invest its assets in temporary investments. In that case, the Fund may take positions that are inconsistent with its investment objective. As a result, the Fund may not achieve its investment objective.

Risk [Heading]

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PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

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The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking growth of capital and, to a lesser extent, income. Investments in a portfolio with common stock exposure tend to be more volatile than many other investment choices.

Main Risks Associated with the Fund
Allocation Risk. The Fund’s ability to achieve its investment objective depends largely upon the portfolio manager’s allocation of assets among the underlying funds and other securities, using the optimization process (a process that utilizes quantitative analysis of a number of factors, such as historical risk, performance, fund classifications, and the relationship among underlying funds) and the judgment of the portfolio manager. You could lose money on your investment in the Fund as a result of these allocations. The Fund will typically invest in a number of different underlying funds; however, to the extent that the Fund invests a significant portion of its assets in a single underlying fund, it will be more sensitive to the risks associated with that fund and any investments in which that fund concentrates.

Affiliated Fund Risk. Janus Capital has the authority to select and substitute underlying affiliated mutual funds. The fees paid to Janus Capital by some Janus mutual funds are generally higher than the fees paid to Janus Capital by the Fund or by other funds and share classes available for investment by the Fund. These conditions may create a conflict of interest when selecting underlying affiliated mutual funds and share classes for investment. Janus Capital, however, is a fiduciary to the Fund and its shareholders and is legally obligated to act in their best interest when selecting underlying affiliated mutual funds.

Main Risks Associated with the Underlying Funds and Securities
The biggest risk is that the underlying funds’ returns will vary, and you could lose money.

Market Risk. Approximately 80% of the Fund’s assets are allocated to equity investments through investments in underlying funds. The value of an underlying fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if a portfolio manager’s belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of an underlying fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Fixed-Income Securities Risk. Approximately 20% of the Fund’s assets are allocated to fixed-income securities through investments in underlying funds. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause an underlying fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which an underlying fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that an underlying fund’s portfolio manager would like or at the price that the portfolio manager believes the security is currently worth.

Foreign Exposure Risk. Certain underlying funds may have significant exposure to foreign markets as a result of their investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, an underlying fund’s returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. A market swing in one or more countries or regions where an underlying fund has invested a significant amount of its assets may have a greater effect on an underlying fund’s performance than it would in a more geographically diversified portfolio. An underlying fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Emerging Markets Risk. The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities involve a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. In addition, an underlying fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of an underlying fund’s investments. To the extent that an underlying fund invests a significant portion of its assets in the securities of issuers in or companies of a single country or region, it is more likely to be impacted by events or conditions affecting that country or region, which could have a negative impact on the Fund’s performance. Some of the risks of investing directly in foreign and emerging market securities may be reduced when an underlying fund invests indirectly in foreign securities through various other investment vehicles including derivatives, which also involve other risks.

Sovereign Debt Risk. An underlying fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Exchange-Traded Funds Risk. Certain underlying funds may purchase shares of exchange-traded funds (“ETFs”) to gain exposure to a particular portion of the market. ETFs are pooled investment vehicles, which may be managed or unmanaged, that generally seek to track the performance of a specific index. ETFs are traded on an exchange at market prices that may vary from the net asset value of their underlying investments. When an underlying fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF’s expenses. ETFs have certain inherent risks generally associated with investments in a portfolio of securities in which the ETF is invested, including the risk that the general level of stock prices may decline, thereby adversely affecting the value of each unit of the ETF. ETFs also involve the risk that an active trading market for an ETF’s shares may not develop or be maintained.

Exchange-Traded Notes Risk. Certain underlying funds may invest in exchange-traded notes (“ETNs”), which are debt securities whose returns are linked to a particular index. ETNs are typically linked to the performance of a commodities index that reflects the potential return on unleveraged investments in futures contracts of physical commodities, plus a specified rate of interest that could be earned on cash collateral. ETNs are subject to credit risk. The value of an ETN may vary and may be influenced by time to maturity, level of supply and demand for the ETN, volatility and lack of liquidity in underlying commodities markets, changes in the applicable interest rates, changes in the issuer’s credit rating, and economic, legal, political, or geographic events that affect the referenced commodity. When an underlying fund invests in ETNs it will bear its proportionate share of any fees and expenses borne by the ETN. There may be restrictions on an underlying fund’s right to redeem its investment in an ETN, which is meant to be held until maturity. An underlying fund’s decision to sell its ETN holdings may be limited by the availability of a secondary market.

Derivatives Risk. Certain underlying funds may invest in derivatives. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

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The biggest risk is that the Fund’s returns will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

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An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

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PERFORMANCE INFORMATION

Performance Narrative [Text Block]

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The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares, the predecessor share class. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses in effect during the periods shown, net of any applicable fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. Performance information for each underlying fund is available in its prospectus and/or the most recent annual or semiannual report. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Performance Information Illustrates Variability of Returns [Text]

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The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

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The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-800-525-3713

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/allfunds

Performance Past Does Not Indicate Future [Text]

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The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

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Annual Total Returns for Class D Shares (calendar year-end)

Bar Chart Closing [Text Block]

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Best Quarter:  Second Quarter 2009  18.37%        Worst Quarter:  Fourth Quarter 2008  −18.05%

Year to Date Return, Label

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The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 11.53%.

Performance Table Heading

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Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

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After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

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Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Explanation after Tax Higher

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If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

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The Growth Allocation Index is an internally-calculated, hypothetical combination of unmanaged indices that combines total returns from the Dow Jones Wilshire 5000 Index (50%), the MSCI EAFE^® Index (25%), the Barclays U.S. Aggregate Bond Index (20%), and the Morgan Stanley Capital International Emerging Markets Free Index^sm (5%).

After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; and for the Fund’s Class J Shares, the predecessor share class, for the periods prior to February 16, 2010. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Closing [Text Block]

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Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Janus Growth Allocation Fund | Class D Shares | Class D

Risk/Return:

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Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class D

Management Fees

rr_ManagementFeesOverAssets

0.05%

Other Expenses

rr_OtherExpensesOverAssets

0.26%

^[1]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.76%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.07%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class D Shares

1 Year

rr_ExpenseExampleYear01

109

3 Years

rr_ExpenseExampleYear03

340

5 Years

rr_ExpenseExampleYear05

590

10 Years

rr_ExpenseExampleYear10

1,306

2006

rr_AnnualReturn2006

18.51%

2007

rr_AnnualReturn2007

15.73%

2008

rr_AnnualReturn2008

(34.91%)

2009

rr_AnnualReturn2009

35.79%

2010

rr_AnnualReturn2010

13.53%

2011

rr_AnnualReturn2011

(6.44%)

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

11.53%

Highest Quarterly Return, Label

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Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

18.37%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(18.05%)

Janus Growth Allocation Fund | Class D Shares | Return Before Taxes | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(6.44%)

5 Years

rr_AverageAnnualReturnYear05

1.67%

Since Inception

rr_AverageAnnualReturnSinceInception

4.30%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Growth Allocation Fund | Class D Shares | Return After Taxes on Distributions | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

(6.87%)

5 Years

rr_AverageAnnualReturnYear05

1.03%

Since Inception

rr_AverageAnnualReturnSinceInception

3.68%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Growth Allocation Fund | Class D Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[2]

1 Year

rr_AverageAnnualReturnYear01

(4.03%)

5 Years

rr_AverageAnnualReturnYear05

1.16%

Since Inception

rr_AverageAnnualReturnSinceInception

3.44%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Growth Allocation Fund | Class D Shares | S&P 500 Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

S&P 500^® Index

1 Year

rr_AverageAnnualReturnYear01

2.11%

5 Years

rr_AverageAnnualReturnYear05

(0.25%)

Since Inception

rr_AverageAnnualReturnSinceInception

2.26%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Growth Allocation Fund | Class D Shares | Growth Allocation Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Growth Allocation Index

1 Year

rr_AverageAnnualReturnYear01

(2.07%)

5 Years

rr_AverageAnnualReturnYear05

0.80%

Since Inception

rr_AverageAnnualReturnSinceInception

3.31%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

[1] Other Expenses are based on the estimated expenses that the Fund expects to incur.

[2] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Prospectus Date	rr_ProspectusDate	Oct. 26, 2012
Registrant Name	dei_EntityRegistrantName	JANUS INVESTMENT FUND
Perkins Select Value Fund | Class A, C, S, I, N, T Shares
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Fund summary Perkins Select Value Fund
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Perkins Select Value Fund seeks capital appreciation.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE FUND
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	SHAREHOLDER FEES (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	November 1, 2013
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover:
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the period December 15, 2011 to June 30, 2012, the Fund’s portfolio turnover rate was 80% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	80.00%
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 60 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	50,000
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE:
Expense Example by Year [Heading]	rr_ExpenseExampleByYearHeading	The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.
Expense Example by, Year, Caption [Text]	rr_ExpenseExampleByYearCaption	If Shares are redeemed:
Expense Example, No Redemption, By Year, Caption [Text]	rr_ExpenseExampleNoRedemptionByYearCaption	If Shares are not redeemed:
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Fund pursues its investment objective by investing primarily in common stocks selected for their capital appreciation potential. The Fund primarily invests in the common stocks of companies of any size whose stock prices the portfolio managers believe to be undervalued. The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets. In addition, when the portfolio managers believe that market conditions are unfavorable for investing, or when they are otherwise unable to locate attractive investment opportunities, the Fund’s cash or similar investments may increase. The Fund focuses on companies that have fallen out of favor with the market or that appear to be temporarily misunderstood by the investment community. The Fund’s portfolio managers generally look for companies with: strong balance sheets and solid recurring free cash flows attractive relative and absolute valuation ratios or that have underperformed recently favorable reward to risk characteristics The Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices, as substitutes for securities in which the Fund invests. The Fund may invest in derivative instruments (by taking long and/or short positions) for different purposes, including hedging (to offset risks associated with an investment, currency exposure, or market conditions) and to earn income and enhance returns. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.
Risk [Heading]	rr_RiskHeading	PRINCIPAL INVESTMENT RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices. Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s portfolio managers. When the Fund’s investments in cash or similar investments increase due to a lack of favorable investment opportunities or other extraordinary factors, the Fund may not participate in market advances or declines to the same extent that it would if the Fund had been fully invested. Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money. Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries. Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets. Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Risk Lose Money [Text]	rr_RiskLoseMoney	The biggest risk is that the Fund’s returns will vary, and you could lose money.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	PERFORMANCE INFORMATION
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The Fund does not have a full calendar year of operations. Performance information for certain periods is included in the Fund’s first annual and/or semiannual report.
Performance One Year or Less [Text]	rr_PerformanceOneYearOrLess	The Fund does not have a full calendar year of operations.
Perkins Select Value Fund | Class A, C, S, I, N, T Shares | Class A
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	Class A
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	5.75%
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class A
Management Fees (may adjust up or down)	rr_ManagementFeesOverAssets	0.70%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.56%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.51%	[1]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	0.24%	[1]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.27%	[1]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class A Shares
1 Year	rr_ExpenseExampleYear01	720
3 Years	rr_ExpenseExampleYear03	1,025
5 Years	rr_ExpenseExampleYear05	1,351
10 Years	rr_ExpenseExampleYear10	2,273
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class A Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	720
3 Years	rr_ExpenseExampleNoRedemptionYear03	1,025
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,351
10 Years	rr_ExpenseExampleNoRedemptionYear10	2,273
Perkins Select Value Fund | Class A, C, S, I, N, T Shares | Class C
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	Class C
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	1.00%
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class C
Management Fees (may adjust up or down)	rr_ManagementFeesOverAssets	0.70%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	0.73%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.43%	[1]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	0.41%	[1]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	2.02%	[1]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class C Shares
1 Year	rr_ExpenseExampleYear01	346
3 Years	rr_ExpenseExampleYear03	758
5 Years	rr_ExpenseExampleYear05	1,296
10 Years	rr_ExpenseExampleYear10	2,766
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class C Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	246
3 Years	rr_ExpenseExampleNoRedemptionYear03	758
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,296
10 Years	rr_ExpenseExampleNoRedemptionYear10	2,766
Perkins Select Value Fund | Class A, C, S, I, N, T Shares | Class S
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	Class S
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class S
Management Fees (may adjust up or down)	rr_ManagementFeesOverAssets	0.70%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.78%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.73%	[1]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	0.21%	[1]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.52%	[1]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class S Shares
1 Year	rr_ExpenseExampleYear01	176
3 Years	rr_ExpenseExampleYear03	545
5 Years	rr_ExpenseExampleYear05	939
10 Years	rr_ExpenseExampleYear10	2,041
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class S Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	176
3 Years	rr_ExpenseExampleNoRedemptionYear03	545
5 Years	rr_ExpenseExampleNoRedemptionYear05	939
10 Years	rr_ExpenseExampleNoRedemptionYear10	2,041
Perkins Select Value Fund | Class A, C, S, I, N, T Shares | Class I
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	Class I
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class I
Management Fees (may adjust up or down)	rr_ManagementFeesOverAssets	0.70%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.56%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.26%	[1]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	0.24%	[1]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.02%	[1]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class I Shares
1 Year	rr_ExpenseExampleYear01	128
3 Years	rr_ExpenseExampleYear03	400
5 Years	rr_ExpenseExampleYear05	692
10 Years	rr_ExpenseExampleYear10	1,523
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class I Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	128
3 Years	rr_ExpenseExampleNoRedemptionYear03	400
5 Years	rr_ExpenseExampleNoRedemptionYear05	692
10 Years	rr_ExpenseExampleNoRedemptionYear10	1,523
Perkins Select Value Fund | Class A, C, S, I, N, T Shares | Class N
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	Class N
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class N
Management Fees (may adjust up or down)	rr_ManagementFeesOverAssets	0.70%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.56%	[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.26%	[1]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	0.24%	[1]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.02%	[1]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class N Shares
1 Year	rr_ExpenseExampleYear01	128
3 Years	rr_ExpenseExampleYear03	400
5 Years	rr_ExpenseExampleYear05	692
10 Years	rr_ExpenseExampleYear10	1,523
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class N Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	128
3 Years	rr_ExpenseExampleNoRedemptionYear03	400
5 Years	rr_ExpenseExampleNoRedemptionYear05	692
10 Years	rr_ExpenseExampleNoRedemptionYear10	1,523
Perkins Select Value Fund | Class A, C, S, I, N, T Shares | Class T
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	Class T
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class T
Management Fees (may adjust up or down)	rr_ManagementFeesOverAssets	0.70%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.74%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.44%	[1]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	0.17%	[1]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.27%	[1]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class T Shares
1 Year	rr_ExpenseExampleYear01	147
3 Years	rr_ExpenseExampleYear03	456
5 Years	rr_ExpenseExampleYear05	787
10 Years	rr_ExpenseExampleYear10	1,724
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class T Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	147
3 Years	rr_ExpenseExampleNoRedemptionYear03	456
5 Years	rr_ExpenseExampleNoRedemptionYear05	787
10 Years	rr_ExpenseExampleNoRedemptionYear10	1,724

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding any performance adjustments to management fees, the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, and Class S Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 1.00% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

[2] Other Expenses for Class N Shares are based on the estimated expenses that the Shares expect to incur during their initial fiscal period.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Perkins Mid Cap Value Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Perkins Mid Cap Value Fund seeks capital appreciation.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

SHAREHOLDER FEES
(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

November 1, 2013

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 54% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

54.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 60 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

If Shares are redeemed:

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

If Shares are not redeemed:

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund pursues its investment objective by investing primarily in common stocks selected for their capital appreciation potential. The Fund primarily invests in the common stocks of mid-sized companies whose stock prices the portfolio managers believe to be undervalued. The Fund invests, under normal circumstances, at least 80% of its net assets in equity securities of companies whose market capitalization falls, at the time of purchase, within the 12-month average of the capitalization range of the Russell Midcap^® Value Index. This average is updated monthly. The market capitalizations within the index will vary, but as of June 30, 2012, they ranged from approximately $1.3 billion to $18.5 billion. The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets. The Fund may invest, under normal circumstances, up to 20% of its net assets in securities of companies having market capitalizations outside of the aforementioned market capitalization ranges. In addition, when the portfolio managers believe that market conditions are unfavorable for investing, or when they are otherwise unable to locate attractive investment opportunities, the Fund may invest up to 20% of its net assets in cash or similar investments.

The Fund focuses on companies that have fallen out of favor with the market or that appear to be temporarily misunderstood by the investment community. The Fund’s portfolio managers generally look for companies with:

•   strong balance sheets and solid recurring free cash flows
•   attractive relative and absolute valuation ratios or that have underperformed recently
•   favorable reward to risk characteristics

The Fund may also invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. The Fund has and is expected to continue to buy and sell put and call options, particularly on market indices, for hedging purposes (to offset risks associated with an investment, currency exposure, or market conditions) and to enhance returns. The Fund’s exposure to derivatives will vary, is not limited to those derivatives listed, and could be significant at times. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s portfolio managers. When the Fund’s investments in cash or similar investments increase due to a lack of favorable investment opportunities or other extraordinary factors, the Fund may not participate in market advances or declines to the same extent that it would if the Fund had been fully invested.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Mid-Sized Companies Risk. The Fund’s investments in securities issued by mid-sized companies may involve greater risks than are customarily associated with larger, more established companies. Securities issued by mid-sized companies tend to be more volatile than securities issued by larger or more established companies and may underperform as compared to the securities of larger companies.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

The biggest risk is that the Fund’s returns will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class R Shares of the Fund commenced operations on July 6, 2009. Class N Shares of the Fund commenced operations on May 31, 2012.

•  The performance shown for Class T Shares for periods following April 21, 2003, reflects the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class T Shares reflects the historical performance of Berger Mid Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Mid Cap Value Fund – Investor Shares into the Fund’s former Class J Shares).
•  The performance shown for Class A Shares, Class C Shares, Class S Shares, and Class R Shares reflects the performance of the Fund’s Class J Shares (formerly named Investor Shares) from April 21, 2003 to July 6, 2009, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers. For periods prior to April 21, 2003, the performance shown for Class A Shares, Class C Shares, Class S Shares, and Class R Shares reflects the historical performance of Berger Mid Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Mid Cap Value Fund – Investor Shares into the Fund’s former Class J Shares), calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers.
•  The performance shown for Class I Shares reflects the performance of the Fund’s Class J Shares (formerly named Investor Shares) from April 21, 2003 to July 6, 2009, calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class I Shares reflects the historical performance of Berger Mid Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Mid Cap Value Fund – Investor Shares into the Fund’s former Class J Shares), calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers.
•  The performance shown for Class N Shares reflects the performance of the Fund’s Class T Shares from July 6, 2009 to December 31, 2011, calculated using the fees and expenses of Class T Shares, net of any applicable fee and expense limitations or waivers. For the period from April 21, 2003 to July 6, 2009, the performance shown for Class N Shares reflects the performance of the Fund’s Class J Shares (formerly named Investor Shares), calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class N Shares reflects the historical performance of Berger Mid Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Mid Cap Value Fund – Investor Shares into the Fund’s former Class J Shares), calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers.

If Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class R Shares of the Fund had been available during periods prior to July 6, 2009, or Class N Shares of the Fund had been available during periods prior to December 31, 2011, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, Class I Shares, Class N Shares, and Class R Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-877-335-2687

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/advisor/mutual-funds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class T Shares (calendar year-end)

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter: Second Quarter 2003 17.17%           Worst Quarter: Fourth Quarter 2008 −19.63%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 9.06%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares) for the periods following April 21, 2003; and for Berger Mid Cap Value Fund – Investor Shares for periods prior to April 21, 2003. If Class T Shares of the Fund had been available during the periods prior to April 21, 2003, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Class A

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class A

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class A

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.54%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.26%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.05%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.04%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.01%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleYear01

676

3 Years

rr_ExpenseExampleYear03

890

5 Years

rr_ExpenseExampleYear05

1,121

10 Years

rr_ExpenseExampleYear10

1,784

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

676

3 Years

rr_ExpenseExampleNoRedemptionYear03

890

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,121

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,784

Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Class C

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class C

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

1.00%

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class C

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.54%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

0.24%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.78%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.02%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.76%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleYear01

281

3 Years

rr_ExpenseExampleYear03

560

5 Years

rr_ExpenseExampleYear05

964

10 Years

rr_ExpenseExampleYear10

2,095

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

181

3 Years

rr_ExpenseExampleNoRedemptionYear03

560

5 Years

rr_ExpenseExampleNoRedemptionYear05

964

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,095

Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Class S

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class S

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class S

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.54%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.30%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.09%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

none

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.09%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleYear01

111

3 Years

rr_ExpenseExampleYear03

347

5 Years

rr_ExpenseExampleYear05

601

10 Years

rr_ExpenseExampleYear10

1,329

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

111

3 Years

rr_ExpenseExampleNoRedemptionYear03

347

5 Years

rr_ExpenseExampleNoRedemptionYear05

601

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,329

Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class I

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class I

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.54%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.19%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.73%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

none

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.73%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleYear01

75

3 Years

rr_ExpenseExampleYear03

233

5 Years

rr_ExpenseExampleYear05

406

10 Years

rr_ExpenseExampleYear10

906

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

75

3 Years

rr_ExpenseExampleNoRedemptionYear03

233

5 Years

rr_ExpenseExampleNoRedemptionYear05

406

10 Years

rr_ExpenseExampleNoRedemptionYear10

906

Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Class N

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class N

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class N

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.54%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.04%

^[2]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.58%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

none

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.58%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class N Shares

1 Year

rr_ExpenseExampleYear01

59

3 Years

rr_ExpenseExampleYear03

186

5 Years

rr_ExpenseExampleYear05

324

10 Years

rr_ExpenseExampleYear10

726

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class N Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

59

3 Years

rr_ExpenseExampleNoRedemptionYear03

186

5 Years

rr_ExpenseExampleNoRedemptionYear05

324

10 Years

rr_ExpenseExampleNoRedemptionYear10

726

Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Class R

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class R

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class R

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.54%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.50%

Other Expenses

rr_OtherExpensesOverAssets

0.30%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.34%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

none

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.34%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class R Shares

1 Year

rr_ExpenseExampleYear01

136

3 Years

rr_ExpenseExampleYear03

425

5 Years

rr_ExpenseExampleYear05

734

10 Years

rr_ExpenseExampleYear10

1,613

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class R Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

136

3 Years

rr_ExpenseExampleNoRedemptionYear03

425

5 Years

rr_ExpenseExampleNoRedemptionYear05

734

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,613

Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class T

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.54%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.30%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.84%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

none

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.84%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleYear01

86

3 Years

rr_ExpenseExampleYear03

268

5 Years

rr_ExpenseExampleYear05

466

10 Years

rr_ExpenseExampleYear10

1,037

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

86

3 Years

rr_ExpenseExampleNoRedemptionYear03

268

5 Years

rr_ExpenseExampleNoRedemptionYear05

466

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,037

2002

rr_AnnualReturn2002

(13.09%)

2003

rr_AnnualReturn2003

39.33%

2004

rr_AnnualReturn2004

18.36%

2005

rr_AnnualReturn2005

10.36%

2006

rr_AnnualReturn2006

15.25%

2007

rr_AnnualReturn2007

7.43%

2008

rr_AnnualReturn2008

(27.33%)

2009

rr_AnnualReturn2009

30.37%

2010

rr_AnnualReturn2010

14.81%

2011

rr_AnnualReturn2011

(2.55%)

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

9.06%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2003

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

17.17%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(19.63%)

Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class A

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class A Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[3]

1 Year

rr_AverageAnnualReturnYear01

(8.32%)

5 Years

rr_AverageAnnualReturnYear05

1.24%

10 Years

rr_AverageAnnualReturnYear10

6.75%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

11.12%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 12, 1998

Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class C

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class C Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[4]

1 Year

rr_AverageAnnualReturnYear01

(4.27%)

5 Years

rr_AverageAnnualReturnYear05

1.71%

10 Years

rr_AverageAnnualReturnYear10

6.62%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

10.90%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 12, 1998

Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class S

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class S Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(2.73%)

5 Years

rr_AverageAnnualReturnYear05

2.34%

10 Years

rr_AverageAnnualReturnYear10

7.27%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

11.51%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 12, 1998

Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(2.43%)

5 Years

rr_AverageAnnualReturnYear05

2.63%

10 Years

rr_AverageAnnualReturnYear10

7.58%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

11.76%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 12, 1998

Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class N

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class N Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(2.55%)

5 Years

rr_AverageAnnualReturnYear05

2.63%

10 Years

rr_AverageAnnualReturnYear10

7.58%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

11.76%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 12, 1998

Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class R

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class R Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(3.01%)

5 Years

rr_AverageAnnualReturnYear05

2.08%

10 Years

rr_AverageAnnualReturnYear10

7.00%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

11.29%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 12, 1998

Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(2.55%)

5 Years

rr_AverageAnnualReturnYear05

2.63%

10 Years

rr_AverageAnnualReturnYear10

7.58%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

11.76%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 12, 1998

Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return After Taxes on Distributions | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

(3.88%)

5 Years

rr_AverageAnnualReturnYear05

1.63%

10 Years

rr_AverageAnnualReturnYear10

6.48%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

10.31%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 12, 1998

Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[5]

1 Year

rr_AverageAnnualReturnYear01

(0.18%)

5 Years

rr_AverageAnnualReturnYear05

2.04%

10 Years

rr_AverageAnnualReturnYear10

6.34%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

9.94%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 12, 1998

Perkins Mid Cap Value Fund | Class A, C, S, I, N, R, T Shares | Russell Midcap Value Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Russell Midcap^® Value Index

1 Year

rr_AverageAnnualReturnYear01

(1.38%)

5 Years

rr_AverageAnnualReturnYear05

0.04%

10 Years

rr_AverageAnnualReturnYear10

7.67%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

7.70%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 12, 1998

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding any performance adjustments to management fees, the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, Class S Shares, and Class R Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 0.86% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

[2] Other Expenses for Class N Shares are based on the estimated expenses that the Shares expect to incur during their initial fiscal period.

[3] Calculated assuming maximum permitted sales loads.

[4] The one year return is calculated to include the contingent deferred sales charge.

[5] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Janus World Allocation Fund | Class A, C, S, I, T Shares

Fund summary

Janus World Allocation Fund

INVESTMENT OBJECTIVE

Janus World Allocation Fund seeks long-term growth of capital with a secondary emphasis on income.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 31 of the Fund’s Prospectus and in the “Purchases” section on page 64 of the Fund’s Statement of Additional Information.

SHAREHOLDER FEES
(fees paid directly from your investment)

Shareholder Fees Janus World Allocation Fund Class A, C, S, I, T Shares

Class A

Class C

Class S

Class I

Class T

Shareholder Fees Column [Text]

Class A

Class C

Class S

Class I

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

5.75%

none

none

none

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

none

1.00%

none

none

none

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Janus World Allocation Fund Class A, C, S, I, T Shares

Class A

Class C

Class S

Class I

Class T

Operating Expenses Column [Text]

Class A

Class C

Class S

Class I

Class T

Management Fees

0.07%

0.07%

0.07%

0.07%

0.07%

Distribution/Service (12b-1) Fees

0.25%

1.00%

0.25%

none

none

Other Expenses

1.73%

1.84%

1.96%

1.76%

1.89%

Acquired Fund Fees and Expenses

0.74%

0.74%

0.74%

0.74%

0.74%

Total Annual Fund Operating Expenses

^[1]

2.79%

3.65%

3.02%

2.57%

2.70%

Fee Waiver

^[1]

1.33%

1.44%

1.31%

1.36%

1.24%

Total Annual Fund Operating Expenses After Fee Waiver

^[1]

1.46%

2.21%

1.71%

1.21%

1.46%

EXAMPLE:

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses (including the operating expenses of the underlying funds) without waivers remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

If Shares are redeemed:

Expense Example Janus World Allocation Fund Class A, C, S, I, T Shares (USD $)

Expense Example, By Year, Column [Text]

1 Year

3 Years

5 Years

10 Years

Class A

Class A Shares

841

1,390

1,964

3,514

Class C

Class C Shares

467

1,117

1,888

3,906

Class S

Class S Shares

305

933

1,587

3,337

Class I

Class I Shares

260

799

1,365

2,905

Class T

Class T Shares

273

838

1,430

3,032

If Shares are not redeemed:

Expense Example, No Redemption Janus World Allocation Fund Class A, C, S, I, T Shares (USD $)

Expense Example, No Redemption, By Year, Column [Text]

1 Year

3 Years

5 Years

10 Years

Class A

Class A Shares

841

1,390

1,964

3,514

Class C

Class C Shares

367

1,117

1,888

3,906

Class S

Class S Shares

305

933

1,587

3,337

Class I

Class I Shares

260

799

1,365

2,905

Class T

Class T Shares

273

838

1,430

3,032

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 36% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objective by investing in a diversified portfolio of other Janus mutual funds (“underlying funds”) and securities that provide exposure to issuers located throughout the world. Through its investment in the underlying funds, the Fund invests in issuers from several different countries, including the United States, and may, under unusual circumstances, be invested in a single country. The Fund may also have significant exposure to emerging markets. Because it invests in other funds, the Fund is considered a “fund of funds.” The Fund utilizes Janus Capital’s proprietary process to allocate assets across the following three asset categories (as defined by Janus Capital):

•   Core – The Core category seeks to provide market-like exposure by investing in funds that in turn primarily invest in a broad range of traditional asset classes such as large-, mid-, and small-cap stocks, U.S. and non-U.S. stocks, growth and value stocks, and investment-grade bonds. While not a primary strategy, the underlying funds may also invest in emerging market stocks and high-yield bonds. A primary goal of the underlying funds in the Core category is to provide shareholders with access to a broad range of investable assets in proportion to each asset class’ representation in today’s global, integrated market as determined by Janus Capital.

•   Alpha – The Alpha category seeks to generate higher-than-market returns on a risk-adjusted basis by investing in funds that in turn invest in a broad range of traditional asset classes such as large-, mid-, and small-cap stocks, U.S. and non-U.S. stocks, growth and value stocks, emerging market stocks, investment-grade bonds, and high-yield bonds. Unlike funds in the Core category, the Alpha category is less focused on the asset class composition of the global market. Instead, the Alpha category is comprised of funds, unconstrained by asset class or investment style, that Janus Capital believes may generate higher-than-market returns over a market cycle.

•   Alternative – The Alternative category is comprised of non-traditional investments with historically low correlation to the assets in the Core and Alpha categories, such as certain exchange-traded funds (“ETFs”), exchange-traded notes (“ETNs”), investments with hedge fund strategy exposure, commodities-related securities, real estate-related securities, and structured products.

The Fund attempts to maximize returns by investing the Fund’s assets in underlying funds investing in stocks (U.S. and non-U.S.), bonds, cash equivalents, alternative asset classes (such as real estate-related securities and commodity-related securities), and alternative investment strategies (such as leveraged and sector-based strategies). The target allocation of the Fund’s assets among underlying funds is based on an optimization process that utilizes quantitative analysis of a number of factors, such as historical risk, performance, fund classifications, and the relationship among underlying funds, as well as the portfolio manager’s judgment. Janus Capital analyzes Fund allocations on a regular basis in order to integrate current market data and reallocates on a quarterly basis.

The Fund’s portfolio manager determines the overall composition of the Fund, oversees the investment process, and is responsible for the day-to-day management of the Fund. The portfolio manager consults with a committee comprised of Janus Capital investment professionals (“Asset Allocation Committee”) to regularly review the process and the allocation of the Fund’s assets among the underlying funds to determine modifications to the underlying funds’ asset categories and/or weightings, or to substitute other underlying funds to emphasize and mitigate risk exposures that may arise as a result of the implementation of the allocations. The portfolio manager and Asset Allocation Committee normally review asset allocations on a quarterly basis. The portfolio manager oversees the implementation of trades on behalf of the Fund.

The Fund’s investments will be rebalanced to the identified optimal weightings on a quarterly basis, although more frequent changes can occur. The Fund’s asset class or category, category allocations, underlying funds, or underlying fund weightings may change without prior shareholder notice.

The Fund will normally allocate approximately 90% of its assets to Janus-managed mutual funds and approximately 10% to unaffiliated pooled investment vehicles (e.g., ETFs) and derivatives. For information on the potential underlying Janus funds currently available for investment by the Fund, including investment objectives and strategies, see “Investment Objectives and Strategies of the Underlying Funds” in Appendix A.

The Fund may invest in ETFs and ETNs to complement its investment in the underlying funds if there are asset classes not covered by the underlying funds or to better manage cash positions.

The Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices, as substitutes for securities in which the Fund invests. The Fund may invest in derivative instruments (by taking long and/or short positions) including, but not limited to, swap agreements to earn income and enhance uncorrelated returns, to increase or decrease exposure to a particular market, to manage or adjust the risk profile of the Fund, or as alternatives to direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

When market conditions dictate a more defensive strategy, the Fund or an underlying fund may temporarily hold cash or invest its assets in temporary investments. In that case, the Fund may take positions that are inconsistent with its investment objective. As a result, the Fund may not achieve its investment objective.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking growth of capital and, to a lesser extent, income. Investments in a portfolio with common stock and alternative investment exposure tend to be more volatile than many other investment choices.

Main Risks Associated with the Fund
Allocation Risk. The Fund’s ability to achieve its investment objective depends largely upon the portfolio manager’s allocation of assets among the underlying funds and other securities, using the optimization process and the judgment of the portfolio manager. You could lose money on your investment in the Fund as a result of these allocations. The Fund will typically invest in a number of different underlying funds; however, to the extent that the Fund invests a significant portion of its assets in a single underlying fund, it will be more sensitive to the risks associated with that fund and any investments in which that fund concentrates.

Derivatives Risk. The Fund and certain underlying funds may invest in derivatives. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

Commodity-Linked Derivative Investment Risk. The Fund may invest in derivatives that have exposure to the commodities markets. This exposure may subject the Fund to greater volatility than investments in traditional securities. The value of a commodity-linked derivative investment typically is based upon the price movements of a physical commodity (such as heating oil, livestock, or agricultural products), a commodity futures contract or commodity index, or some other readily measurable economic variable. The value of commodity-linked derivative instruments may therefore be affected by changes in overall market movements, volatility of the underlying benchmark, changes in interest rates, or other factors affecting a particular industry or commodity such as drought, floods, weather, livestock disease, embargoes, tariffs, and international economic, political, and regulatory developments.

Exchange-Traded Funds Risk. The Fund may purchase shares of ETFs to gain exposure to a particular portion of the market. ETFs are pooled investment vehicles, which may be managed or unmanaged, that generally seek to track the performance of a specific index. ETFs are traded on an exchange at market prices that may vary from the net asset value of their underlying investments. When the Fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF’s expenses. ETFs have certain inherent risks generally associated with investments in a portfolio of securities in which the ETF is invested, including the risk that the general level of stock prices may decline, thereby adversely affecting the value of each unit of the ETF. ETFs also involve the risk that an active trading market for an ETF’s shares may not develop or be maintained.

Affiliated Fund Risk. Janus Capital has the authority to select and substitute underlying affiliated mutual funds. The fees paid to Janus Capital by some Janus mutual funds are generally higher than the fees paid to Janus Capital by the Fund or by other funds and share classes available for investment by the Fund. These conditions may create a conflict of interest when selecting underlying affiliated mutual funds and share classes for investment. Janus Capital, however, is a fiduciary to the Fund and its shareholders and is legally obligated to act in their best interest when selecting underlying affiliated mutual funds.

Main Risks Associated with the Underlying Funds and Securities
The biggest risk is that the underlying funds’ returns will vary, and you could lose money.

Market Risk. Underlying funds investing in equity securities are subject to the risks associated with investments in common stocks, which tend to be more volatile than many other investment choices. The value of an underlying fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if a portfolio manager’s belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of an underlying fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Fixed-Income Securities Risk. Through the Fund’s investments in underlying funds holding fixed-income securities, the Fund is subject to the risks associated with investments in a variety of fixed-income securities, which may be less volatile than underlying funds that invest most of their assets in common stocks; returns and yields will vary, and you could lose money. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause an underlying fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which an underlying fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that an underlying fund’s portfolio manager would like or at the price that the portfolio manager believes the security is currently worth.

Foreign Exposure Risk. The Fund and certain underlying funds may have significant exposure to foreign markets as a result of their investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, the Fund’s and an underlying fund’s returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. A market swing in one or more countries or regions where the Fund or an underlying fund has invested a significant amount of its assets may have a greater effect on the Fund’s or an underlying Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s or an underlying fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Emerging Markets Risk. The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities involve a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. In addition, the Fund’s or an underlying fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of the Fund’s or an underlying fund’s investments. To the extent that the Fund or an underlying fund invests a significant portion of its assets in the securities of issuers in or companies of a single country or region, it is more likely to be impacted by events or conditions affecting that country or region, which could have a negative impact on the Fund’s performance. Some of the risks of investing directly in foreign and emerging market securities may be reduced when the Fund or an underlying fund invests indirectly in foreign securities through various other investment vehicles including derivatives, which also involve other risks.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Sovereign Debt Risk. An underlying fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class I Shares, Class A Shares, Class C Shares, and Class S Shares of the Fund commenced operations on July 6, 2009, after the reorganization of each corresponding class of shares of Janus Adviser Modular Portfolio Construction^® Fund (“JAD predecessor fund”) into each respective share class of the Fund. Class T Shares of the Fund commenced operations on July 6, 2009.

• The performance shown for Class I Shares, Class A Shares, Class C Shares, and Class S Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund’s Class I Shares, Class A Shares, Class C Shares and Class S Shares prior to the reorganization, calculated using the fees and expenses of each respective share class of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class T Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund’s Class I Shares prior to the reorganization, calculated using the fees and expenses of Class T Shares, without the effect of any fee and expense limitations or waivers.

If Class T Shares of the Fund had been available during periods prior to July 6, 2009, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class I Shares, Class A Shares, Class C Shares, Class S Shares, and Class T Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. Performance information for each underlying fund is available in its prospectus and/or the most recent annual or semiannual report. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Annual Total Returns for Class I Shares (calendar year-end)

Best Quarter:  Second Quarter 2009  14.90%          Worst Quarter:  Third Quarter 2011  −13.38%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 8.19%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Janus World Allocation Fund Class A, C, S, I, T Shares

Column

Label

1 Year

Since Inception of Predecessor Fund

Inception Date

Class I Shares Return Before Taxes

Class I Shares

Return Before Taxes

(8.00%)

0.06%

Sep. 03, 2008

Class I Shares Return After Taxes on Distributions

Class I Shares

Return After Taxes on Distributions

(9.03%)

(0.71%)

Sep. 03, 2008

Class I Shares Return After Taxes on Distributions and Sale of Fund Shares

Class I Shares

Return After Taxes on Distributions and Sale of Fund Shares

^[1]

(4.11%)

(0.15%)

Sep. 03, 2008

Class A Shares Return Before Taxes

Class A Shares

Return Before Taxes

^[2]

(13.24%)

(1.79%)

Sep. 03, 2008

Class C Shares Return Before Taxes

Class C Shares

Return Before Taxes

^[3]

(9.46%)

(0.62%)

Sep. 03, 2008

Class S Shares Return Before Taxes

Class S Shares

Return Before Taxes

(8.07%)

(0.19%)

Sep. 03, 2008

Class T Shares Return Before Taxes

Class T Shares

Return Before Taxes

(7.87%)

0.03%

Sep. 03, 2008

Morgan Stanley Capital International All Country World Index (net of foreign withholding taxes) (reflects no deduction for expenses, fees, or taxes, except foreign withholding taxes)

Morgan Stanley Capital International All Country World Index^sm (net of foreign withholding taxes)

(7.35%)

(0.71%)

Sep. 03, 2008

World Allocation Index (reflects no deduction for expenses, fees, or taxes)

World Allocation Index

(2.72%)

2.25%

Sep. 03, 2008

The World Allocation Index is an internally-calculated, hypothetical combination of unmanaged indices that combines total returns from the MSCI All Country World Index^sm (65%) and the Barclays Global Aggregate Bond Index (35%).

After-tax returns are calculated using distributions for the Fund’s Class I Shares for periods following July 6, 2009; and for the JAD predecessor fund’s Class I Shares for periods prior to July 6, 2009. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding any expenses of an underlying fund (acquired fund fees and expenses), the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, and Class S Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; and extraordinary expenses) to 0.45% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

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Registrant Name

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JANUS INVESTMENT FUND

Prospectus Date

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Oct. 26, 2012

Janus Conservative Allocation Fund | Class D Shares

Risk/Return:

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Risk/Return [Heading]

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Fund summary

Janus Conservative Allocation Fund

Objective [Heading]

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INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

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Janus Conservative Allocation Fund seeks total return through a primary emphasis on income with a secondary emphasis on growth of capital.

Expense [Heading]

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FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

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This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

Operating Expenses Caption [Text]

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ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

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Portfolio Turnover:

Portfolio Turnover [Text Block]

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The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 10% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

10.00%

Expense Example [Heading]

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EXAMPLE:

Expense Example by Year [Heading]

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The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses (including the operating expenses of the underlying funds) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

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The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Strategy [Heading]

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PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

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The Fund seeks to achieve its investment objective by investing in other Janus mutual funds (“underlying funds”) that represent a variety of asset classes and investment styles. The Fund pursues this objective by investing in a diversified portfolio of underlying funds resulting in an allocation of the Fund’s investments that normally provides exposure of approximately 40% to stocks and 60% to bonds and money market securities. The target allocation and the allocation of the Fund’s assets among underlying funds are based on quantitative and qualitative analysis. Because it invests in other funds, the Fund is considered a “fund of funds.”

The Fund’s asset allocation is intended to diversify investments among stocks, bonds, and cash equivalents. The portfolio manager regularly reviews the allocation of Fund assets in the underlying funds and may modify the underlying funds’ weightings or substitute other underlying funds to emphasize and mitigate risk exposures that may arise as a result of the implementation of the allocations. An independent asset allocation service provides evaluations of asset allocations that the portfolio manager may use in implementing the allocations among the underlying funds. The portfolio manager continually monitors asset class allocations and periodically rebalances the Fund’s investments in the underlying funds. The portfolio manager may change the Fund’s asset class allocations, the underlying funds, an underlying fund’s asset category, or weightings among asset classes or underlying funds without prior shareholder notice.

The Fund will normally allocate approximately 60% of its investments to underlying bond funds and money market instruments; and approximately 40% of its investments to underlying funds that provide varying exposure to common stocks of large U.S.-based companies, small- to mid-capitalization companies, and international companies (including those with exposure to emerging markets). Refer to Appendix A in this Prospectus for a brief description of the investment strategies of each of the currently available underlying funds.

When market conditions dictate a more defensive strategy, the Fund or an underlying fund may temporarily hold cash or invest its assets in temporary investments. In that case, the Fund may take positions that are inconsistent with its investment objective. As a result, the Fund may not achieve its investment objective.

Risk [Heading]

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PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

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The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking income and, to a lesser extent, growth of capital. Investments in a portfolio with common stock exposure tend to be more volatile than many other investment choices.

Main Risks Associated with the Fund
Allocation Risk. The Fund’s ability to achieve its investment objective depends largely upon the portfolio manager’s allocation of assets among the underlying funds and other securities, using the optimization process (a process that utilizes quantitative analysis of a number of factors, such as historical risk, performance, fund classifications, and the relationship among underlying funds) and the judgment of the portfolio manager. You could lose money on your investment in the Fund as a result of these allocations. The Fund will typically invest in a number of different underlying funds; however, to the extent that the Fund invests a significant portion of its assets in a single underlying fund, it will be more sensitive to the risks associated with that fund and any investments in which that fund concentrates.

Affiliated Fund Risk. Janus Capital has the authority to select and substitute underlying affiliated mutual funds. The fees paid to Janus Capital by some Janus mutual funds are generally higher than the fees paid to Janus Capital by the Fund or by other funds and share classes available for investment by the Fund. These conditions may create a conflict of interest when selecting underlying affiliated mutual funds and share classes for investment. Janus Capital, however, is a fiduciary to the Fund and its shareholders and is legally obligated to act in their best interest when selecting underlying affiliated mutual funds.

Main Risks Associated with the Underlying Funds and Securities
The biggest risk is that the underlying funds’ returns will vary, and you could lose money.

Fixed-Income Securities Risk. Approximately 60% of the Fund’s assets are allocated to fixed-income securities through investments in underlying funds. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause an underlying fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which an underlying fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that an underlying fund’s portfolio manager would like or at the price that the portfolio manager believes the security is currently worth.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Market Risk. Approximately 40% of the Fund’s assets are allocated to equity investments through investments in underlying funds. The value of an underlying fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if a portfolio manager’s belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of an underlying fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Foreign Exposure Risk. Certain underlying funds may have significant exposure to foreign markets as a result of their investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, an underlying fund’s returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. A market swing in one or more countries or regions where an underlying fund has invested a significant amount of its assets may have a greater effect on an underlying fund’s performance than it would in a more geographically diversified portfolio. An underlying fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Emerging Markets Risk. The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities involve a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. In addition, an underlying fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of an underlying fund’s investments. To the extent that an underlying fund invests a significant portion of its assets in the securities of issuers in or companies of a single country or region, it is more likely to be impacted by events or conditions affecting that country or region, which could have a negative impact on the Fund’s performance. Some of the risks of investing directly in foreign and emerging market securities may be reduced when an underlying fund invests indirectly in foreign securities through various other investment vehicles including derivatives, which also involve other risks.

Sovereign Debt Risk. An underlying fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

Exchange-Traded Funds Risk. Certain underlying funds may purchase shares of exchange-traded funds (“ETFs”) to gain exposure to a particular portion of the market. ETFs are pooled investment vehicles, which may be managed or unmanaged, that generally seek to track the performance of a specific index. ETFs are traded on an exchange at market prices that may vary from the net asset value of their underlying investments. When an underlying fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF’s expenses. ETFs have certain inherent risks generally associated with investments in a portfolio of securities in which the ETF is invested, including the risk that the general level of stock prices may decline, thereby adversely affecting the value of each unit of the ETF. ETFs also involve the risk that an active trading market for an ETF’s shares may not develop or be maintained.

Exchange-Traded Notes Risk. Certain underlying funds may invest in exchange-traded notes (“ETNs”), which are debt securities whose returns are linked to a particular index. ETNs are typically linked to the performance of a commodities index that reflects the potential return on unleveraged investments in futures contracts of physical commodities, plus a specified rate of interest that could be earned on cash collateral. ETNs are subject to credit risk. The value of an ETN may vary and may be influenced by time to maturity, level of supply and demand for the ETN, volatility and lack of liquidity in underlying commodities markets, changes in the applicable interest rates, changes in the issuer’s credit rating, and economic, legal, political, or geographic events that affect the referenced commodity. When an underlying fund invests in ETNs it will bear its proportionate share of any fees and expenses borne by the ETN. There may be restrictions on an underlying fund’s right to redeem its investment in an ETN, which is meant to be held until maturity. An underlying fund’s decision to sell its ETN holdings may be limited by the availability of a secondary market.

Derivatives Risk. Certain underlying funds may invest in derivatives. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

The biggest risk is that the Fund’s returns will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares, the predecessor share class. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses in effect during the periods shown, net of any applicable fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. Performance information for each underlying fund is available in its prospectus and/or the most recent annual or semiannual report. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-800-525-3713

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/allfunds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class D Shares (calendar year-end)

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Second Quarter 2009  10.64%          Worst Quarter:  Third Quarter 2008  −6.58%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 9.32%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The Conservative Allocation Index is an internally-calculated, hypothetical combination of unmanaged indices that combines total returns from the Barclays U.S. Aggregate Bond Index (60%), the Dow Jones Wilshire 5000 Index (28%), and the Morgan Stanley Capital International Europe, Australasia, Far East Index (“MSCI EAFE^®”) Index (12%).

After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; and for the Fund’s Class J Shares, the predecessor share class, for the periods prior to February 16, 2010. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Janus Conservative Allocation Fund | Class D Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class D

Management Fees

rr_ManagementFeesOverAssets

0.05%

Other Expenses

rr_OtherExpensesOverAssets

0.22%

^[1]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.64%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.91%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class D Shares

1 Year

rr_ExpenseExampleYear01

93

3 Years

rr_ExpenseExampleYear03

290

5 Years

rr_ExpenseExampleYear05

504

10 Years

rr_ExpenseExampleYear10

1,120

2006

rr_AnnualReturn2006

11.09%

2007

rr_AnnualReturn2007

10.19%

2008

rr_AnnualReturn2008

(16.01%)

2009

rr_AnnualReturn2009

23.37%

2010

rr_AnnualReturn2010

10.69%

2011

rr_AnnualReturn2011

1.51%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

9.32%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

10.64%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(6.58%)

Janus Conservative Allocation Fund | Class D Shares | Return Before Taxes | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

1.51%

5 Years

rr_AverageAnnualReturnYear05

5.11%

Since Inception

rr_AverageAnnualReturnSinceInception

6.08%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Conservative Allocation Fund | Class D Shares | Return After Taxes on Distributions | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

0.54%

5 Years

rr_AverageAnnualReturnYear05

4.00%

Since Inception

rr_AverageAnnualReturnSinceInception

5.03%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Conservative Allocation Fund | Class D Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[2]

1 Year

rr_AverageAnnualReturnYear01

1.07%

5 Years

rr_AverageAnnualReturnYear05

3.76%

Since Inception

rr_AverageAnnualReturnSinceInception

4.66%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Conservative Allocation Fund | Class D Shares | S&P 500 Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

S&P 500^® Index

1 Year

rr_AverageAnnualReturnYear01

2.11%

5 Years

rr_AverageAnnualReturnYear05

(0.25%)

Since Inception

rr_AverageAnnualReturnSinceInception

2.26%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Conservative Allocation Fund | Class D Shares | Conservative Allocation Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Conservative Allocation Index

1 Year

rr_AverageAnnualReturnYear01

3.61%

5 Years

rr_AverageAnnualReturnYear05

3.89%

Since Inception

rr_AverageAnnualReturnSinceInception

4.89%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

[1] Other Expenses are based on the estimated expenses that the Fund expects to incur.

[2] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

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Perkins Large Cap Value Fund | Class A, C, S, I, N, T Shares

Fund summary

Perkins Large Cap Value Fund

INVESTMENT OBJECTIVE

Perkins Large Cap Value Fund seeks capital appreciation.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 60 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.

SHAREHOLDER FEES
(fees paid directly from your investment)

Shareholder Fees Perkins Large Cap Value Fund Class A, C, S, I, N, T Shares

Class A

Class C

Class S

Class I

Class N

Class T

Shareholder Fees Column [Text]

Class A

Class C

Class S

Class I

Class N

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

5.75%

none

none

none

none

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

none

1.00%

none

none

none

none

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Perkins Large Cap Value Fund Class A, C, S, I, N, T Shares

Class A

Class C

Class S

Class I

Class N

Class T

Operating Expenses Column [Text]

Class A

Class C

Class S

Class I

Class N

Class T

Management Fees (may adjust up or down)

0.62%

0.62%

0.62%

0.62%

0.62%

0.62%

Distribution/Service (12b-1) Fees

0.25%

1.00%

0.25%

none

none

none

Other Expenses

0.26%

0.30%

0.38%

0.15%

0.14%

^[1]

0.38%

Total Annual Fund Operating Expenses

1.13%

1.92%

1.25%

0.77%

0.76%

1.00%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

If Shares are redeemed:

Expense Example Perkins Large Cap Value Fund Class A, C, S, I, N, T Shares (USD $)

Expense Example, By Year, Column [Text]

1 Year

3 Years

5 Years

10 Years

Class A

Class A Shares

684

913

1,161

1,871

Class C

Class C Shares

295

603

1,037

2,243

Class S

Class S Shares

127

397

686

1,511

Class I

Class I Shares

79

246

428

954

Class N

Class N Shares

78

243

422

942

Class T

Class T Shares

102

318

552

1,225

If Shares are not redeemed:

Expense Example, No Redemption Perkins Large Cap Value Fund Class A, C, S, I, N, T Shares (USD $)

Expense Example, No Redemption, By Year, Column [Text]

1 Year

3 Years

5 Years

10 Years

Class A

Class A Shares

684

913

1,161

1,871

Class C

Class C Shares

195

603

1,037

2,243

Class S

Class S Shares

127

397

686

1,511

Class I

Class I Shares

79

246

428

954

Class N

Class N Shares

78

243

422

942

Class T

Class T Shares

102

318

552

1,225

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 52% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objective by investing primarily in common stocks selected for their capital appreciation potential. The Fund primarily invests in the common stocks of large-sized companies whose stock prices the portfolio managers believe to be undervalued. The Fund invests, under normal circumstances, at least 80% of its net assets in equity securities of companies having, at the time of purchase, market capitalizations equal to or greater than the median market capitalization of companies included in the Russell 1000^® Value Index. The market capitalizations within the index will vary, but as of June 30, 2012, they ranged from approximately $1.3 billion to $400.1 billion, and the median market capitalization was $4.7 billion. The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets. The Fund may invest, under normal circumstances, up to 20% of its net assets in securities of companies having market capitalizations outside of the aforementioned market capitalization ranges. In addition, when the portfolio managers believe that market conditions are unfavorable for investing, or when they are otherwise unable to locate attractive investment opportunities, the Fund may invest up to 20% of its net assets in exchange-traded funds (“ETFs”), including commodity-related ETFs, cash or similar investments.

The Fund focuses on companies that have fallen out of favor with the market or that appear to be temporarily misunderstood by the investment community. The Fund’s portfolio managers generally look for companies with:

•   strong balance sheets and solid recurring free cash flows
•   attractive relative and absolute valuation ratios or that have underperformed recently
•   favorable reward to risk characteristics

The Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices, as substitutes for securities in which the Fund invests. The Fund may invest in derivative instruments (by taking long and/or short positions) for different purposes, including hedging (to offset risks associated with an investment, currency exposure, or market conditions) and to earn income and enhance returns. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s portfolio managers. When the Fund’s investments in cash or similar investments increase due to a lack of favorable investment opportunities or other extraordinary factors, the Fund may not participate in market advances or declines to the same extent that it would if the Fund had been fully invested.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio.

Exchange-Traded Funds Risk. The Fund may invest in ETFs which are typically open-end investment companies that are traded on a national securities exchange. ETFs typically incur fees, such as investment advisory fees and other operating expenses that are separate from those of the Fund, which will be indirectly paid by the Fund. As a result, the cost of investing in the Fund may be higher than the cost of investing directly in ETFs and may be higher than other mutual funds that invest directly in stocks and bonds. Further, the price movement of an ETF may fluctuate against the underlying securities or commodities it tracks and may result in a loss. Because the value of ETF shares depends on the demand in the market, the Fund may not be able to purchase or sell an ETF at the most optimal time, which could adversely affect the Fund’s performance.

The ETFs in which the Fund invests are subject to specific risks, depending on the investment strategy of the ETF. In turn, the Fund will be subject to substantially the same risks as those associated with direct exposure to the securities or commodities held by the ETF. Because the Fund may invest in a broad range of ETFs, such risks may include, but are not limited to, leverage risk, foreign exposure risk, and commodities risk.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class I Shares, Class A Shares, Class C Shares, and Class S Shares of the Fund commenced operations on July 6, 2009, after the reorganization of each corresponding class of shares of Janus Adviser Perkins Large Cap Value Fund (“JAD predecessor fund”) into each respective share class of the Fund. Class T Shares of the Fund commenced operations on July 6, 2009. Class N Shares of the Fund commenced operations on May 31, 2012.

• The performance shown for Class I Shares, Class A Shares, Class C Shares, and Class S Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund’s Class I Shares, Class A Shares, Class C Shares, and Class S Shares prior to the reorganization, calculated using the fees and expenses of each respective share class of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class N Shares reflects the performance of the Fund’s Class I Shares from July 6, 2009 to December 31, 2011, calculated using the fees and expenses of Class I Shares, net of any applicable fee and expense limitations or waivers. The performance shown for Class N Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund’s Class I Shares prior to the reorganization, calculated using the fees and expenses of Class I Shares of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class T Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund’s Class I Shares prior to the reorganization, calculated using the fees and expenses of Class T Shares, without the effect of any fee and expense limitations or waivers.

If Class T Shares of the Fund had been available during periods prior to July 6, 2009, or Class N Shares of the Fund had been available during periods prior to December 31, 2011, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class I Shares, Class A Shares, Class C Shares, Class S Shares, Class N Shares, and Class T Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Annual Total Returns for Class I Shares (calendar year-end)

Best Quarter:  Second Quarter 2009 15.40%     Worst Quarter:  Third Quarter 2011  -14.75%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 13.59%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Perkins Large Cap Value Fund Class A, C, S, I, N, T Shares

Column

Label

1 Year

Since Inception of Predecessor Fund

Inception Date

Class I Shares Return Before Taxes

Class I Shares

Return Before Taxes

(0.20%)

11.90%

Dec. 31, 2008

Class I Shares Return After Taxes on Distributions

Class I Shares

Return After Taxes on Distributions

(1.48%)

11.09%

Dec. 31, 2008

Class I Shares Return After Taxes on Distributions and Sale of Fund Shares

Class I Shares

Return After Taxes on Distributions and Sale of Fund Shares

^[1]

0.81%

10.04%

Dec. 31, 2008

Class A Shares Return Before Taxes

Class A Shares

Return Before Taxes

^[2]

(6.25%)

9.40%

Dec. 31, 2008

Class C Shares Return Before Taxes

Class C Shares

Return Before Taxes

^[3]

(2.20%)

10.74%

Dec. 31, 2008

Class S Shares Return Before Taxes

Class S Shares

Return Before Taxes

(0.72%)

11.36%

Dec. 31, 2008

Class N Shares Return Before Taxes

Class N Shares

Return Before Taxes

(0.20%)

11.90%

Dec. 31, 2008

Class T Shares Return Before Taxes

Class T Shares

Return Before Taxes

(0.41%)

11.49%

Dec. 31, 2008

Russell 1000 Value Index (reflects no deduction for expenses, fees, or taxes)

Russell 1000^® Value Index

0.39%

11.55%

Dec. 31, 2008

After-tax returns are calculated using distributions for the Fund’s Class I Shares for periods following July 6, 2009; and for the JAD predecessor fund’s Class I Shares for periods prior to July 6, 2009. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

[1] Other Expenses for Class N Shares are based on the estimated expenses that the Shares expect to incur during their initial fiscal period.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

XML

Janus Moderate Allocation Fund | Class D Shares

Fund summary

Janus Moderate Allocation Fund

INVESTMENT OBJECTIVE

Janus Moderate Allocation Fund seeks total return through growth of capital and income.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses		Janus Moderate Allocation Fund Class D Shares Class D
Operating Expenses Column [Text]		Class D
Management Fees		0.05%
Other Expenses	[1]	0.24%
Acquired Fund Fees and Expenses		0.69%
Total Annual Fund Operating Expenses		0.98%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses (including the operating expenses of the underlying funds) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Janus Moderate Allocation Fund Class D Shares	Class D Shares	100	312	542	1,201

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 18% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund seeks to achieve its investment objective by investing in other Janus mutual funds (“underlying funds”) that represent a variety of asset classes and investment styles. The Fund pursues this objective by investing in a diversified portfolio of underlying funds resulting in an allocation of the Fund’s investments that normally provides exposure of approximately 60% to stocks and 40% to bonds and money market securities. The target allocation and the allocation of the Fund’s assets among underlying funds are based on quantitative and qualitative analysis. Because it invests in other funds, the Fund is considered a “fund of funds.”

The Fund’s asset allocation is intended to diversify investments among stocks, bonds, and cash equivalents. The portfolio manager regularly reviews the allocation of Fund assets in the underlying funds and may modify the underlying funds’ weightings or substitute other underlying funds to emphasize and mitigate risk exposures that may arise as a result of the implementation of the allocations. An independent asset allocation service provides evaluations of asset allocations that the portfolio manager may use in implementing the allocations among the underlying funds. The portfolio manager continually monitors asset class allocations and periodically rebalances the Fund’s investments in the underlying funds. The portfolio manager may change the Fund’s asset class allocations, the underlying funds, an underlying fund’s asset category, or weightings among asset classes or underlying funds without prior shareholder notice.

The Fund will normally allocate approximately 60% of its investments to underlying funds that provide varying exposure to common stocks of large U.S.-based companies, small- to mid-capitalization companies, and international companies (including those with exposure to emerging markets); and approximately 40% of its investments to underlying bond funds and money market instruments. Refer to Appendix A in this Prospectus for a brief description of the investment strategies of each of the currently available underlying funds.

When market conditions dictate a more defensive strategy, the Fund or an underlying fund may temporarily hold cash or invest its assets in temporary investments. In that case, the Fund may take positions that are inconsistent with its investment objective. As a result, the Fund may not achieve its investment objective.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking growth of capital and income. Investments in a portfolio with common stock exposure tend to be more volatile than many other investment choices.

Main Risks Associated with the Fund
Allocation Risk. The Fund’s ability to achieve its investment objective depends largely upon the portfolio manager’s allocation of assets among the underlying funds and other securities, using the optimization process (a process that utilizes quantitative analysis of a number of factors, such as historical risk, performance, fund classifications, and the relationship among underlying funds) and the judgment of the portfolio manager. You could lose money on your investment in the Fund as a result of these allocations. The Fund will typically invest in a number of different underlying funds; however, to the extent that the Fund invests a significant portion of its assets in a single underlying fund, it will be more sensitive to the risks associated with that fund and any investments in which that fund concentrates.

Affiliated Fund Risk. Janus Capital has the authority to select and substitute underlying affiliated mutual funds. The fees paid to Janus Capital by some Janus mutual funds are generally higher than the fees paid to Janus Capital by the Fund or by other funds and share classes available for investment by the Fund. These conditions may create a conflict of interest when selecting underlying affiliated mutual funds and share classes for investment. Janus Capital, however, is a fiduciary to the Fund and its shareholders and is legally obligated to act in their best interest when selecting underlying affiliated mutual funds.

Main Risks Associated with the Underlying Funds and Securities
The biggest risk is that the underlying funds’ returns will vary, and you could lose money.

Market Risk. Approximately 60% of the Fund’s assets are allocated to equity investments through investments in underlying funds. The value of an underlying fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if a portfolio manager’s belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of an underlying fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Fixed-Income Securities Risk. Approximately 40% of the Fund’s assets are allocated to fixed-income securities through investments in underlying funds. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause an underlying fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which an underlying fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that an underlying fund’s portfolio manager would like or at the price that the portfolio manager believes the security is currently worth.

Foreign Exposure Risk. Certain underlying funds may have significant exposure to foreign markets as a result of their investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, an underlying fund’s returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. A market swing in one or more countries or regions where an underlying fund has invested a significant amount of its assets may have a greater effect on an underlying fund’s performance than it would in a more geographically diversified portfolio. An underlying fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Emerging Markets Risk. The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities involve a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. In addition, an underlying fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of an underlying fund’s investments. To the extent that an underlying fund invests a significant portion of its assets in the securities of issuers in or companies of a single country or region, it is more likely to be impacted by events or conditions affecting that country or region, which could have a negative impact on the Fund’s performance. Some of the risks of investing directly in foreign and emerging market securities may be reduced when an underlying fund invests indirectly in foreign securities through various other investment vehicles including derivatives, which also involve other risks.

Sovereign Debt Risk. An underlying fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Exchange-Traded Funds Risk. Certain underlying funds may purchase shares of exchange-traded funds (“ETFs”) to gain exposure to a particular portion of the market. ETFs are pooled investment vehicles, which may be managed or unmanaged, that generally seek to track the performance of a specific index. ETFs are traded on an exchange at market prices that may vary from the net asset value of their underlying investments. When an underlying fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF’s expenses. ETFs have certain inherent risks generally associated with investments in a portfolio of securities in which the ETF is invested, including the risk that the general level of stock prices may decline, thereby adversely affecting the value of each unit of the ETF. ETFs also involve the risk that an active trading market for an ETF’s shares may not develop or be maintained.

Exchange-Traded Notes Risk. Certain underlying funds may invest in exchange-traded notes (“ETNs”), which are debt securities whose returns are linked to a particular index. ETNs are typically linked to the performance of a commodities index that reflects the potential return on unleveraged investments in futures contracts of physical commodities, plus a specified rate of interest that could be earned on cash collateral. ETNs are subject to credit risk. The value of an ETN may vary and may be influenced by time to maturity, level of supply and demand for the ETN, volatility and lack of liquidity in underlying commodities markets, changes in the applicable interest rates, changes in the issuer’s credit rating, and economic, legal, political, or geographic events that affect the referenced commodity. When an underlying fund invests in ETNs it will bear its proportionate share of any fees and expenses borne by the ETN. There may be restrictions on an underlying fund’s right to redeem its investment in an ETN, which is meant to be held until maturity. An underlying fund’s decision to sell its ETN holdings may be limited by the availability of a secondary market.

Derivatives Risk. Certain underlying funds may invest in derivatives. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares, the predecessor share class. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses in effect during the periods shown, net of any applicable fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. Performance information for each underlying fund is available in its prospectus and/or the most recent annual or semiannual report. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Annual Total Returns for Class D Shares (calendar year-end)

Best Quarter: Second Quarter 2009 14.27%     Worst Quarter: Fourth Quarter 2008 −11.62%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 10.34%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Janus Moderate Allocation Fund Class D Shares	Column	Label		1 Year	5 Years	Since Inception	Inception Date
Class D Return Before Taxes	Class D Shares	Return Before Taxes		(2.55%)	3.74%	5.42%	Dec. 30, 2005
Class D Return After Taxes on Distributions	Class D Shares	Return After Taxes on Distributions		(3.27%)	2.84%	4.58%	Dec. 30, 2005
Class D Return After Taxes on Distributions and Sale of Fund Shares	Class D Shares	Return After Taxes on Distributions and Sale of Fund Shares	[1]	(1.53%)	2.74%	4.24%	Dec. 30, 2005
S&P 500 Index (reflects no deduction for expenses, fees, or taxes)		S&P 500® Index		2.11%	(0.25%)	2.26%	Dec. 30, 2005
Moderate Allocation Index (reflects no deduction for expenses, fees, or taxes)		Moderate Allocation Index		0.96%	2.43%	4.16%	Dec. 30, 2005

The Moderate Allocation Index is an internally-calculated, hypothetical combination of unmanaged indices that combines total returns from the Dow Jones Wilshire 5000 Index (40%), the Barclays U.S. Aggregate Bond Index (40%), the MSCI EAFE^® Index (18%), and the Morgan Stanley Capital International Emerging Markets Free Index^sm (2%).

After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; and for the Fund’s Class J Shares, the predecessor share class, for the periods prior to February 16, 2010. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

[1] Other Expenses are based on the estimated expenses that the Fund expects to incur.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

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Label

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Risk/Return:

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Registrant Name

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JANUS INVESTMENT FUND

Prospectus Date

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Oct. 26, 2012

Janus Short-Term Bond Fund | Class A, C, S, I, N, T Shares

Risk/Return:

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Risk/Return [Heading]

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Fund summary

Janus Short-Term Bond Fund

Objective [Heading]

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INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

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Janus Short-Term Bond Fund seeks as high a level of current income as is consistent with preservation of capital.

Expense [Heading]

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FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

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This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

Shareholder Fees Caption [Text]

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SHAREHOLDER FEES
(fees paid directly from your investment)

Operating Expenses Caption [Text]

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ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

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November 1, 2013

Portfolio Turnover [Heading]

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Portfolio Turnover:

Portfolio Turnover [Text Block]

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The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 93% of the average value of its portfolio.

Portfolio Turnover, Rate

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93.00%

Expense Breakpoint Discounts [Text]

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For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 51 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.

Expense Breakpoint, Minimum Investment Required [Amount]

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50,000

Expense Example [Heading]

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EXAMPLE:

Expense Example by Year [Heading]

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The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

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The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Expense Example by, Year, Caption [Text]

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If Shares are redeemed:

Expense Example, No Redemption, By Year, Caption [Text]

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If Shares are not redeemed:

Strategy [Heading]

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PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

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The Fund invests, under normal circumstances, at least 80% of its net assets in short- and intermediate-term securities such as corporate bonds or notes or government securities, including agency securities. The Fund may invest up to 35% of its net assets in high-yield/high risk bonds, also known as “junk bonds.” The Fund expects to maintain an average-weighted effective maturity of three years or less under normal circumstances. As of June 30, 2012, the Fund’s weighted average maturity was 2.4 years. The Fund may also invest in bank loans, mortgage-backed securities, asset-backed securities, and foreign debt securities (which may include investments in emerging markets). Due to the nature of securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

“Effective” maturity differs from actual maturity, which may be longer. In calculating the “effective” maturity the portfolio managers will estimate the effect of expected principal payments and call provisions on securities held in the portfolio. This gives the portfolio managers some additional flexibility in the securities they purchase, but all else being equal, could result in more volatility than if the Fund calculated an actual maturity target.

In addition, the Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. In particular, the Fund may use interest rate futures to manage portfolio risk. The Fund’s exposure to derivatives will vary. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

In addition to considering economic factors such as the effect of interest rates on the Fund’s investments, the portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income-producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

Risk [Heading]

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PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

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Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

Sovereign Debt Risk. The Fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However, investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Bank Loan Risk. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. Participation interests and assignments involve credit, interest rate, and liquidity risk. In addition, the bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. To the extent the Fund invests in foreign debt securities, such investments are sensitive to changes in interest rates. Additionally, investments in securities of foreign governments involve the risk that a foreign government may not be willing or able to pay interest or repay principal when due. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

High-Yield/High-Risk Bond Risk. High-yield/high-risk bonds may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

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Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

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An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

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PERFORMANCE INFORMATION

Performance Narrative [Text Block]

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The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares, the initial share class) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund commenced operations on July 6, 2009. Class N Shares of the Fund commenced operations on May 31, 2012.

• The performance shown for Class T Shares is calculated using the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class A Shares, Class C Shares, Class S Shares, and Class I Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers.
• The performance shown for Class N Shares for periods prior to December 31, 2011, reflects the performance of the Fund’s Class T Shares, calculated using the fees and expenses of Class T Shares, net of any applicable fee and expense limitations or waivers.

If Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund had been available during periods prior to July 6, 2009, or Class N Shares of the Fund had been available during periods prior to December 31, 2011, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class N Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Performance Information Illustrates Variability of Returns [Text]

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The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

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The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

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1-877-335-2687

Performance Availability Website Address [Text]

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janus.com/advisor/mutual-funds

Performance Past Does Not Indicate Future [Text]

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The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

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Annual Total Returns for Class T Shares (calendar year-end)

Bar Chart Does Not Reflect Sales Loads [Text]

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The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.

Bar Chart Closing [Text Block]

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Best Quarter:  Second Quarter 2009  3.18%          Worst Quarter:  Second Quarter 2008  −0.90%

Year to Date Return, Label

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The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 2.96%.

Performance Table Heading

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Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

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After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

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Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table One Class of after Tax Shown [Text]

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After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Explanation after Tax Higher

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If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

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After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares, the initial share class). After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Closing [Text Block]

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Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Janus Short-Term Bond Fund | Class A, C, S, I, N, T Shares | Class A

Risk/Return:

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Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class A

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

2.50%

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class A

Management Fees

rr_ManagementFeesOverAssets

0.55%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.14%

^[1]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.94%

^[2]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.14%

^[2]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.80%

^[2]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleYear01

344

3 Years

rr_ExpenseExampleYear03

542

5 Years

rr_ExpenseExampleYear05

757

10 Years

rr_ExpenseExampleYear10

1,376

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

344

3 Years

rr_ExpenseExampleNoRedemptionYear03

542

5 Years

rr_ExpenseExampleNoRedemptionYear05

757

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,376

Janus Short-Term Bond Fund | Class A, C, S, I, N, T Shares | Class C

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class C

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

1.00%

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class C

Management Fees

rr_ManagementFeesOverAssets

0.55%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

0.13%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.68%

^[2]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.13%

^[2]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.55%

^[2]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleYear01

271

3 Years

rr_ExpenseExampleYear03

530

5 Years

rr_ExpenseExampleYear05

913

10 Years

rr_ExpenseExampleYear10

1,987

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

171

3 Years

rr_ExpenseExampleNoRedemptionYear03

530

5 Years

rr_ExpenseExampleNoRedemptionYear05

913

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,987

Janus Short-Term Bond Fund | Class A, C, S, I, N, T Shares | Class S

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class S

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class S

Management Fees

rr_ManagementFeesOverAssets

0.55%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.29%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.09%

^[2]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.04%

^[2]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.05%

^[2]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleYear01

111

3 Years

rr_ExpenseExampleYear03

347

5 Years

rr_ExpenseExampleYear05

601

10 Years

rr_ExpenseExampleYear10

1,329

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

111

3 Years

rr_ExpenseExampleNoRedemptionYear03

347

5 Years

rr_ExpenseExampleNoRedemptionYear05

601

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,329

Janus Short-Term Bond Fund | Class A, C, S, I, N, T Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class I

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class I

Management Fees

rr_ManagementFeesOverAssets

0.55%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.09%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.64%

^[2]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.09%

^[2]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.55%

^[2]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleYear01

65

3 Years

rr_ExpenseExampleYear03

205

5 Years

rr_ExpenseExampleYear05

357

10 Years

rr_ExpenseExampleYear10

798

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

65

3 Years

rr_ExpenseExampleNoRedemptionYear03

205

5 Years

rr_ExpenseExampleNoRedemptionYear05

357

10 Years

rr_ExpenseExampleNoRedemptionYear10

798

Janus Short-Term Bond Fund | Class A, C, S, I, N, T Shares | Class N

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class N

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class N

Management Fees

rr_ManagementFeesOverAssets

0.55%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.05%

^[1]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.60%

^[2]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.05%

^[2]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.55%

^[2]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class N Shares

1 Year

rr_ExpenseExampleYear01

61

3 Years

rr_ExpenseExampleYear03

192

5 Years

rr_ExpenseExampleYear05

335

10 Years

rr_ExpenseExampleYear10

750

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class N Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

61

3 Years

rr_ExpenseExampleNoRedemptionYear03

192

5 Years

rr_ExpenseExampleNoRedemptionYear05

335

10 Years

rr_ExpenseExampleNoRedemptionYear10

750

Janus Short-Term Bond Fund | Class A, C, S, I, N, T Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class T

Management Fees

rr_ManagementFeesOverAssets

0.55%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.29%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.84%

^[2]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.04%

^[2]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.80%

^[2]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleYear01

86

3 Years

rr_ExpenseExampleYear03

268

5 Years

rr_ExpenseExampleYear05

466

10 Years

rr_ExpenseExampleYear10

1,037

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

86

3 Years

rr_ExpenseExampleNoRedemptionYear03

268

5 Years

rr_ExpenseExampleNoRedemptionYear05

466

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,037

2002

rr_AnnualReturn2002

3.57%

2003

rr_AnnualReturn2003

3.91%

2004

rr_AnnualReturn2004

1.96%

2005

rr_AnnualReturn2005

1.52%

2006

rr_AnnualReturn2006

4.21%

2007

rr_AnnualReturn2007

5.21%

2008

rr_AnnualReturn2008

4.63%

2009

rr_AnnualReturn2009

8.56%

2010

rr_AnnualReturn2010

3.37%

2011

rr_AnnualReturn2011

1.37%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

2.96%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

3.18%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Jun. 30, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(0.90%)

Janus Short-Term Bond Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class A

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class A Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[3]

1 Year

rr_AverageAnnualReturnYear01

(1.20%)

5 Years

rr_AverageAnnualReturnYear05

3.41%

10 Years

rr_AverageAnnualReturnYear10

2.98%

Since Inception

rr_AverageAnnualReturnSinceInception

3.98%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 01, 1992

Janus Short-Term Bond Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class C

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class C Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[4]

1 Year

rr_AverageAnnualReturnYear01

(0.03%)

5 Years

rr_AverageAnnualReturnYear05

3.84%

10 Years

rr_AverageAnnualReturnYear10

2.87%

Since Inception

rr_AverageAnnualReturnSinceInception

3.58%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 01, 1992

Janus Short-Term Bond Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class S

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class S Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

1.13%

5 Years

rr_AverageAnnualReturnYear05

4.09%

10 Years

rr_AverageAnnualReturnYear10

3.25%

Since Inception

rr_AverageAnnualReturnSinceInception

4.05%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 01, 1992

Janus Short-Term Bond Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

1.62%

5 Years

rr_AverageAnnualReturnYear05

4.59%

10 Years

rr_AverageAnnualReturnYear10

3.69%

Since Inception

rr_AverageAnnualReturnSinceInception

4.47%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 01, 1992

Janus Short-Term Bond Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class N

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class N Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

1.37%

5 Years

rr_AverageAnnualReturnYear05

4.60%

10 Years

rr_AverageAnnualReturnYear10

3.81%

Since Inception

rr_AverageAnnualReturnSinceInception

4.64%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 01, 1992

Janus Short-Term Bond Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

1.37%

5 Years

rr_AverageAnnualReturnYear05

4.60%

10 Years

rr_AverageAnnualReturnYear10

3.81%

Since Inception

rr_AverageAnnualReturnSinceInception

4.64%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 01, 1992

Janus Short-Term Bond Fund | Class A, C, S, I, N, T Shares | Return After Taxes on Distributions | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

0.58%

5 Years

rr_AverageAnnualReturnYear05

3.40%

10 Years

rr_AverageAnnualReturnYear10

2.62%

Since Inception

rr_AverageAnnualReturnSinceInception

2.92%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 01, 1992

Janus Short-Term Bond Fund | Class A, C, S, I, N, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[5]

1 Year

rr_AverageAnnualReturnYear01

0.93%

5 Years

rr_AverageAnnualReturnYear05

3.24%

10 Years

rr_AverageAnnualReturnYear10

2.56%

Since Inception

rr_AverageAnnualReturnSinceInception

2.90%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 01, 1992

Janus Short-Term Bond Fund | Class A, C, S, I, N, T Shares | Barclays 1-3 Year U.S. Government/Credit Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Barclays 1-3 Year U.S. Government/Credit Index

1 Year

rr_AverageAnnualReturnYear01

1.59%

5 Years

rr_AverageAnnualReturnYear05

3.99%

10 Years

rr_AverageAnnualReturnYear10

3.63%

Since Inception

rr_AverageAnnualReturnSinceInception

4.80%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 01, 1992

[1] Other Expenses for Class A Shares and Class N Shares are based on the estimated expenses that the Shares expect to incur.

[2] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, and Class S Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 0.55% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

[3] Calculated assuming maximum permitted sales loads.

[4] The one year return is calculated to include the contingent deferred sales charge.

[5] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Janus Real Return Fund | Class D Shares

Fund summary

Janus Real Return Fund
(formerly named Janus Real Return Allocation Fund)

INVESTMENT OBJECTIVE

Janus Real Return Fund seeks real return consistent with preservation of capital.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses		Janus Real Return Fund Class D Shares Class D
Operating Expenses Column [Text]		Class D
Management Fees		0.55%
Other Expenses	[1]	0.97%
Total Annual Fund Operating Expenses	[2]	1.52%
Fee Waiver	[2]	0.64%
Total Annual Fund Operating Expenses After Fee Waiver	[2]	0.88%

EXAMPLE:

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers or recoupments (if applicable) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Janus Real Return Fund Class D Shares Class D	Class D Shares	154	479	827	1,808

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 45% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objective by primarily investing in U.S. Treasury securities, short-duration high-yield/high-risk debt, commodity-linked investments, and equity securities. The Fund’s investments in U.S. Treasury securities may also include Treasury Inflation Protected Securities, also known as TIPS. As utilized by the Fund, each of these types of investments may be considered an “inflation-related investment,” which are those that may provide what is known as “real return,” or a rate of return above the rate of inflation over a full market cycle. Due to the nature of securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

The Fund may invest up to 90% of its net assets in short-duration high-yield/high-risk debt securities. The Fund’s investments in short-duration high-yield/high-risk securities include debt rated below investment grade, also known as “junk bonds.” Securities rated below investment grade may include their unrated equivalents or other high-yielding securities the portfolio managers believe offer attractive risk/return characteristics. The Fund may also invest in certain investment grade debt instruments, including corporate bonds, government bonds, municipal bonds, mortgage-backed securities, zero-coupon bonds, and agency securities. The Fund may invest in foreign debt securities.

To seek exposure to the commodities markets, the Fund may invest in commodity-linked investments such as commodity-related exchange-traded funds (“ETFs”), commodity index-linked swap agreements, commodity options and futures, and options on futures that provide exposure to the investment returns of the commodities markets. The Fund may also invest in other commodity-linked derivative instruments, such as commodity-linked notes (“structured notes”).

The Fund’s investments in equity securities may include common stock, preferred stock, and convertible securities, all of which may include exposure to foreign markets. The Fund may invest in companies of any market capitalization. The Fund’s equity investments may also include securities of real estate-related companies, including, but not limited to, real estate investment trusts (“REITs”) and similar REIT-like entities, such as foreign entities that have REIT characteristics.

The Fund may also invest in derivative instruments (by taking long and/or short positions) for various purposes, including hedging by shorting interest rate futures against long positions in TIPS, using inflation index swaps to hedge against unexpected changes in the rate of inflation, using interest rate swaps to hedge against changes in interest rates, to increase or decrease the Fund’s exposure to a particular market, to manage or adjust the risk profile of the Fund related to an investment, and to earn income and enhance returns. The Fund’s exposure to derivatives will vary, is not limited to those derivatives listed, and could be significant at times. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

The Fund may also use reverse repurchase agreements to generate income as part of its inflation-related strategies. Proceeds from reverse repurchase agreement transactions may be invested in other securities or instruments to attempt to increase the Fund’s investment return. The Fund may also invest in money market instruments, buy backs or dollar rolls, other securitized debt products, bank loans, various when-issued securities, exchange-traded notes, and other investment companies.

In addition to considering economic factors such as the rate of inflation and the effect of interest rates on the Fund’s investments, the portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

PRINCIPAL INVESTMENT RISKS

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Inflation-Related Investment Risk. Inflation index swaps and other inflation-linked securities are subject to inflation risk. A swap held long by the Fund can potentially lose value if the rate of inflation over the life of the swap is less than the fixed rate that the Fund agrees to pay at the initiation of the swap. Except for the Fund’s investments in U.S. Treasury securities, which are guaranteed as to principal by the U.S. Treasury, the inflation-adjusted principal value of inflation-linked securities repaid at maturity may be less than the original principal. Because of the inflation-linked adjustment feature, inflation-linked securities typically have lower yields than conventional fixed-rate securities. In the event of deflation, where prices decline over time, the principal and income of inflation-linked securities will likely decline, resulting in losses to the Fund.

High-Yield/High-Risk Bond Risk. The Fund may invest up to 90% of its net assets in higher-yielding/higher-risk bonds, also known as “junk” bonds. High-yield/high-risk bonds may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Commodity-Linked Investments Risk. The Fund may invest in various commodity-linked investments that provide exposure to the commodities markets. Such exposure may subject the Fund to greater volatility than investments in traditional securities. The value of a given commodity-linked derivative investment typically is based upon the price movements of a physical commodity (such as heating oil, livestock, or agricultural products), a commodity futures contract or commodity index, or some other readily measurable economic variable. The value of commodity-linked derivative instruments may therefore be affected by changes in overall market movements, volatility of the underlying benchmark, changes in interest rates, or other factors affecting a particular industry or commodity such as drought, floods, weather, livestock disease, embargoes, tariffs, and international economic, political, and regulatory developments.

Exchange-Traded Funds Risk. The Fund may invest in ETFs which are typically open-end investment companies that are traded on a national securities exchange. ETFs typically incur fees, such as investment advisory fees and other operating expenses that are separate from those of the Fund, which will be indirectly paid by the Fund. As a result, the cost of investing in the Fund may be higher than the cost of investing directly in ETFs and may be higher than other mutual funds that invest directly in stocks and bonds. Further, the price movement of an ETF may fluctuate against the underlying securities or commodities it tracks and may result in a loss. Because the value of ETF shares depends on the demand in the market, the Fund may not be able to purchase or sell an ETF at the most optimal time, which could adversely affect the Fund’s performance.

The ETFs in which the Fund invests are subject to specific risks, depending on the investment strategy of the ETF. In turn, the Fund will be subject to substantially the same risks as those associated with direct exposure to the securities or commodities held by the ETF. Because the Fund may invest in a broad range of ETFs, such risks may include, but are not limited to, leverage risk, foreign exposure risk, and commodities risk.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Sovereign Debt Risk. The Fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However, investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited.

Counterparty Risk. Certain derivative and “over-the-counter” instruments, such as swaps and forwards, are subject to the risk that the other party to a contract will not fulfill its contractual obligations.

Leverage Risk. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. In particular, certain commodity-linked investments may subject the Fund to leveraged market exposure to commodities. Leverage also occurs when the Fund increases its assets available for investment through borrowings, reverse repurchase agreements, or similar transactions. The Fund’s use of leverage can magnify the effect of any gains or losses, causing the Fund to be more volatile than if it had not been leveraged. There is no assurance that any leveraging strategy will be successful.

Reverse Repurchase Agreement Risk. Reverse repurchase agreements involve leverage risk, counterparty risk, and the risk that the value of securities that the Fund is obligated to repurchase under the agreement may decline below the repurchase price. When the Fund invests reverse repurchase transaction proceeds, the Fund is at risk for any fluctuations in the value of securities in which the proceeds are invested. To the extent the Fund uses reverse repurchase agreements, the value of an investment in the Fund may be more volatile, and such transactions may increase the Fund’s overall investment exposure. Additionally, interest expenses related to reverse repurchase transactions could exceed the rate of return on debt obligations and other investments held by the Fund, thereby reducing returns to shareholders.

Foreign Exposure Risk. The Fund normally has significant exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Growth Securities Risk. The Fund invests in companies after assessing their growth potential. Securities of companies perceived to be “growth” companies may be more volatile than other stocks and may involve special risks. If the portfolio managers’ perception of a company’s growth potential is not realized, the securities purchased may not perform as expected, reducing the Fund’s returns. In addition, because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “growth” stocks may perform differently from the market as a whole and other types of securities.

Real Estate Risk. An investment in the Fund may be subject to many of the same risks as a direct investment in real estate. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

Nondiversification Risk. The Fund is classified as nondiversified under the Investment Company Act of 1940, as amended. This gives the Fund’s portfolio managers more flexibility to hold larger positions in a smaller number of securities. As a result, an increase or decrease in the value of a single security held by the Fund may have a greater impact on the Fund’s net asset value and total return.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The Fund does not have a full calendar year of operations. Performance information for certain periods is included in the Fund’s first annual and/or semiannual report.

[1] Other Expenses are based on the estimated expenses that the Fund expects to incur.

[2] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding administrative services fees payable pursuant to the Transfer Agency Agreement, brokerage commissions, interest, dividends, taxes, acquired fund fees and expenses, and extraordinary expenses) to 0.76% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees. For a period of three years subsequent to the Fund's commencement of operations (May 13, 2011) or until the Fund's assets exceed the first breakpoint in the investment advisory fee schedule, whichever occurs first, Janus Capital may recover from the Fund fees and expenses previously waived or reimbursed, which could then be considered a deferral, if the Fund's expense ratio, including recovered expenses, falls below the expense limit.

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Janus Conservative Allocation Fund | Class A, C, S, I, T Shares

Fund summary

Janus Conservative Allocation Fund

INVESTMENT OBJECTIVE

Janus Conservative Allocation Fund seeks total return through a primary emphasis on income with a secondary emphasis on growth of capital.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 45 of the Fund’s Prospectus and in the “Purchases” section on page 63 of the Fund’s Statement of Additional Information.

SHAREHOLDER FEES
(fees paid directly from your investment)

Shareholder Fees Janus Conservative Allocation Fund Class A, C, S, I, T Shares	Class A	Class C	Class S	Class I	Class T
Shareholder Fees Column [Text]	Class A	Class C	Class S	Class I	Class T
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	5.75%	none	none	none	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	none	1.00%	none	none	none

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Janus Conservative Allocation Fund Class A, C, S, I, T Shares		Class A	Class C	Class S	Class I	Class T
Operating Expenses Column [Text]		Class A	Class C	Class S	Class I	Class T
Management Fees		0.05%	0.05%	0.05%	0.05%	0.05%
Distribution/Service (12b-1) Fees		0.25%	1.00%	0.25%	none	none
Other Expenses	[1]	0.18%	0.20%	0.33%	0.18%	0.33%
Acquired Fund Fees and Expenses		0.64%	0.64%	0.64%	0.64%	0.64%
Total Annual Fund Operating Expenses		1.11%	1.89%	1.27%	0.87%	1.02%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses (including the operating expenses of the underlying funds) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

If Shares are redeemed:

Expense Example Janus Conservative Allocation Fund Class A, C, S, I, T Shares (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	682	908	1,151	1,849
Class C	Class C Shares	292	594	1,021	2,212
Class S	Class S Shares	129	403	697	1,534
Class I	Class I Shares	89	278	482	1,073
Class T	Class T Shares	104	325	563	1,248

If Shares are not redeemed:

Expense Example, No Redemption Janus Conservative Allocation Fund Class A, C, S, I, T Shares (USD $)	Expense Example, No Redemption, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	682	908	1,151	1,849
Class C	Class C Shares	192	594	1,021	2,212
Class S	Class S Shares	129	403	697	1,534
Class I	Class I Shares	89	278	482	1,073
Class T	Class T Shares	104	325	563	1,248

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 10% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund seeks to achieve its investment objective by investing in other Janus mutual funds (“underlying funds”) that represent a variety of asset classes and investment styles. The Fund pursues this objective by investing in a diversified portfolio of underlying funds resulting in an allocation of the Fund’s investments that normally provides exposure of approximately 40% to stocks and 60% to bonds and money market securities. The target allocation and the allocation of the Fund’s assets among underlying funds are based on quantitative and qualitative analysis. Because it invests in other funds, the Fund is considered a “fund of funds.”

The Fund’s asset allocation is intended to diversify investments among stocks, bonds, and cash equivalents. The portfolio manager regularly reviews the allocation of Fund assets in the underlying funds and may modify the underlying funds’ weightings or substitute other underlying funds to emphasize and mitigate risk exposures that may arise as a result of the implementation of the allocations. An independent asset allocation service provides evaluations of asset allocations that the portfolio manager may use in implementing the allocations among the underlying funds. The portfolio manager continually monitors asset class allocations and periodically rebalances the Fund’s investments in the underlying funds. The portfolio manager may change the Fund’s asset class allocations, the underlying funds, an underlying fund’s asset category, or weightings among asset classes or underlying funds without prior shareholder notice.

The Fund will normally allocate approximately 60% of its investments to underlying bond funds and money market instruments; and approximately 40% of its investments to underlying funds that provide varying exposure to common stocks of large U.S.-based companies, small- to mid-capitalization companies, and international companies (including those with exposure to emerging markets). Refer to Appendix A in this Prospectus for a brief description of the investment strategies of each of the currently available underlying funds.

When market conditions dictate a more defensive strategy, the Fund or an underlying fund may temporarily hold cash or invest its assets in temporary investments. In that case, the Fund may take positions that are inconsistent with its investment objective. As a result, the Fund may not achieve its investment objective.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking income and, to a lesser extent, growth of capital. Investments in a portfolio with common stock exposure tend to be more volatile than many other investment choices.

Main Risks Associated with the Fund
Allocation Risk. The Fund’s ability to achieve its investment objective depends largely upon the portfolio manager’s allocation of assets among the underlying funds and other securities, using the optimization process (a process that utilizes quantitative analysis of a number of factors, such as historical risk, performance, fund classifications, and the relationship among underlying funds) and the judgment of the portfolio manager. You could lose money on your investment in the Fund as a result of these allocations. The Fund will typically invest in a number of different underlying funds; however, to the extent that the Fund invests a significant portion of its assets in a single underlying fund, it will be more sensitive to the risks associated with that fund and any investments in which that fund concentrates.

Affiliated Fund Risk. Janus Capital has the authority to select and substitute underlying affiliated mutual funds. The fees paid to Janus Capital by some Janus mutual funds are generally higher than the fees paid to Janus Capital by the Fund or by other funds and share classes available for investment by the Fund. These conditions may create a conflict of interest when selecting underlying affiliated mutual funds and share classes for investment. Janus Capital, however, is a fiduciary to the Fund and its shareholders and is legally obligated to act in their best interest when selecting underlying affiliated mutual funds.

Main Risks Associated with the Underlying Funds and Securities
The biggest risk is that the underlying funds’ returns will vary, and you could lose money.

Fixed-Income Securities Risk. Approximately 60% of the Fund’s assets are allocated to fixed-income securities through investments in underlying funds. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause an underlying fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which an underlying fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that an underlying fund’s portfolio manager would like or at the price that the portfolio manager believes the security is currently worth.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Market Risk. Approximately 40% of the Fund’s assets are allocated to equity investments through investments in underlying funds. The value of an underlying fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if a portfolio manager’s belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of an underlying fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Foreign Exposure Risk. Certain underlying funds may have significant exposure to foreign markets as a result of their investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, an underlying fund’s returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. A market swing in one or more countries or regions where an underlying fund has invested a significant amount of its assets may have a greater effect on an underlying fund’s performance than it would in a more geographically diversified portfolio. An underlying fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Emerging Markets Risk. The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities involve a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. In addition, an underlying fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of an underlying fund’s investments. To the extent that an underlying fund invests a significant portion of its assets in the securities of issuers in or companies of a single country or region, it is more likely to be impacted by events or conditions affecting that country or region, which could have a negative impact on the Fund’s performance. Some of the risks of investing directly in foreign and emerging market securities may be reduced when an underlying fund invests indirectly in foreign securities through various other investment vehicles including derivatives, which also involve other risks.

Sovereign Debt Risk. An underlying fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

Exchange-Traded Funds Risk. Certain underlying funds may purchase shares of exchange-traded funds (“ETFs”) to gain exposure to a particular portion of the market. ETFs are pooled investment vehicles, which may be managed or unmanaged, that generally seek to track the performance of a specific index. ETFs are traded on an exchange at market prices that may vary from the net asset value of their underlying investments. When an underlying fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF’s expenses. ETFs have certain inherent risks generally associated with investments in a portfolio of securities in which the ETF is invested, including the risk that the general level of stock prices may decline, thereby adversely affecting the value of each unit of the ETF. ETFs also involve the risk that an active trading market for an ETF’s shares may not develop or be maintained.

Exchange-Traded Notes Risk. Certain underlying funds may invest in exchange-traded notes (“ETNs”), which are debt securities whose returns are linked to a particular index. ETNs are typically linked to the performance of a commodities index that reflects the potential return on unleveraged investments in futures contracts of physical commodities, plus a specified rate of interest that could be earned on cash collateral. ETNs are subject to credit risk. The value of an ETN may vary and may be influenced by time to maturity, level of supply and demand for the ETN, volatility and lack of liquidity in underlying commodities markets, changes in the applicable interest rates, changes in the issuer’s credit rating, and economic, legal, political, or geographic events that affect the referenced commodity. When an underlying fund invests in ETNs it will bear its proportionate share of any fees and expenses borne by the ETN. There may be restrictions on an underlying fund’s right to redeem its investment in an ETN, which is meant to be held until maturity. An underlying fund’s decision to sell its ETN holdings may be limited by the availability of a secondary market.

Derivatives Risk. Certain underlying funds may invest in derivatives. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares, the initial share class) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund commenced operations on July 6, 2009.

• The performance shown for Class T Shares is calculated using the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class A Shares, Class C Shares, Class S Shares, and Class I Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers.

If Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund had been available during periods prior to July 6, 2009, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, and Class I Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. Performance information for each underlying fund is available in its prospectus and/or the most recent annual or semiannual report. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Annual Total Returns for Class T Shares (calendar year-end)

Best Quarter:  Second Quarter 2009  10.64%          Worst Quarter:  Third Quarter 2008   −6.58%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 9.25%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Janus Conservative Allocation Fund Class A, C, S, I, T Shares	Column	Label		1 Year	5 Years	Since Inception	Inception Date
Class T Shares Return Before Taxes	Class T Shares	Return Before Taxes		1.39%	5.07%	6.04%	Dec. 30, 2005
Class T Shares Return After Taxes on Distributions	Class T Shares	Return After Taxes on Distributions		0.44%	3.96%	5.00%	Dec. 30, 2005
Class T Shares Return After Taxes on Distributions and Sale of Fund Shares	Class T Shares	Return After Taxes on Distributions and Sale of Fund Shares	[1]	0.99%	3.73%	4.63%	Dec. 30, 2005
Class A Shares Return Before Taxes	Class A Shares	Return Before Taxes	[2]	(4.40%)	3.68%	4.83%	Dec. 30, 2005
Class C Shares Return Before Taxes	Class C Shares	Return Before Taxes	[3]	(0.28%)	4.15%	5.10%	Dec. 30, 2005
Class S Shares Return Before Taxes	Class S Shares	Return Before Taxes		1.13%	4.63%	5.59%	Dec. 30, 2005
Class I Shares Return Before Taxes	Class I Shares	Return Before Taxes		1.59%	5.07%	6.04%	Dec. 30, 2005
S&P 500 Index (reflects no deduction for expenses, fees, or taxes)		S&P 500® Index		2.11%	(0.25%)	2.26%	Dec. 30, 2005
Conservative Allocation Index (reflects no deduction for expenses, fees, or taxes)		Conservative Allocation Index		3.61%	3.89%	4.89%	Dec. 30, 2005

The Conservative Allocation Index is an internally-calculated, hypothetical combination of unmanaged indices that combines total returns from the Barclays U.S. Aggregate Bond Index (60%), the Dow Jones Wilshire 5000 Index (28%), and the Morgan Stanley Capital International Europe, Australasia, Far East Index (“MSCI EAFE^®”) Index (12%).

After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares, the initial share class). After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

[1] Other Expenses are based on the estimated expenses that the Fund expects to incur.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Perkins Small Cap Value Fund | Class L Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Perkins Small Cap Value Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Perkins Small Cap Value Fund seeks capital appreciation.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 62% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

62.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund pursues its investment objective by investing primarily in the common stocks of small companies whose stock prices are believed to be undervalued by the Fund’s portfolio managers. The Fund invests, under normal circumstances, at least 80% of its net assets in equity securities of small companies whose market capitalization, at the time of initial purchase, is less than the 12-month average of the maximum market capitalization for companies included in the Russell 2000^® Value Index. This average is updated monthly. The market capitalizations within the index will vary, but as of June 30, 2012, they ranged from approximately $85 million to $2.7 billion. The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets. The Fund may invest, under normal circumstances, up to 20% of its net assets in securities of companies having market capitalizations outside of the aforementioned market capitalization ranges. In addition, when the portfolio managers believe that market conditions are unfavorable for investing, or when they are otherwise unable to locate attractive investment opportunities, the Fund may invest up to 20% of its net assets in cash or similar investments.

The Fund’s securities selection focuses on companies that are out of favor with markets or have not yet been discovered by the broader investment community.

The Fund’s portfolio managers generally look for companies with:

• strong balance sheets and solid recurring free cash flows
• attractive relative and absolute valuation ratios or that have underperformed recently
• favorable reward to risk characteristics

The portfolio managers’ philosophy is to weigh a security’s downside risk before considering its upside potential, which may help provide an element of capital preservation.

Risk [Heading]

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PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

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The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s portfolio managers. When the Fund’s investments in cash or similar investments increase due to a lack of favorable investment opportunities or other extraordinary factors, the Fund may not participate in market advances or declines to the same extent that it would if the Fund had been fully invested.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Small-Sized Companies Risk. The Fund’s investments in securities issued by small-sized companies, which tend to be smaller, start-up companies offering emerging products or services, may involve greater risks than are customarily associated with larger, more established companies. Securities issued by small-sized companies tend to be more volatile and somewhat more speculative than securities issued by larger or more established companies and may underperform as compared to the securities of larger companies.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

The biggest risk is that the Fund’s returns will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

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PERFORMANCE INFORMATION

Performance Narrative [Text Block]

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The following information provides some indication of the risks of investing in the Fund by showing how the Fund's performance has varied over time. The performance shown for periods following April 21, 2003, reflects the fees and expenses of Class L Shares (formerly named Institutional Shares), net of any applicable fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class L Shares reflects the historical performance of Berger Small Cap Value Fund – Institutional Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Institutional Shares into the Fund's Class L Shares).

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund's average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund's performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund's average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-877-335-2687

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/advisor/mutual-funds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

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Annual Total Returns for Class L Shares (calendar year-end)

Bar Chart Closing [Text Block]

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Best Quarter:  Second Quarter 2009  23.27%          Worst Quarter:  Third Quarter 2002  −22.47%

Year to Date Return, Label

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The Fund's year-to-date return as of the calendar quarter ended September 30, 2012 was 6.38%.

Performance Table Heading

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Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

After-tax returns are calculated using distributions for the Fund's Class L Shares (formerly named Institutional Shares) for the periods following April 21, 2003 and for Berger Small Cap Value Fund – Institutional Shares for periods prior to April 21, 2003. If Class L Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Perkins Small Cap Value Fund | Class L Shares | Class L

Risk/Return:

rr_RiskReturnAbstract

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class L

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.75%

Other Expenses

rr_OtherExpensesOverAssets

0.27%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.02%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class L Shares

1 Year

rr_ExpenseExampleYear01

104

3 Years

rr_ExpenseExampleYear03

325

5 Years

rr_ExpenseExampleYear05

563

10 Years

rr_ExpenseExampleYear10

1,248

2002

rr_AnnualReturn2002

(15.33%)

2003

rr_AnnualReturn2003

37.18%

2004

rr_AnnualReturn2004

13.80%

2005

rr_AnnualReturn2005

9.14%

2006

rr_AnnualReturn2006

12.57%

2007

rr_AnnualReturn2007

3.21%

2008

rr_AnnualReturn2008

(21.63%)

2009

rr_AnnualReturn2009

36.91%

2010

rr_AnnualReturn2010

18.18%

2011

rr_AnnualReturn2011

(3.18%)

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

6.38%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

23.27%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2002

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(22.47%)

Perkins Small Cap Value Fund | Class L Shares | Return Before Taxes | Class L

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class L Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(3.18%)

5 Years

rr_AverageAnnualReturnYear05

4.85%

10 Years

rr_AverageAnnualReturnYear10

7.48%

Perkins Small Cap Value Fund | Class L Shares | Return After Taxes on Distributions | Class L

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class L Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

(5.68%)

5 Years

rr_AverageAnnualReturnYear05

3.09%

10 Years

rr_AverageAnnualReturnYear10

5.58%

Perkins Small Cap Value Fund | Class L Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class L

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class L Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[1]

1 Year

rr_AverageAnnualReturnYear01

(0.43%)

5 Years

rr_AverageAnnualReturnYear05

3.60%

10 Years

rr_AverageAnnualReturnYear10

5.93%

Perkins Small Cap Value Fund | Class L Shares | Russell 2000 Value Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Russell 2000^® Value Index

1 Year

rr_AverageAnnualReturnYear01

(5.50%)

5 Years

rr_AverageAnnualReturnYear05

(1.87%)

10 Years

rr_AverageAnnualReturnYear10

6.40%

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Janus High-Yield Fund | Class D Shares

Fund summary

Janus High-Yield Fund

INVESTMENT OBJECTIVES

Janus High-Yield Fund seeks to obtain high current income.

Capital appreciation is a secondary investment objective when consistent with its primary investment objective.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses	Janus High-Yield Fund Class D Shares Class D
Operating Expenses Column [Text]	Class D
Management Fees	0.57%
Other Expenses	0.19%
Total Annual Fund Operating Expenses	0.76%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Janus High-Yield Fund Class D Shares Class D	Class D Shares	78	243	422	942

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 61% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objectives by investing, under normal circumstances, at least 80% of its net assets in high-yield/high-risk securities rated below investment grade. Securities rated below investment grade may include their unrated equivalents or other high-yielding securities the portfolio managers believe offer attractive risk/return characteristics. The Fund may at times invest all of its assets in such securities. The Fund may also invest in bank loans, money market instruments, and foreign debt securities (which may include investments in emerging markets). Due to the nature of securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

In addition, the Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. In particular, the Fund may use interest rate futures to manage portfolio risk. The Fund’s exposure to derivatives will vary. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

In addition to considering economic factors such as the effect of interest rates on the Fund’s investments, the portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income-producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

PRINCIPAL INVESTMENT RISKS

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

High-Yield/High-Risk Bond Risk. The Fund may invest without limit in higher-yielding/higher-risk bonds, also known as “junk” bonds. High-yield/high-risk bonds may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Bank Loan Risk. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. Participation interests and assignments involve credit, interest rate, and liquidity risk. In addition, the bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. To the extent the Fund invests in foreign debt securities, such investments are sensitive to changes in interest rates. Additionally, investments in securities of foreign governments involve the risk that a foreign government may not be willing or able to pay interest or repay principal when due. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares, the predecessor share class. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses in effect during the periods shown, net of any applicable fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Annual Total Returns for Class D Shares (calendar year-end)

Best Quarter:  Second Quarter 2009  14.93%          Worst Quarter:  Fourth Quarter 2008  −12.96%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 10.80%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Janus High-Yield Fund Class D Shares	Column	Label		1 Year	5 Years	10 Years	Since Inception	Inception Date
Class D Return Before Taxes	Class D Shares	Return Before Taxes		3.32%	6.62%	7.44%	7.85%	Dec. 29, 1995
Class D Return After Taxes on Distributions	Class D Shares	Return After Taxes on Distributions		0.72%	3.40%	4.49%	4.55%	Dec. 29, 1995
Class D Return After Taxes on Distributions and Sale of Fund Shares	Class D Shares	Return After Taxes on Distributions and Sale of Fund Shares	[1]	2.15%	3.68%	4.58%	4.66%	Dec. 29, 1995
Barclays U.S. Corporate High-Yield Bond Index (reflects no deduction for expenses, fees, or taxes)		Barclays U.S. Corporate High-Yield Bond Index		4.98%	7.54%	8.85%	7.18%	Dec. 29, 1995

After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; and for the Fund’s Class J Shares, the predecessor share class, for the periods prior to February 16, 2010. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Janus Government Money Market Fund | Class T Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Janus Government Money Market Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVES

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Janus Government Money Market Fund seeks capital preservation and liquidity

Objective, Secondary [Text Block]

rr_ObjectiveSecondaryTextBlock

with current income as a secondary objective.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund pursues its investment objectives by investing exclusively in obligations issued and/or guaranteed as to principal and interest by the United States Government or by its agencies and instrumentalities, and repurchase agreements secured by such obligations. Although U.S. Government agencies and instrumentalities may be chartered or sponsored by Acts of Congress, their securities are not issued by, and may not be guaranteed by (i.e., backed by the full faith and credit of), the United States Treasury. Some government agency and instrumentality securities not backed by the full faith and credit of the United States are supported by the issuer’s ability to borrow from the U.S. Treasury, some are supported only by the credit of the issuer, and some are supported by the United States in some other way. For securities not backed by the full faith and credit of the U.S. Treasury, the Fund must look principally to the agency or instrumentality issuing or guaranteeing the securities for repayment and may not be able to assert a claim against the United States if the agency or instrumentality does not meet its commitment. The Fund’s investments in securities issued by U.S. Government agencies and instrumentalities may be significant.

The Fund will:

• invest in high quality, short-term money market instruments that present minimal credit risks, as determined by Janus Capital

• invest only in U.S. dollar-denominated instruments that have a remaining maturity of 397 days or less (as calculated pursuant to Rule 2a-7 under the Investment Company Act of 1940, as amended)

• maintain a dollar-weighted average portfolio maturity of 60 days or less and maintain a dollar-weighted average portfolio life (portfolio maturity measured without reference to any maturity shortening provisions of adjustable rate securities by reference to their interest rate reset dates) of 120 days or less

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

Market Risk. The Fund’s yield will vary as the short-term securities in its portfolio mature and the proceeds are reinvested in securities with different interest rates. For capital preservation and liquidity, the Fund may have a greater concentration in short-term securities including, but not limited to, investing up to all of its assets in overnight securities, which may result in a reduction of the Fund’s yield. Over time, the real value of the Fund’s yield may be eroded by inflation. Although the Fund invests only in high-quality, short-term money market instruments, there is a risk that the value of the securities it holds will fall as a result of changes in interest rates, an issuer’s actual or perceived creditworthiness, or an issuer’s ability to meet its obligations. The credit quality of the Fund’s holdings can change rapidly in certain market environments and any downgrade or default of a portfolio security could cause the Fund’s share price or yield to fall.

Collateral Risk. With respect to collateral received in repurchase transactions or other investments, the Fund may have significant exposure to government agencies not secured by the full faith and credit of the United States. Such exposure, depending on market conditions, could have a negative impact on the Fund, including minimizing the value of any collateral.

Money Market Risk. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund.

Risk Money Market Fund [Text]

rr_RiskMoneyMarketFund

Money Market Risk. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares, the initial share class) of the Fund commenced operations with the Fund’s inception. The performance shown for Class T Shares is calculated using the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table shows how the Fund’s returns over different periods average out. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-877-335-2687

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/advisor/mutual-funds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class T Shares (calendar year-end)

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Fourth Quarter 2006  1.21%          Worst Quarter:  Third Quarter 2011  0.00%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 0.00%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Money Market Seven Day Yield, Caption [Text]

rr_MoneyMarketSevenDayYieldCaption

The 7-day yield on December 31, 2011 was 0.00% for Janus Government Money Market Fund.

Money Market Seven Day Yield

rr_MoneyMarketSevenDayYield

0.00%

Janus Government Money Market Fund | Class T Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class T

Management Fees

rr_ManagementFeesOverAssets

0.20%

Other Expenses

rr_OtherExpensesOverAssets

0.51%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.71%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleYear01

73

3 Years

rr_ExpenseExampleYear03

227

5 Years

rr_ExpenseExampleYear05

395

10 Years

rr_ExpenseExampleYear10

883

2002

rr_AnnualReturn2002

1.33%

2003

rr_AnnualReturn2003

0.65%

2004

rr_AnnualReturn2004

0.85%

2005

rr_AnnualReturn2005

2.70%

2006

rr_AnnualReturn2006

4.52%

2007

rr_AnnualReturn2007

4.66%

2008

rr_AnnualReturn2008

1.83%

2009

rr_AnnualReturn2009

0.01%

2010

rr_AnnualReturn2010

0.02%

2011

rr_AnnualReturn2011

0.00%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

0.00%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Dec. 31, 2006

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

1.21%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

0.00%

Janus Government Money Market Fund | Class T Shares | Return Before Taxes | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

none

5 Years

rr_AverageAnnualReturnYear05

1.29%

10 Years

rr_AverageAnnualReturnYear10

1.64%

Since Inception

rr_AverageAnnualReturnSinceInception

2.99%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 14, 1995

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Janus Real Return Fund | Class A, C, S, I, T Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Janus Real Return Fund
(formerly named Janus Real Return Allocation Fund)

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Janus Real Return Fund seeks real return consistent with preservation of capital.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

SHAREHOLDER FEES
(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

November 1, 2013

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 45% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

45.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 31 of the Fund’s Prospectus and in the “Purchases” section on page 56 of the Fund’s Statement of Additional Information.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers or recoupments (if applicable) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

If Shares are redeemed:

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

If Shares are not redeemed:

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund pursues its investment objective by primarily investing in U.S. Treasury securities, short-duration high-yield/high-risk debt, commodity-linked investments, and equity securities. The Fund’s investments in U.S. Treasury securities may also include Treasury Inflation Protected Securities, also known as TIPS. As utilized by the Fund, each of these types of investments may be considered an “inflation-related investment,” which are those that may provide what is known as “real return,” or a rate of return above the rate of inflation over a full market cycle. Due to the nature of securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

The Fund may invest up to 90% of its net assets in short-duration high-yield/high-risk debt securities. The Fund’s investments in short-duration high-yield/high-risk securities include debt rated below investment grade, also known as “junk bonds.” Securities rated below investment grade may include their unrated equivalents or other high-yielding securities the portfolio managers believe offer attractive risk/return characteristics. The Fund may also invest in certain investment grade debt instruments, including corporate bonds, government bonds, municipal bonds, mortgage-backed securities, zero-coupon bonds, and agency securities. The Fund may invest in foreign debt securities.

To seek exposure to the commodities markets, the Fund may invest in commodity-linked investments such as commodity-related exchange-traded funds (“ETFs”), commodity index-linked swap agreements, commodity options and futures, and options on futures that provide exposure to the investment returns of the commodities markets. The Fund may also invest in other commodity-linked derivative instruments, such as commodity-linked notes (“structured notes”).

The Fund’s investments in equity securities may include common stock, preferred stock, and convertible securities, all of which may include exposure to foreign markets. The Fund may invest in companies of any market capitalization. The Fund’s equity investments may also include securities of real estate-related companies, including, but not limited to, real estate investment trusts (“REITs”) and similar REIT-like entities, such as foreign entities that have REIT characteristics.

The Fund may also invest in derivative instruments (by taking long and/or short positions) for various purposes, including hedging by shorting interest rate futures against long positions in TIPS, using inflation index swaps to hedge against unexpected changes in the rate of inflation, using interest rate swaps to hedge against changes in interest rates, to increase or decrease the Fund’s exposure to a particular market, to manage or adjust the risk profile of the Fund related to an investment, and to earn income and enhance returns. The Fund’s exposure to derivatives will vary, is not limited to those derivatives listed, and could be significant at times. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

The Fund may also use reverse repurchase agreements to generate income as part of its inflation-related strategies. Proceeds from reverse repurchase agreement transactions may be invested in other securities or instruments to attempt to increase the Fund’s investment return. The Fund may also invest in money market instruments, buy backs or dollar rolls, other securitized debt products, bank loans, various when-issued securities, exchange-traded notes, and other investment companies.

In addition to considering economic factors such as the rate of inflation and the effect of interest rates on the Fund’s investments, the portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Inflation-Related Investment Risk. Inflation index swaps and other inflation-linked securities are subject to inflation risk. A swap held long by the Fund can potentially lose value if the rate of inflation over the life of the swap is less than the fixed rate that the Fund agrees to pay at the initiation of the swap. Except for the Fund’s investments in U.S. Treasury securities, which are guaranteed as to principal by the U.S. Treasury, the inflation-adjusted principal value of inflation-linked securities repaid at maturity may be less than the original principal. Because of the inflation-linked adjustment feature, inflation-linked securities typically have lower yields than conventional fixed-rate securities. In the event of deflation, where prices decline over time, the principal and income of inflation-linked securities will likely decline, resulting in losses to the Fund.

High-Yield/High-Risk Bond Risk. The Fund may invest up to 90% of its net assets in higher-yielding/higher-risk bonds, also known as “junk” bonds. High-yield/high-risk bonds may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Commodity-Linked Investments Risk. The Fund may invest in various commodity-linked investments that provide exposure to the commodities markets. Such exposure may subject the Fund to greater volatility than investments in traditional securities. The value of a given commodity-linked derivative investment typically is based upon the price movements of a physical commodity (such as heating oil, livestock, or agricultural products), a commodity futures contract or commodity index, or some other readily measurable economic variable. The value of commodity-linked derivative instruments may therefore be affected by changes in overall market movements, volatility of the underlying benchmark, changes in interest rates, or other factors affecting a particular industry or commodity such as drought, floods, weather, livestock disease, embargoes, tariffs, and international economic, political, and regulatory developments.

Exchange-Traded Funds Risk. The Fund may invest in ETFs which are typically open-end investment companies that are traded on a national securities exchange. ETFs typically incur fees, such as investment advisory fees and other operating expenses that are separate from those of the Fund, which will be indirectly paid by the Fund. As a result, the cost of investing in the Fund may be higher than the cost of investing directly in ETFs and may be higher than other mutual funds that invest directly in stocks and bonds. Further, the price movement of an ETF may fluctuate against the underlying securities or commodities it tracks and may result in a loss. Because the value of ETF shares depends on the demand in the market, the Fund may not be able to purchase or sell an ETF at the most optimal time, which could adversely affect the Fund’s performance.

The ETFs in which the Fund invests are subject to specific risks, depending on the investment strategy of the ETF. In turn, the Fund will be subject to substantially the same risks as those associated with direct exposure to the securities or commodities held by the ETF. Because the Fund may invest in a broad range of ETFs, such risks may include, but are not limited to, leverage risk, foreign exposure risk, and commodities risk.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Sovereign Debt Risk. The Fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However, investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited.

Counterparty Risk. Certain derivative and “over-the-counter” instruments, such as swaps and forwards, are subject to the risk that the other party to a contract will not fulfill its contractual obligations.

Leverage Risk. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. In particular, certain commodity-linked investments may subject the Fund to leveraged market exposure to commodities. Leverage also occurs when the Fund increases its assets available for investment through borrowings, reverse repurchase agreements, or similar transactions. The Fund’s use of leverage can magnify the effect of any gains or losses, causing the Fund to be more volatile than if it had not been leveraged. There is no assurance that any leveraging strategy will be successful.

Reverse Repurchase Agreement Risk. Reverse repurchase agreements involve leverage risk, counterparty risk, and the risk that the value of securities that the Fund is obligated to repurchase under the agreement may decline below the repurchase price. When the Fund invests reverse repurchase transaction proceeds, the Fund is at risk for any fluctuations in the value of securities in which the proceeds are invested. To the extent the Fund uses reverse repurchase agreements, the value of an investment in the Fund may be more volatile, and such transactions may increase the Fund’s overall investment exposure. Additionally, interest expenses related to reverse repurchase transactions could exceed the rate of return on debt obligations and other investments held by the Fund, thereby reducing returns to shareholders.

Foreign Exposure Risk. The Fund normally has significant exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Growth Securities Risk. The Fund invests in companies after assessing their growth potential. Securities of companies perceived to be “growth” companies may be more volatile than other stocks and may involve special risks. If the portfolio managers’ perception of a company’s growth potential is not realized, the securities purchased may not perform as expected, reducing the Fund’s returns. In addition, because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “growth” stocks may perform differently from the market as a whole and other types of securities.

Real Estate Risk. An investment in the Fund may be subject to many of the same risks as a direct investment in real estate. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

Nondiversification Risk. The Fund is classified as nondiversified under the Investment Company Act of 1940, as amended. This gives the Fund’s portfolio managers more flexibility to hold larger positions in a smaller number of securities. As a result, an increase or decrease in the value of a single security held by the Fund may have a greater impact on the Fund’s net asset value and total return.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Risk Nondiversified Status [Text]

rr_RiskNondiversifiedStatus

Nondiversification Risk. The Fund is classified as nondiversified under the Investment Company Act of 1940, as amended. This gives the Fund’s portfolio managers more flexibility to hold larger positions in a smaller number of securities. As a result, an increase or decrease in the value of a single security held by the Fund may have a greater impact on the Fund’s net asset value and total return.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The Fund does not have a full calendar year of operations. Performance information for certain periods is included in the Fund’s first annual and/or semiannual report.

Performance One Year or Less [Text]

rr_PerformanceOneYearOrLess

The Fund does not have a full calendar year of operations.

Janus Real Return Fund | Class A, C, S, I, T Shares | Class A

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class A

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

4.75%

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class A

Management Fees

rr_ManagementFeesOverAssets

0.55%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.70%

^[1]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.50%

^[2]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.49%

^[2]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.01%

^[2]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleYear01

620

3 Years

rr_ExpenseExampleYear03

926

5 Years

rr_ExpenseExampleYear05

1,253

10 Years

rr_ExpenseExampleYear10

2,177

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

620

3 Years

rr_ExpenseExampleNoRedemptionYear03

926

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,253

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,177

Janus Real Return Fund | Class A, C, S, I, T Shares | Class C

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class C

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

1.00%

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class C

Management Fees

rr_ManagementFeesOverAssets

0.55%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

0.69%

^[1]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

2.24%

^[2]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.48%

^[2]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.76%

^[2]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleYear01

327

3 Years

rr_ExpenseExampleYear03

700

5 Years

rr_ExpenseExampleYear05

1,199

10 Years

rr_ExpenseExampleYear10

2,573

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

227

3 Years

rr_ExpenseExampleNoRedemptionYear03

700

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,199

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,573

Janus Real Return Fund | Class A, C, S, I, T Shares | Class S

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class S

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class S

Management Fees

rr_ManagementFeesOverAssets

0.55%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.94%

^[1]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.74%

^[2]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.48%

^[2]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.26%

^[2]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleYear01

177

3 Years

rr_ExpenseExampleYear03

547

5 Years

rr_ExpenseExampleYear05

943

10 Years

rr_ExpenseExampleYear10

2,049

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

177

3 Years

rr_ExpenseExampleNoRedemptionYear03

547

5 Years

rr_ExpenseExampleNoRedemptionYear05

943

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,049

Janus Real Return Fund | Class A, C, S, I, T Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class I

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class I

Management Fees

rr_ManagementFeesOverAssets

0.55%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.69%

^[1]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.24%

^[2]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.48%

^[2]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.76%

^[2]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleYear01

126

3 Years

rr_ExpenseExampleYear03

393

5 Years

rr_ExpenseExampleYear05

680

10 Years

rr_ExpenseExampleYear10

1,498

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

126

3 Years

rr_ExpenseExampleNoRedemptionYear03

393

5 Years

rr_ExpenseExampleNoRedemptionYear05

680

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,498

Janus Real Return Fund | Class A, C, S, I, T Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class T

Management Fees

rr_ManagementFeesOverAssets

0.55%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.94%

^[1]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.49%

^[2]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.48%

^[2]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.01%

^[2]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleYear01

151

3 Years

rr_ExpenseExampleYear03

470

5 Years

rr_ExpenseExampleYear05

812

10 Years

rr_ExpenseExampleYear10

1,777

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

151

3 Years

rr_ExpenseExampleNoRedemptionYear03

470

5 Years

rr_ExpenseExampleNoRedemptionYear05

812

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,777

[1] Other Expenses are based on the estimated expenses that the Fund expects to incur.

[2] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, and Class S Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 0.76% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees. For a period of three years subsequent to the Fund's commencement of operations (May 13, 2011) or until the Fund's assets exceed the first breakpoint in the investment advisory fee schedule, whichever occurs first, Janus Capital may recover from the Fund fees and expenses previously waived or reimbursed, which could then be considered a deferral, if the Fund's expense ratio, including recovered expenses, falls below the expense limit.

XML

Perkins Small Cap Value Fund | Class D Shares

Fund summary

Perkins Small Cap Value Fund

INVESTMENT OBJECTIVE

Perkins Small Cap Value Fund seeks capital appreciation.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses	Perkins Small Cap Value Fund Class D Shares Class D
Operating Expenses Column [Text]	Class D
Management Fees (may adjust up or down)	0.75%
Other Expenses	0.20%
Total Annual Fund Operating Expenses	0.95%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Perkins Small Cap Value Fund Class D Shares Class D	Class D Shares	97	303	525	1,166

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 62% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objective by investing primarily in the common stocks of small companies whose stock prices are believed to be undervalued by the Fund’s portfolio managers. The Fund invests, under normal circumstances, at least 80% of its net assets in equity securities of small companies whose market capitalization, at the time of initial purchase, is less than the 12-month average of the maximum market capitalization for companies included in the Russell 2000^® Value Index. This average is updated monthly. The market capitalizations within the index will vary, but as of June 30, 2012, they ranged from approximately $85 million to $2.7 billion. The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets. The Fund may invest, under normal circumstances, up to 20% of its net assets in securities of companies having market capitalizations outside of the aforementioned market capitalization ranges. In addition, when the portfolio managers believe that market conditions are unfavorable for investing, or when they are otherwise unable to locate attractive investment opportunities, the Fund may invest up to 20% of its net assets in cash or similar investments.

The Fund’s securities selection focuses on companies that are out of favor with markets or have not yet been discovered by the broader investment community.

The Fund’s portfolio managers generally look for companies with:

• strong balance sheets and solid recurring free cash flows
• attractive relative and absolute valuation ratios or that have underperformed recently
• favorable reward to risk characteristics

The portfolio managers’ philosophy is to weigh a security’s downside risk before considering its upside potential, which may help provide an element of capital preservation.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s portfolio managers. When the Fund’s investments in cash or similar investments increase due to a lack of favorable investment opportunities or other extraordinary factors, the Fund may not participate in market advances or declines to the same extent that it would if the Fund had been fully invested.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Small-Sized Companies Risk. The Fund’s investments in securities issued by small-sized companies, which tend to be smaller, start-up companies offering emerging products or services, may involve greater risks than are customarily associated with larger, more established companies. Securities issued by small-sized companies tend to be more volatile and somewhat more speculative than securities issued by larger or more established companies and may underperform as compared to the securities of larger companies.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares (formerly named Investor Shares). For the periods prior to April 21, 2003, the performance shown for Class D Shares reflects the historical performance of Berger Small Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Investor Shares into the Fund’s Class J Shares). If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Annual Total Returns for Class D Shares (calendar year-end)

Best Quarter:  Second Quarter 2009  23.04%          Worst Quarter:  Third Quarter 2002  −22.57%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 6.28%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Perkins Small Cap Value Fund Class D Shares	Column	Label		1 Year	5 Years	10 Years
Class D Return Before Taxes	Class D Shares	Return Before Taxes		(3.33%)	4.64%	7.25%
Class D Return After Taxes on Distributions	Class D Shares	Return After Taxes on Distributions		(5.81%)	2.91%	5.38%
Class D Return After Taxes on Distributions and Sale of Fund Shares	Class D Shares	Return After Taxes on Distributions and Sale of Fund Shares	[1]	(0.51%)	3.44%	5.75%
Russell 2000 Value Index (reflects no deduction for expenses, fees, or taxes)		Russell 2000® Value Index		(5.50%)	(1.87%)	6.40%

After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; for the Fund’s Class J Shares (formerly named Investor Shares) for the period April 21, 2003 to February 16, 2010; and for Berger Small Cap Value Fund – Investor Shares for periods prior to April 21, 2003. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Perkins Large Cap Value Fund | Class D Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Perkins Large Cap Value Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Perkins Large Cap Value Fund seeks capital appreciation.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 52% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

52.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund pursues its investment objective by investing primarily in common stocks selected for their capital appreciation potential. The Fund primarily invests in the common stocks of large-sized companies whose stock prices the portfolio managers believe to be undervalued. The Fund invests, under normal circumstances, at least 80% of its net assets in equity securities of companies having, at the time of purchase, market capitalizations equal to or greater than the median market capitalization of companies included in the Russell 1000^® Value Index. The market capitalizations within the index will vary, but as of June 30, 2012, they ranged from approximately $1.3 billion to $400.1 billion, and the median market capitalization was $4.7 billion. The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets. The Fund may invest, under normal circumstances, up to 20% of its net assets in securities of companies having market capitalizations outside of the aforementioned market capitalization ranges. In addition, when the portfolio managers believe that market conditions are unfavorable for investing, or when they are otherwise unable to locate attractive investment opportunities, the Fund may invest up to 20% of its net assets in exchange-traded funds (“ETFs”), including commodity-related ETFs, cash or similar investments.

The Fund focuses on companies that have fallen out of favor with the market or that appear to be temporarily misunderstood by the investment community. The Fund’s portfolio managers generally look for companies with:

• strong balance sheets and solid recurring free cash flows
• attractive relative and absolute valuation ratios or that have underperformed recently
• favorable reward to risk characteristics

The Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices, as substitutes for securities in which the Fund invests. The Fund may invest in derivative instruments (by taking long and/or short positions) for different purposes, including hedging (to offset risks associated with an investment, currency exposure, or market conditions) and to earn income and enhance returns. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s portfolio managers. When the Fund’s investments in cash or similar investments increase due to a lack of favorable investment opportunities or other extraordinary factors, the Fund may not participate in market advances or declines to the same extent that it would if the Fund had been fully invested.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio.

Exchange-Traded Funds Risk. The Fund may invest in ETFs which are typically open-end investment companies that are traded on a national securities exchange. ETFs typically incur fees, such as investment advisory fees and other operating expenses that are separate from those of the Fund, which will be indirectly paid by the Fund. As a result, the cost of investing in the Fund may be higher than the cost of investing directly in ETFs and may be higher than other mutual funds that invest directly in stocks and bonds. Further, the price movement of an ETF may fluctuate against the underlying securities or commodities it tracks and may result in a loss. Because the value of ETF shares depends on the demand in the market, the Fund may not be able to purchase or sell an ETF at the most optimal time, which could adversely affect the Fund’s performance.

The ETFs in which the Fund invests are subject to specific risks, depending on the investment strategy of the ETF. In turn, the Fund will be subject to substantially the same risks as those associated with direct exposure to the securities or commodities held by the ETF. Because the Fund may invest in a broad range of ETFs, such risks may include, but are not limited to, leverage risk, foreign exposure risk, and commodities risk.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

The biggest risk is that the Fund's returns will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010. The performance shown for Class D Shares for the period July 6, 2009 to February 16, 2010, reflects the performance of the Fund’s Class I Shares, calculated using the fees and expenses of Class D Shares, without the effect of any fee and expense limitations or waivers. Performance shown for the period prior to July 6, 2009, reflects the historical performance of the Janus Adviser Perkins Large Cap Value Fund’s (“JAD predecessor fund”) Class I Shares prior to the reorganization of Class I Shares of the JAD predecessor fund into Class I Shares of the Fund, calculated using the fees and expenses of Class D Shares, without the effect of any fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund's performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund's average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-800-525-3713

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/allfunds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class D Shares (calendar year-end)

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Second Quarter 2009  15.02%          Worst Quarter:  Third Quarter 2011  −14.77%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 13.38%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; for the Fund’s Class I Shares for the period following July 6, 2009; and for the JAD predecessor fund’s Class I Shares for the period prior to July 6, 2009. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Perkins Large Cap Value Fund | Class D Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class D

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.62%

Other Expenses

rr_OtherExpensesOverAssets

0.33%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.95%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class D Shares

1 Year

rr_ExpenseExampleYear01

97

3 Years

rr_ExpenseExampleYear03

303

5 Years

rr_ExpenseExampleYear05

525

10 Years

rr_ExpenseExampleYear10

1,166

2009

rr_AnnualReturn2009

23.61%

2010

rr_AnnualReturn2010

11.94%

2011

rr_AnnualReturn2011

(0.37%)

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

13.38%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

15.02%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(14.77%)

Perkins Large Cap Value Fund | Class D Shares | Return Before Taxes | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(0.37%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

11.29%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class D Shares | Return After Taxes on Distributions | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

(1.63%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

10.50%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class D Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[1]

1 Year

rr_AverageAnnualReturnYear01

0.69%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

9.52%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class D Shares | Russell 1000 Value Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Russell 1000^® Value Index

1 Year

rr_AverageAnnualReturnYear01

0.39%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

11.55%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Janus Flexible Bond Fund | Class A, C, S, I, N, R, T Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Janus Flexible Bond Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Janus Flexible Bond Fund seeks to obtain maximum total return, consistent with preservation of capital.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

SHAREHOLDER FEES
(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 126% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

126.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 51 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

If Shares are redeemed:

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

If Shares are not redeemed:

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund pursues its investment objective by primarily investing, under normal circumstances, at least 80% of its net assets in bonds. Bonds include, but are not limited to, government notes and bonds, corporate bonds, convertible bonds, mortgage-backed securities, and zero-coupon bonds. The Fund will invest at least 65% of its assets in investment grade debt securities. As of June 30, 2012, the Fund’s weighted average maturity was 7.9 years. The Fund will limit its investment in high-yield/high-risk bonds, also known as “junk bonds,” to 35% or less of its net assets. The Fund generates total return from a combination of current income and capital appreciation, but income is usually the dominant portion. The Fund may also invest in asset-backed securities, money market instruments, bank loans, and foreign debt securities (which may include investments in emerging markets). Due to the nature of the securities in which the Fund invests, it may have relatively high portfolio turnover compared to other Funds.

In addition, the Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. In particular, the Fund may use interest rate futures to manage portfolio risk. The Fund’s exposure to derivatives will vary. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

In addition to considering economic factors such as the effect of interest rates on the Fund’s investments, the portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income-producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Sovereign Debt Risk. The Fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However, investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

High-Yield/High-Risk Bond Risk. High-yield/high-risk bonds may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Bank Loan Risk. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. Participation interests and assignments involve credit, interest rate, and liquidity risk. In addition, the bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. To the extent the Fund invests in foreign debt securities, such investments are sensitive to changes in interest rates. Additionally, investments in securities of foreign governments involve the risk that a foreign government may not be willing or able to pay interest or repay principal when due. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares, the initial share class) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class R Shares of the Fund commenced operations on July 6, 2009. Class N Shares of the Fund commenced operations on May 31, 2012.

• The performance shown for Class T Shares is calculated using the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class A Shares, Class C Shares, Class S Shares, and Class R Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers.
• The performance shown for Class I Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class N Shares for periods prior to December 31, 2011, reflects the performance of the Fund’s Class T Shares, calculated using the fees and expenses of Class T Shares, net of any applicable fee and expense limitations or waivers.

If Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class R Shares of the Fund had been available during periods prior to July 6, 2009, or Class N Shares of the Fund had been available during periods prior to December 31, 2011, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, Class I Shares, Class N Shares, and Class R Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-877-335-2687

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/advisor/mutual-funds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class T Shares (calendar year-end)

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Third Quarter 2009  5.58%          Worst Quarter:  Second Quarter 2004  −2.99%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 7.11%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares, the initial share class). After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Janus Flexible Bond Fund | Class A, C, S, I, N, R, T Shares | Class A

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class A

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

4.75%

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class A

Management Fees

rr_ManagementFeesOverAssets

0.41%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.11%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.77%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleYear01

550

3 Years

rr_ExpenseExampleYear03

709

5 Years

rr_ExpenseExampleYear05

883

10 Years

rr_ExpenseExampleYear10

1,384

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

550

3 Years

rr_ExpenseExampleNoRedemptionYear03

709

5 Years

rr_ExpenseExampleNoRedemptionYear05

883

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,384

Janus Flexible Bond Fund | Class A, C, S, I, N, R, T Shares | Class C

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class C

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

1.00%

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class C

Management Fees

rr_ManagementFeesOverAssets

0.41%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

0.14%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.55%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleYear01

258

3 Years

rr_ExpenseExampleYear03

490

5 Years

rr_ExpenseExampleYear05

845

10 Years

rr_ExpenseExampleYear10

1,845

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

158

3 Years

rr_ExpenseExampleNoRedemptionYear03

490

5 Years

rr_ExpenseExampleNoRedemptionYear05

845

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,845

Janus Flexible Bond Fund | Class A, C, S, I, N, R, T Shares | Class S

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class S

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class S

Management Fees

rr_ManagementFeesOverAssets

0.41%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.29%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.95%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleYear01

97

3 Years

rr_ExpenseExampleYear03

303

5 Years

rr_ExpenseExampleYear05

525

10 Years

rr_ExpenseExampleYear10

1,166

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

97

3 Years

rr_ExpenseExampleNoRedemptionYear03

303

5 Years

rr_ExpenseExampleNoRedemptionYear05

525

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,166

Janus Flexible Bond Fund | Class A, C, S, I, N, R, T Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class I

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class I

Management Fees

rr_ManagementFeesOverAssets

0.41%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.14%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.55%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleYear01

56

3 Years

rr_ExpenseExampleYear03

176

5 Years

rr_ExpenseExampleYear05

307

10 Years

rr_ExpenseExampleYear10

689

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

56

3 Years

rr_ExpenseExampleNoRedemptionYear03

176

5 Years

rr_ExpenseExampleNoRedemptionYear05

307

10 Years

rr_ExpenseExampleNoRedemptionYear10

689

Janus Flexible Bond Fund | Class A, C, S, I, N, R, T Shares | Class N

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class N

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class N

Management Fees

rr_ManagementFeesOverAssets

0.41%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.05%

^[1]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.46%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class N Shares

1 Year

rr_ExpenseExampleYear01

47

3 Years

rr_ExpenseExampleYear03

148

5 Years

rr_ExpenseExampleYear05

258

10 Years

rr_ExpenseExampleYear10

579

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class N Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

47

3 Years

rr_ExpenseExampleNoRedemptionYear03

148

5 Years

rr_ExpenseExampleNoRedemptionYear05

258

10 Years

rr_ExpenseExampleNoRedemptionYear10

579

Janus Flexible Bond Fund | Class A, C, S, I, N, R, T Shares | Class R

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class R

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class R

Management Fees

rr_ManagementFeesOverAssets

0.41%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.50%

Other Expenses

rr_OtherExpensesOverAssets

0.29%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.20%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class R Shares

1 Year

rr_ExpenseExampleYear01

122

3 Years

rr_ExpenseExampleYear03

381

5 Years

rr_ExpenseExampleYear05

660

10 Years

rr_ExpenseExampleYear10

1,455

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class R Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

122

3 Years

rr_ExpenseExampleNoRedemptionYear03

381

5 Years

rr_ExpenseExampleNoRedemptionYear05

660

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,455

Janus Flexible Bond Fund | Class A, C, S, I, N, R, T Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class T

Management Fees

rr_ManagementFeesOverAssets

0.41%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.29%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.70%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleYear01

72

3 Years

rr_ExpenseExampleYear03

224

5 Years

rr_ExpenseExampleYear05

390

10 Years

rr_ExpenseExampleYear10

871

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

72

3 Years

rr_ExpenseExampleNoRedemptionYear03

224

5 Years

rr_ExpenseExampleNoRedemptionYear05

390

10 Years

rr_ExpenseExampleNoRedemptionYear10

871

2002

rr_AnnualReturn2002

9.93%

2003

rr_AnnualReturn2003

6.37%

2004

rr_AnnualReturn2004

3.82%

2005

rr_AnnualReturn2005

1.79%

2006

rr_AnnualReturn2006

4.12%

2007

rr_AnnualReturn2007

6.87%

2008

rr_AnnualReturn2008

5.64%

2009

rr_AnnualReturn2009

12.54%

2010

rr_AnnualReturn2010

7.45%

2011

rr_AnnualReturn2011

6.50%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

7.11%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Sep. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

5.58%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Jun. 30, 2004

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(2.99%)

Janus Flexible Bond Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class A

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class A Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[2]

1 Year

rr_AverageAnnualReturnYear01

1.38%

5 Years

rr_AverageAnnualReturnYear05

6.68%

10 Years

rr_AverageAnnualReturnYear10

5.92%

Since Inception

rr_AverageAnnualReturnSinceInception

7.31%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 07, 1987

Janus Flexible Bond Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class C

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class C Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[3]

1 Year

rr_AverageAnnualReturnYear01

4.63%

5 Years

rr_AverageAnnualReturnYear05

6.98%

10 Years

rr_AverageAnnualReturnYear10

5.73%

Since Inception

rr_AverageAnnualReturnSinceInception

6.85%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 07, 1987

Janus Flexible Bond Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class S

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class S Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

6.24%

5 Years

rr_AverageAnnualReturnYear05

7.54%

10 Years

rr_AverageAnnualReturnYear10

6.24%

Since Inception

rr_AverageAnnualReturnSinceInception

7.38%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 07, 1987

Janus Flexible Bond Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

6.66%

5 Years

rr_AverageAnnualReturnYear05

7.77%

10 Years

rr_AverageAnnualReturnYear10

6.46%

Since Inception

rr_AverageAnnualReturnSinceInception

7.54%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 07, 1987

Janus Flexible Bond Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class N

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class N Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

6.50%

5 Years

rr_AverageAnnualReturnYear05

7.77%

10 Years

rr_AverageAnnualReturnYear10

6.46%

Since Inception

rr_AverageAnnualReturnSinceInception

7.54%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 07, 1987

Janus Flexible Bond Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class R

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class R Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

5.98%

5 Years

rr_AverageAnnualReturnYear05

7.27%

10 Years

rr_AverageAnnualReturnYear10

5.99%

Since Inception

rr_AverageAnnualReturnSinceInception

7.12%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 07, 1987

Janus Flexible Bond Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

6.50%

5 Years

rr_AverageAnnualReturnYear05

7.77%

10 Years

rr_AverageAnnualReturnYear10

6.46%

Since Inception

rr_AverageAnnualReturnSinceInception

7.54%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 07, 1987

Janus Flexible Bond Fund | Class A, C, S, I, N, R, T Shares | Return After Taxes on Distributions | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

4.88%

5 Years

rr_AverageAnnualReturnYear05

5.92%

10 Years

rr_AverageAnnualReturnYear10

4.67%

Since Inception

rr_AverageAnnualReturnSinceInception

4.92%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 07, 1987

Janus Flexible Bond Fund | Class A, C, S, I, N, R, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

1 Year

rr_AverageAnnualReturnYear01

4.44%

5 Years

rr_AverageAnnualReturnYear05

5.61%

10 Years

rr_AverageAnnualReturnYear10

4.50%

Since Inception

rr_AverageAnnualReturnSinceInception

4.87%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 07, 1987

Janus Flexible Bond Fund | Class A, C, S, I, N, R, T Shares | Barclays U.S. Aggregate Bond Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Barclays U.S. Aggregate Bond Index

1 Year

rr_AverageAnnualReturnYear01

7.84%

5 Years

rr_AverageAnnualReturnYear05

6.50%

10 Years

rr_AverageAnnualReturnYear10

5.78%

Since Inception

rr_AverageAnnualReturnSinceInception

7.34%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 07, 1987

[1] Other Expenses for Class N Shares are based on the estimated expenses that the Shares expect to incur during their initial fiscal period.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

INTECH Global Dividend Fund | Class A, C, S, I, T Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

INTECH Global Dividend Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

INTECH Global Dividend Fund seeks long-term growth of capital and income.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

SHAREHOLDER FEES
(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

November 1, 2013

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the period December 15, 2011 to June 30, 2012, the Fund’s portfolio turnover rate was 24% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

24.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 46 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers or recoupments (if applicable) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

If Shares are redeemed:

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

If Shares are not redeemed:

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund invests, under normal circumstances, at least 80% of its net assets in dividend-paying securities. The Fund invests primarily in common stocks from the universe of the Morgan Stanley Capital International (“MSCI”) World High Dividend Yield Index, utilizing INTECH’s mathematical investment process. The MSCI World High Dividend Yield Index is designed to reflect the performance of the high dividend yield securities contained within the broader MSCI World Index^sm. The Fund may also invest in foreign equity and debt securities.

The Fund pursues its investment objective by applying a mathematical investment process to construct an investment portfolio from the universe of common stocks within its named benchmark index. The goal of this process is to build a portfolio of stocks in a more efficient combination than the named benchmark index. The process seeks to capitalize on the natural volatility of the market by searching for stocks within the index that have high relative volatility (providing the potential for excess returns) but that essentially move in opposite directions or have low correlation to each other (providing the potential for lower relative risk). By constructing the portfolio in this manner and periodically rebalancing the portfolio to maintain potentially more efficient weightings, INTECH’s mathematical investment process seeks to create a portfolio that, over time, produces returns in excess of its named benchmark index with risks similar to that of the benchmark index. The rebalancing techniques used by INTECH may result in a higher portfolio turnover compared to a “buy and hold” fund strategy.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Foreign Exposure Risk. The Fund normally has significant exposure to foreign markets as a result of its investments in foreign securities, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio.

Dividend Risk. Companies that issue dividend-yielding securities are not required to continue to pay dividends on such securities. Therefore, there is the possibility that such companies could reduce or eliminate the payment of dividends in the future.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Investment Process Risk. The proprietary mathematical investment process used by INTECH may not achieve the desired results. On an occasional basis, INTECH considers changes to its mathematical investment process. These changes may result in changes to the portfolio, might not provide the intended results, and may adversely impact the Fund’s performance.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

The biggest risk is that the Fund’s returns will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The Fund does not have a full calendar year of operations. Performance information for certain periods is included in the Fund’s first annual and/or semiannual report.

Performance One Year or Less [Text]

rr_PerformanceOneYearOrLess

The Fund does not have a full calendar year of operations.

INTECH Global Dividend Fund | Class A, C, S, I, T Shares | Class A

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class A

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class A

Management Fees

rr_ManagementFeesOverAssets

0.55%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

4.78%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

5.58%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

4.81%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.77%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleYear01

1,099

3 Years

rr_ExpenseExampleYear03

2,139

5 Years

rr_ExpenseExampleYear05

3,167

10 Years

rr_ExpenseExampleYear10

5,684

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

1,099

3 Years

rr_ExpenseExampleNoRedemptionYear03

2,139

5 Years

rr_ExpenseExampleNoRedemptionYear05

3,167

10 Years

rr_ExpenseExampleNoRedemptionYear10

5,684

INTECH Global Dividend Fund | Class A, C, S, I, T Shares | Class C

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class C

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

1.00%

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class C

Management Fees

rr_ManagementFeesOverAssets

0.55%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

4.78%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

6.33%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

4.81%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.52%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleYear01

729

3 Years

rr_ExpenseExampleYear03

1,861

5 Years

rr_ExpenseExampleYear05

3,061

10 Years

rr_ExpenseExampleYear10

5,925

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

629

3 Years

rr_ExpenseExampleNoRedemptionYear03

1,861

5 Years

rr_ExpenseExampleNoRedemptionYear05

3,061

10 Years

rr_ExpenseExampleNoRedemptionYear10

5,925

INTECH Global Dividend Fund | Class A, C, S, I, T Shares | Class S

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class S

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class S

Management Fees

rr_ManagementFeesOverAssets

0.55%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

5.04%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

5.84%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

4.82%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.02%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleYear01

582

3 Years

rr_ExpenseExampleYear03

1,730

5 Years

rr_ExpenseExampleYear05

2,859

10 Years

rr_ExpenseExampleYear10

5,600

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

582

3 Years

rr_ExpenseExampleNoRedemptionYear03

1,730

5 Years

rr_ExpenseExampleNoRedemptionYear05

2,859

10 Years

rr_ExpenseExampleNoRedemptionYear10

5,600

INTECH Global Dividend Fund | Class A, C, S, I, T Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class I

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class I

Management Fees

rr_ManagementFeesOverAssets

0.55%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

4.52%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

5.07%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

4.55%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.52%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleYear01

507

3 Years

rr_ExpenseExampleYear03

1,519

5 Years

rr_ExpenseExampleYear05

2,531

10 Years

rr_ExpenseExampleYear10

5,052

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

507

3 Years

rr_ExpenseExampleNoRedemptionYear03

1,519

5 Years

rr_ExpenseExampleNoRedemptionYear05

2,531

10 Years

rr_ExpenseExampleNoRedemptionYear10

5,052

INTECH Global Dividend Fund | Class A, C, S, I, T Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class T

Management Fees

rr_ManagementFeesOverAssets

0.55%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

4.98%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

5.53%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

4.76%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.77%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleYear01

552

3 Years

rr_ExpenseExampleYear03

1,646

5 Years

rr_ExpenseExampleYear05

2,729

10 Years

rr_ExpenseExampleYear10

5,386

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

552

3 Years

rr_ExpenseExampleNoRedemptionYear03

1,646

5 Years

rr_ExpenseExampleNoRedemptionYear05

2,729

10 Years

rr_ExpenseExampleNoRedemptionYear10

5,386

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, and Class S Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 0.50% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees. For a period of three years subsequent to the Fund's commencement of operations (December 15, 2011), Janus Capital may recover from the Fund fees and expenses previously waived or reimbursed, which could then be considered a deferral, if the Fund's expense ratio, including recovered expenses, falls below the expense limit.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Perkins Large Cap Value Fund | Class A, C, S, I, N, T Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Perkins Large Cap Value Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Perkins Large Cap Value Fund seeks capital appreciation.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

SHAREHOLDER FEES
(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 52% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

52.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 60 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

If Shares are redeemed:

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

If Shares are not redeemed:

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund pursues its investment objective by investing primarily in common stocks selected for their capital appreciation potential. The Fund primarily invests in the common stocks of large-sized companies whose stock prices the portfolio managers believe to be undervalued. The Fund invests, under normal circumstances, at least 80% of its net assets in equity securities of companies having, at the time of purchase, market capitalizations equal to or greater than the median market capitalization of companies included in the Russell 1000^® Value Index. The market capitalizations within the index will vary, but as of June 30, 2012, they ranged from approximately $1.3 billion to $400.1 billion, and the median market capitalization was $4.7 billion. The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets. The Fund may invest, under normal circumstances, up to 20% of its net assets in securities of companies having market capitalizations outside of the aforementioned market capitalization ranges. In addition, when the portfolio managers believe that market conditions are unfavorable for investing, or when they are otherwise unable to locate attractive investment opportunities, the Fund may invest up to 20% of its net assets in exchange-traded funds (“ETFs”), including commodity-related ETFs, cash or similar investments.

The Fund focuses on companies that have fallen out of favor with the market or that appear to be temporarily misunderstood by the investment community. The Fund’s portfolio managers generally look for companies with:

•   strong balance sheets and solid recurring free cash flows
•   attractive relative and absolute valuation ratios or that have underperformed recently
•   favorable reward to risk characteristics

The Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices, as substitutes for securities in which the Fund invests. The Fund may invest in derivative instruments (by taking long and/or short positions) for different purposes, including hedging (to offset risks associated with an investment, currency exposure, or market conditions) and to earn income and enhance returns. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s portfolio managers. When the Fund’s investments in cash or similar investments increase due to a lack of favorable investment opportunities or other extraordinary factors, the Fund may not participate in market advances or declines to the same extent that it would if the Fund had been fully invested.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio.

Exchange-Traded Funds Risk. The Fund may invest in ETFs which are typically open-end investment companies that are traded on a national securities exchange. ETFs typically incur fees, such as investment advisory fees and other operating expenses that are separate from those of the Fund, which will be indirectly paid by the Fund. As a result, the cost of investing in the Fund may be higher than the cost of investing directly in ETFs and may be higher than other mutual funds that invest directly in stocks and bonds. Further, the price movement of an ETF may fluctuate against the underlying securities or commodities it tracks and may result in a loss. Because the value of ETF shares depends on the demand in the market, the Fund may not be able to purchase or sell an ETF at the most optimal time, which could adversely affect the Fund’s performance.

The ETFs in which the Fund invests are subject to specific risks, depending on the investment strategy of the ETF. In turn, the Fund will be subject to substantially the same risks as those associated with direct exposure to the securities or commodities held by the ETF. Because the Fund may invest in a broad range of ETFs, such risks may include, but are not limited to, leverage risk, foreign exposure risk, and commodities risk.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

The biggest risk is that the Fund’s returns will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class I Shares, Class A Shares, Class C Shares, and Class S Shares of the Fund commenced operations on July 6, 2009, after the reorganization of each corresponding class of shares of Janus Adviser Perkins Large Cap Value Fund (“JAD predecessor fund”) into each respective share class of the Fund. Class T Shares of the Fund commenced operations on July 6, 2009. Class N Shares of the Fund commenced operations on May 31, 2012.

• The performance shown for Class I Shares, Class A Shares, Class C Shares, and Class S Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund’s Class I Shares, Class A Shares, Class C Shares, and Class S Shares prior to the reorganization, calculated using the fees and expenses of each respective share class of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class N Shares reflects the performance of the Fund’s Class I Shares from July 6, 2009 to December 31, 2011, calculated using the fees and expenses of Class I Shares, net of any applicable fee and expense limitations or waivers. The performance shown for Class N Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund’s Class I Shares prior to the reorganization, calculated using the fees and expenses of Class I Shares of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class T Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund’s Class I Shares prior to the reorganization, calculated using the fees and expenses of Class T Shares, without the effect of any fee and expense limitations or waivers.

If Class T Shares of the Fund had been available during periods prior to July 6, 2009, or Class N Shares of the Fund had been available during periods prior to December 31, 2011, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class I Shares, Class A Shares, Class C Shares, Class S Shares, Class N Shares, and Class T Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-877-335-2687

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/advisor/mutual-funds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class I Shares (calendar year-end)

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Second Quarter 2009 15.40%     Worst Quarter:  Third Quarter 2011  -14.75%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 13.59%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

After-tax returns are calculated using distributions for the Fund’s Class I Shares for periods following July 6, 2009; and for the JAD predecessor fund’s Class I Shares for periods prior to July 6, 2009. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Perkins Large Cap Value Fund | Class A, C, S, I, N, T Shares | Class A

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class A

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class A

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.62%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.26%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.13%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleYear01

684

3 Years

rr_ExpenseExampleYear03

913

5 Years

rr_ExpenseExampleYear05

1,161

10 Years

rr_ExpenseExampleYear10

1,871

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

684

3 Years

rr_ExpenseExampleNoRedemptionYear03

913

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,161

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,871

Perkins Large Cap Value Fund | Class A, C, S, I, N, T Shares | Class C

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class C

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

1.00%

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class C

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.62%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

0.30%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.92%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleYear01

295

3 Years

rr_ExpenseExampleYear03

603

5 Years

rr_ExpenseExampleYear05

1,037

10 Years

rr_ExpenseExampleYear10

2,243

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

195

3 Years

rr_ExpenseExampleNoRedemptionYear03

603

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,037

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,243

Perkins Large Cap Value Fund | Class A, C, S, I, N, T Shares | Class S

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class S

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class S

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.62%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.38%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.25%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleYear01

127

3 Years

rr_ExpenseExampleYear03

397

5 Years

rr_ExpenseExampleYear05

686

10 Years

rr_ExpenseExampleYear10

1,511

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

127

3 Years

rr_ExpenseExampleNoRedemptionYear03

397

5 Years

rr_ExpenseExampleNoRedemptionYear05

686

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,511

Perkins Large Cap Value Fund | Class A, C, S, I, N, T Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class I

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class I

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.62%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.15%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.77%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleYear01

79

3 Years

rr_ExpenseExampleYear03

246

5 Years

rr_ExpenseExampleYear05

428

10 Years

rr_ExpenseExampleYear10

954

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

79

3 Years

rr_ExpenseExampleNoRedemptionYear03

246

5 Years

rr_ExpenseExampleNoRedemptionYear05

428

10 Years

rr_ExpenseExampleNoRedemptionYear10

954

2009

rr_AnnualReturn2009

25.15%

2010

rr_AnnualReturn2010

12.19%

2011

rr_AnnualReturn2011

(0.20%)

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

13.59%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

15.40%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(14.75%)

Perkins Large Cap Value Fund | Class A, C, S, I, N, T Shares | Class N

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class N

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class N

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.62%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.14%

^[1]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.76%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class N Shares

1 Year

rr_ExpenseExampleYear01

78

3 Years

rr_ExpenseExampleYear03

243

5 Years

rr_ExpenseExampleYear05

422

10 Years

rr_ExpenseExampleYear10

942

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class N Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

78

3 Years

rr_ExpenseExampleNoRedemptionYear03

243

5 Years

rr_ExpenseExampleNoRedemptionYear05

422

10 Years

rr_ExpenseExampleNoRedemptionYear10

942

Perkins Large Cap Value Fund | Class A, C, S, I, N, T Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class T

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.62%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.38%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.00%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleYear01

102

3 Years

rr_ExpenseExampleYear03

318

5 Years

rr_ExpenseExampleYear05

552

10 Years

rr_ExpenseExampleYear10

1,225

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

102

3 Years

rr_ExpenseExampleNoRedemptionYear03

318

5 Years

rr_ExpenseExampleNoRedemptionYear05

552

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,225

Perkins Large Cap Value Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class A

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class A Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[2]

1 Year

rr_AverageAnnualReturnYear01

(6.25%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

9.40%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class C

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class C Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[3]

1 Year

rr_AverageAnnualReturnYear01

(2.20%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

10.74%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class S

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class S Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(0.72%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

11.36%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(0.20%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

11.90%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class N

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class N Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(0.20%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

11.90%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(0.41%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

11.49%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class A, C, S, I, N, T Shares | Return After Taxes on Distributions | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

(1.48%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

11.09%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class A, C, S, I, N, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[4]

1 Year

rr_AverageAnnualReturnYear01

0.81%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

10.04%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class A, C, S, I, N, T Shares | Russell 1000 Value Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Russell 1000^® Value Index

1 Year

rr_AverageAnnualReturnYear01

0.39%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

11.55%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

[1] Other Expenses for Class N Shares are based on the estimated expenses that the Shares expect to incur during their initial fiscal period.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

[4] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Janus Government Money Market Fund | Class D Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Janus Government Money Market Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVES

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Janus Government Money Market Fund seeks capital preservation and liquidity

Objective, Secondary [Text Block]

rr_ObjectiveSecondaryTextBlock

with current income as a secondary objective.

Expense [Heading]

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FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

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This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Expense Example [Heading]

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EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund pursues its investment objectives by investing exclusively in obligations issued and/or guaranteed as to principal and interest by the United States Government or by its agencies and instrumentalities, and repurchase agreements secured by such obligations. Although U.S. Government agencies and instrumentalities may be chartered or sponsored by Acts of Congress, their securities are not issued by, and may not be guaranteed by (i.e., backed by the full faith and credit of), the United States Treasury. Some government agency and instrumentality securities not backed by the full faith and credit of the United States are supported by the issuer’s ability to borrow from the U.S. Treasury, some are supported only by the credit of the issuer, and some are supported by the United States in some other way. For securities not backed by the full faith and credit of the U.S. Treasury, the Fund must look principally to the agency or instrumentality issuing or guaranteeing the securities for repayment and may not be able to assert a claim against the United States if the agency or instrumentality does not meet its commitment. The Fund’s investments in securities issued by U.S. Government agencies and instrumentalities may be significant.

The Fund will:

• invest in high quality, short-term money market instruments that present minimal credit risks, as determined by Janus Capital

• invest only in U.S. dollar-denominated instruments that have a remaining maturity of 397 days or less (as calculated pursuant to Rule 2a-7 under the Investment Company Act of 1940, as amended)

• maintain a dollar-weighted average portfolio maturity of 60 days or less and maintain a dollar-weighted average portfolio life (portfolio maturity measured without reference to any maturity shortening provisions of adjustable rate securities by reference to their interest rate reset dates) of 120 days or less

Risk [Heading]

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PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

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Market Risk. The Fund’s yield will vary as the short-term securities in its portfolio mature and the proceeds are reinvested in securities with different interest rates. For capital preservation and liquidity, the Fund may have a greater concentration in short-term securities including, but not limited to, investing up to all of its assets in overnight securities, which may result in a reduction of the Fund’s yield. Over time, the real value of the Fund’s yield may be eroded by inflation. Although the Fund invests only in high-quality, short-term money market instruments, there is a risk that the value of the securities it holds will fall as a result of changes in interest rates, an issuer’s actual or perceived creditworthiness, or an issuer’s ability to meet its obligations. The credit quality of the Fund’s holdings can change rapidly in certain market environments and any downgrade or default of a portfolio security could cause the Fund’s share price or yield to fall.

Collateral Risk. With respect to collateral received in repurchase transactions or other investments, the Fund may have significant exposure to government agencies not secured by the full faith and credit of the United States. Such exposure, depending on market conditions, could have a negative impact on the Fund, including minimizing the value of any collateral.

Money Market Risk. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund.

Risk Money Market Fund [Text]

rr_RiskMoneyMarketFund

Money Market Risk. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares, the predecessor share class. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses in effect during the periods shown, net of any applicable fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table shows how the Fund’s returns over different periods average out. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-800-525-3713

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/allfunds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class D Shares (calendar year-end)

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Fourth Quarter 2006  1.21%          Worst Quarter:  Third Quarter 2011  0.00%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 0.00%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Money Market Seven Day Yield, Caption [Text]

rr_MoneyMarketSevenDayYieldCaption

The 7-day yield on December 31, 2011 was 0.00% for Janus Government Money Market Fund.

Money Market Seven Day Yield

rr_MoneyMarketSevenDayYield

0.00%

Janus Government Money Market Fund | Class D Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class D

Management Fees

rr_ManagementFeesOverAssets

0.20%

Other Expenses

rr_OtherExpensesOverAssets

0.49%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.69%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class D Shares

1 Year

rr_ExpenseExampleYear01

70

3 Years

rr_ExpenseExampleYear03

221

5 Years

rr_ExpenseExampleYear05

384

10 Years

rr_ExpenseExampleYear10

859

2002

rr_AnnualReturn2002

1.33%

2003

rr_AnnualReturn2003

0.65%

2004

rr_AnnualReturn2004

0.85%

2005

rr_AnnualReturn2005

2.70%

2006

rr_AnnualReturn2006

4.52%

2007

rr_AnnualReturn2007

4.66%

2008

rr_AnnualReturn2008

1.83%

2009

rr_AnnualReturn2009

0.01%

2010

rr_AnnualReturn2010

0.02%

2011

rr_AnnualReturn2011

0.00%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

0.00%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Dec. 31, 2006

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

1.21%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

0.00%

Janus Government Money Market Fund | Class D Shares | Return Before Taxes | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

none

5 Years

rr_AverageAnnualReturnYear05

1.29%

10 Years

rr_AverageAnnualReturnYear10

1.64%

Since Inception

rr_AverageAnnualReturnSinceInception

2.99%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 14, 1995

XML

Janus High-Yield Fund | Class A, C, S, I, N, R, T Shares

Fund summary

Janus High-Yield Fund

INVESTMENT OBJECTIVES

Janus High-Yield Fund seeks to obtain high current income.

Capital appreciation is a secondary investment objective when consistent with its primary investment objective.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 51 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.

SHAREHOLDER FEES
(fees paid directly from your investment)

Shareholder Fees Janus High-Yield Fund Class A, C, S, I, N, R, T Shares	Class A	Class C	Class S	Class I	Class N	Class R	Class T
Shareholder Fees Column [Text]	Class A	Class C	Class S	Class I	Class N	Class R	Class T
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	4.75%	none	none	none	none	none	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	none	1.00%	none	none	none	none	none

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Janus High-Yield Fund Class A, C, S, I, N, R, T Shares	Class A	Class C	Class S	Class I	Class N		Class R	Class T
Operating Expenses Column [Text]	Class A	Class C	Class S	Class I	Class N		Class R	Class T
Management Fees	0.57%	0.57%	0.57%	0.57%	0.57%		0.57%	0.57%
Distribution/Service (12b-1) Fees	0.25%	1.00%	0.25%	none	none		0.50%	none
Other Expenses	0.17%	0.15%	0.29%	0.11%	0.04%	[1]	0.29%	0.29%
Total Annual Fund Operating Expenses	0.99%	1.72%	1.11%	0.68%	0.61%		1.36%	0.86%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

If Shares are redeemed:

Expense Example Janus High-Yield Fund Class A, C, S, I, N, R, T Shares (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	571	775	996	1,630
Class C	Class C Shares	275	542	933	2,030
Class S	Class S Shares	113	353	612	1,352
Class I	Class I Shares	69	218	379	847
Class N	Class N Shares	62	195	340	762
Class R	Class R Shares	138	431	745	1,635
Class T	Class T Shares	88	274	477	1,061

If Shares are not redeemed:

Expense Example, No Redemption Janus High-Yield Fund Class A, C, S, I, N, R, T Shares (USD $)	Expense Example, No Redemption, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	571	775	996	1,630
Class C	Class C Shares	175	542	933	2,030
Class S	Class S Shares	113	353	612	1,352
Class I	Class I Shares	69	218	379	847
Class N	Class N Shares	62	195	340	762
Class R	Class R Shares	138	431	745	1,635
Class T	Class T Shares	88	274	477	1,061

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 61% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objectives by investing, under normal circumstances, at least 80% of its net assets in high-yield/high-risk securities rated below investment grade. Securities rated below investment grade may include their unrated equivalents or other high-yielding securities the portfolio managers believe offer attractive risk/return characteristics. The Fund may at times invest all of its assets in such securities. The Fund may also invest in bank loans, money market instruments, and foreign debt securities (which may include investments in emerging markets). Due to the nature of securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

In addition, the Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. In particular, the Fund may use interest rate futures to manage portfolio risk. The Fund’s exposure to derivatives will vary. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

In addition to considering economic factors such as the effect of interest rates on the Fund’s investments, the portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income‒producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

PRINCIPAL INVESTMENT RISKS

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

High-Yield/High-Risk Bond Risk. The Fund may invest without limit in higher-yielding/higher-risk bonds, also known as “junk” bonds. High-yield/high-risk bonds may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Bank Loan Risk. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. Participation interests and assignments involve credit, interest rate, and liquidity risk. In addition, the bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. To the extent the Fund invests in foreign debt securities, such investments are sensitive to changes in interest rates. Additionally, investments in securities of foreign governments involve the risk that a foreign government may not be willing or able to pay interest or repay principal when due. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares, the initial share class) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class R Shares of the Fund commenced operations on July 6, 2009. Class N Shares of the Fund commenced operations on May 31, 2012.

• The performance shown for Class T Shares is calculated using the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class A Shares, Class C Shares, Class S Shares, and Class R Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers.
• The performance shown for Class I Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class N Shares for periods prior to December 31, 2011, reflects the performance of the Fund’s Class T Shares, calculated using the fees and expenses of Class T Shares, net of any applicable fee and expense limitations or waivers.

If Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class R Shares of the Fund had been available during periods prior to July 6, 2009, or Class N Shares of the Fund had been available during periods prior to December 31, 2011, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, Class I Shares, Class N Shares, and Class R Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Annual Total Returns for Class T Shares (calendar year-end)

Best Quarter:  Second Quarter 2009  14.93%          Worst Quarter:  Fourth Quarter 2008   −12.96%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 10.73%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Janus High-Yield Fund Class A, C, S, I, N, R, T Shares	Column	Label		1 Year	5 Years	10 Years	Since Inception	Inception Date
Class T Shares Return Before Taxes	Class T Shares	Return Before Taxes		3.20%	6.58%	7.42%	7.83%	Dec. 29, 1995
Class T Shares Return After Taxes on Distributions	Class T Shares	Return After Taxes On Distributions		0.64%	3.38%	4.48%	4.55%	Dec. 29, 1995
Class T Shares Return After Taxes on Distributions and Sale of Fund Shares	Class T Shares	Return After Taxes On Distributions and Sale of Fund Shares	[1]	2.07%	3.65%	4.56%	4.65%	Dec. 29, 1995
Class A Shares Return Before Taxes	Class A Shares	Return Before Taxes	[2]	(1.71%)	5.45%	6.82%	7.46%	Dec. 29, 1995
Class C Shares Return Before Taxes	Class C Shares	Return Before Taxes	[3]	1.37%	5.74%	6.59%	7.02%	Dec. 29, 1995
Class S Shares Return Before Taxes	Class S Shares	Return Before Taxes		2.95%	6.30%	7.12%	7.56%	Dec. 29, 1995
Class I Shares Return Before Taxes	Class I Shares	Return Before Taxes		3.36%	6.58%	7.42%	7.83%	Dec. 29, 1995
Class N Shares Return Before Taxes	Class N Shares	Return Before Taxes		3.20%	6.58%	7.42%	7.83%	Dec. 29, 1995
Class R Shares Return Before Taxes	Class R Shares	Return Before Taxes		2.74%	6.01%	6.85%	7.29%	Dec. 29, 1995
Barclays U.S. Corporate High-Yield Bond Index (reflects no deduction for expenses, fees, or taxes)		Barclays U.S. Corporate High-Yield Bond Index		4.98%	7.54%	8.85%	7.18%	Dec. 29, 1995

After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares, the initial share class). After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

[1] Other Expenses for Class N Shares are based on the estimated expenses that the Shares expect to incur during their initial fiscal period.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

XML

Janus Real Return Fund | Class A, C, S, I, T Shares

Fund summary

Janus Real Return Fund
(formerly named Janus Real Return Allocation Fund)

INVESTMENT OBJECTIVE

Janus Real Return Fund seeks real return consistent with preservation of capital.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 31 of the Fund’s Prospectus and in the “Purchases” section on page 56 of the Fund’s Statement of Additional Information.

SHAREHOLDER FEES
(fees paid directly from your investment)

Shareholder Fees Janus Real Return Fund Class A, C, S, I, T Shares

Class A

Class C

Class S

Class I

Class T

Shareholder Fees Column [Text]

Class A

Class C

Class S

Class I

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

4.75%

none

none

none

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

none

1.00%

none

none

none

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Janus Real Return Fund Class A, C, S, I, T Shares

Class A

Class C

Class S

Class I

Class T

Operating Expenses Column [Text]

Class A

Class C

Class S

Class I

Class T

Management Fees

0.55%

0.55%

0.55%

0.55%

0.55%

Distribution/Service (12b-1) Fees

0.25%

1.00%

0.25%

none

none

Other Expenses

^[1]

0.70%

0.69%

0.94%

0.69%

0.94%

Total Annual Fund Operating Expenses

^[2]

1.50%

2.24%

1.74%

1.24%

1.49%

Fee Waiver

^[2]

0.49%

0.48%

0.48%

0.48%

0.48%

Total Annual Fund Operating Expenses After Fee Waiver

^[2]

1.01%

1.76%

1.26%

0.76%

1.01%

EXAMPLE:

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers or recoupments (if applicable) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

If Shares are redeemed:

Expense Example Janus Real Return Fund Class A, C, S, I, T Shares (USD $)

Expense Example, By Year, Column [Text]

1 Year

3 Years

5 Years

10 Years

Class A

Class A Shares

620

926

1,253

2,177

Class C

Class C Shares

327

700

1,199

2,573

Class S

Class S Shares

177

547

943

2,049

Class I

Class I Shares

126

393

680

1,498

Class T

Class T Shares

151

470

812

1,777

If Shares are not redeemed:

Expense Example, No Redemption Janus Real Return Fund Class A, C, S, I, T Shares (USD $)

Expense Example, No Redemption, By Year, Column [Text]

1 Year

3 Years

5 Years

10 Years

Class A

Class A Shares

620

926

1,253

2,177

Class C

Class C Shares

227

700

1,199

2,573

Class S

Class S Shares

177

547

943

2,049

Class I

Class I Shares

126

393

680

1,498

Class T

Class T Shares

151

470

812

1,777

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 45% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objective by primarily investing in U.S. Treasury securities, short-duration high-yield/high-risk debt, commodity-linked investments, and equity securities. The Fund’s investments in U.S. Treasury securities may also include Treasury Inflation Protected Securities, also known as TIPS. As utilized by the Fund, each of these types of investments may be considered an “inflation-related investment,” which are those that may provide what is known as “real return,” or a rate of return above the rate of inflation over a full market cycle. Due to the nature of securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

The Fund may invest up to 90% of its net assets in short-duration high-yield/high-risk debt securities. The Fund’s investments in short-duration high-yield/high-risk securities include debt rated below investment grade, also known as “junk bonds.” Securities rated below investment grade may include their unrated equivalents or other high-yielding securities the portfolio managers believe offer attractive risk/return characteristics. The Fund may also invest in certain investment grade debt instruments, including corporate bonds, government bonds, municipal bonds, mortgage-backed securities, zero-coupon bonds, and agency securities. The Fund may invest in foreign debt securities.

To seek exposure to the commodities markets, the Fund may invest in commodity-linked investments such as commodity-related exchange-traded funds (“ETFs”), commodity index-linked swap agreements, commodity options and futures, and options on futures that provide exposure to the investment returns of the commodities markets. The Fund may also invest in other commodity-linked derivative instruments, such as commodity-linked notes (“structured notes”).

The Fund’s investments in equity securities may include common stock, preferred stock, and convertible securities, all of which may include exposure to foreign markets. The Fund may invest in companies of any market capitalization. The Fund’s equity investments may also include securities of real estate-related companies, including, but not limited to, real estate investment trusts (“REITs”) and similar REIT-like entities, such as foreign entities that have REIT characteristics.

The Fund may also invest in derivative instruments (by taking long and/or short positions) for various purposes, including hedging by shorting interest rate futures against long positions in TIPS, using inflation index swaps to hedge against unexpected changes in the rate of inflation, using interest rate swaps to hedge against changes in interest rates, to increase or decrease the Fund’s exposure to a particular market, to manage or adjust the risk profile of the Fund related to an investment, and to earn income and enhance returns. The Fund’s exposure to derivatives will vary, is not limited to those derivatives listed, and could be significant at times. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

The Fund may also use reverse repurchase agreements to generate income as part of its inflation-related strategies. Proceeds from reverse repurchase agreement transactions may be invested in other securities or instruments to attempt to increase the Fund’s investment return. The Fund may also invest in money market instruments, buy backs or dollar rolls, other securitized debt products, bank loans, various when-issued securities, exchange-traded notes, and other investment companies.

In addition to considering economic factors such as the rate of inflation and the effect of interest rates on the Fund’s investments, the portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

PRINCIPAL INVESTMENT RISKS

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Inflation-Related Investment Risk. Inflation index swaps and other inflation-linked securities are subject to inflation risk. A swap held long by the Fund can potentially lose value if the rate of inflation over the life of the swap is less than the fixed rate that the Fund agrees to pay at the initiation of the swap. Except for the Fund’s investments in U.S. Treasury securities, which are guaranteed as to principal by the U.S. Treasury, the inflation-adjusted principal value of inflation-linked securities repaid at maturity may be less than the original principal. Because of the inflation-linked adjustment feature, inflation-linked securities typically have lower yields than conventional fixed-rate securities. In the event of deflation, where prices decline over time, the principal and income of inflation-linked securities will likely decline, resulting in losses to the Fund.

High-Yield/High-Risk Bond Risk. The Fund may invest up to 90% of its net assets in higher-yielding/higher-risk bonds, also known as “junk” bonds. High-yield/high-risk bonds may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Commodity-Linked Investments Risk. The Fund may invest in various commodity-linked investments that provide exposure to the commodities markets. Such exposure may subject the Fund to greater volatility than investments in traditional securities. The value of a given commodity-linked derivative investment typically is based upon the price movements of a physical commodity (such as heating oil, livestock, or agricultural products), a commodity futures contract or commodity index, or some other readily measurable economic variable. The value of commodity-linked derivative instruments may therefore be affected by changes in overall market movements, volatility of the underlying benchmark, changes in interest rates, or other factors affecting a particular industry or commodity such as drought, floods, weather, livestock disease, embargoes, tariffs, and international economic, political, and regulatory developments.

Exchange-Traded Funds Risk. The Fund may invest in ETFs which are typically open-end investment companies that are traded on a national securities exchange. ETFs typically incur fees, such as investment advisory fees and other operating expenses that are separate from those of the Fund, which will be indirectly paid by the Fund. As a result, the cost of investing in the Fund may be higher than the cost of investing directly in ETFs and may be higher than other mutual funds that invest directly in stocks and bonds. Further, the price movement of an ETF may fluctuate against the underlying securities or commodities it tracks and may result in a loss. Because the value of ETF shares depends on the demand in the market, the Fund may not be able to purchase or sell an ETF at the most optimal time, which could adversely affect the Fund’s performance.

The ETFs in which the Fund invests are subject to specific risks, depending on the investment strategy of the ETF. In turn, the Fund will be subject to substantially the same risks as those associated with direct exposure to the securities or commodities held by the ETF. Because the Fund may invest in a broad range of ETFs, such risks may include, but are not limited to, leverage risk, foreign exposure risk, and commodities risk.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Sovereign Debt Risk. The Fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However, investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited.

Counterparty Risk. Certain derivative and “over-the-counter” instruments, such as swaps and forwards, are subject to the risk that the other party to a contract will not fulfill its contractual obligations.

Leverage Risk. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. In particular, certain commodity-linked investments may subject the Fund to leveraged market exposure to commodities. Leverage also occurs when the Fund increases its assets available for investment through borrowings, reverse repurchase agreements, or similar transactions. The Fund’s use of leverage can magnify the effect of any gains or losses, causing the Fund to be more volatile than if it had not been leveraged. There is no assurance that any leveraging strategy will be successful.

Reverse Repurchase Agreement Risk. Reverse repurchase agreements involve leverage risk, counterparty risk, and the risk that the value of securities that the Fund is obligated to repurchase under the agreement may decline below the repurchase price. When the Fund invests reverse repurchase transaction proceeds, the Fund is at risk for any fluctuations in the value of securities in which the proceeds are invested. To the extent the Fund uses reverse repurchase agreements, the value of an investment in the Fund may be more volatile, and such transactions may increase the Fund’s overall investment exposure. Additionally, interest expenses related to reverse repurchase transactions could exceed the rate of return on debt obligations and other investments held by the Fund, thereby reducing returns to shareholders.

Foreign Exposure Risk. The Fund normally has significant exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Growth Securities Risk. The Fund invests in companies after assessing their growth potential. Securities of companies perceived to be “growth” companies may be more volatile than other stocks and may involve special risks. If the portfolio managers’ perception of a company’s growth potential is not realized, the securities purchased may not perform as expected, reducing the Fund’s returns. In addition, because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “growth” stocks may perform differently from the market as a whole and other types of securities.

Real Estate Risk. An investment in the Fund may be subject to many of the same risks as a direct investment in real estate. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

Nondiversification Risk. The Fund is classified as nondiversified under the Investment Company Act of 1940, as amended. This gives the Fund’s portfolio managers more flexibility to hold larger positions in a smaller number of securities. As a result, an increase or decrease in the value of a single security held by the Fund may have a greater impact on the Fund’s net asset value and total return.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The Fund does not have a full calendar year of operations. Performance information for certain periods is included in the Fund’s first annual and/or semiannual report.

[1] Other Expenses are based on the estimated expenses that the Fund expects to incur.

[2] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, and Class S Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 0.76% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees. For a period of three years subsequent to the Fund's commencement of operations (May 13, 2011) or until the Fund's assets exceed the first breakpoint in the investment advisory fee schedule, whichever occurs first, Janus Capital may recover from the Fund fees and expenses previously waived or reimbursed, which could then be considered a deferral, if the Fund's expense ratio, including recovered expenses, falls below the expense limit.

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Perkins Value Plus Income Fund | Class A, C, S, I, N, T Shares

Fund summary

Perkins Value Plus Income Fund

INVESTMENT OBJECTIVE

Perkins Value Plus Income Fund seeks capital appreciation and current income.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 60 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.

SHAREHOLDER FEES
(fees paid directly from your investment)

Shareholder Fees Perkins Value Plus Income Fund Class A, C, S, I, N, T Shares	Class A	Class C	Class S	Class I	Class N	Class T
Shareholder Fees Column [Text]	Class A	Class C	Class S	Class I	Class N	Class T
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	5.75%	none	none	none	none	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	none	1.00%	none	none	none	none

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Perkins Value Plus Income Fund Class A, C, S, I, N, T Shares		Class A	Class C	Class S	Class I	Class N		Class T
Operating Expenses Column [Text]		Class A	Class C	Class S	Class I	Class N		Class T
Management Fees		0.60%	0.60%	0.60%	0.60%	0.60%		0.60%
Distribution/Service (12b-1) Fees		0.25%	1.00%	0.25%	none	none		none
Other Expenses		0.65%	0.66%	0.88%	0.65%	0.63%	[1]	0.88%
Total Annual Fund Operating Expenses	[2]	1.50%	2.26%	1.73%	1.25%	1.23%		1.48%
Fee Waiver	[2]	0.48%	0.49%	0.46%	0.48%	0.46%		0.46%
Total Annual Fund Operating Expenses After Fee Waiver	[2]	1.02%	1.77%	1.27%	0.77%	0.77%		1.02%

EXAMPLE:

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers or recoupments (if applicable) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

If Shares are redeemed:

Expense Example Perkins Value Plus Income Fund Class A, C, S, I, N, T Shares (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	719	1,022	1,346	2,263
Class C	Class C Shares	329	706	1,210	2,595
Class S	Class S Shares	176	545	939	2,041
Class I	Class I Shares	127	397	686	1,511
Class N	Class N Shares	125	390	676	1,489
Class T	Class T Shares	151	468	808	1,768

If Shares are not redeemed:

Expense Example, No Redemption Perkins Value Plus Income Fund Class A, C, S, I, N, T Shares (USD $)	Expense Example, No Redemption, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	719	1,022	1,346	2,263
Class C	Class C Shares	229	706	1,210	2,595
Class S	Class S Shares	176	545	939	2,041
Class I	Class I Shares	127	397	686	1,511
Class N	Class N Shares	125	390	676	1,489
Class T	Class T Shares	151	468	808	1,768

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 100% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objective by normally investing 40-60% of its assets in equity securities selected primarily for capital appreciation and investing the remainder in fixed-income securities and cash equivalents.

Equity Securities. The Fund’s equity investments generate total return from a combination of capital appreciation and, to a lesser degree, current income. Such equity investments may include companies of any size, but the Fund will invest primarily in large- and mid-sized companies whose stock prices the portfolio managers believe to be undervalued or have the potential for high relative dividend yields, or both. The Fund’s equity portfolio managers invest in companies which have fallen out of favor with the market or that appear to be temporarily misunderstood by the investment community. The Fund’s equity portfolio managers generally look for companies with:

• strong balance sheets and solid recurring free cash flows
• attractive relative and absolute valuation ratios or that have underperformed recently
• favorable reward to risk characteristics

Fixed-Income Securities. The Fund’s fixed-income investments generate total return from a combination of current income and capital appreciation, but income is usually the dominant portion. The Fund normally invests the portion of its assets allocated to fixed-income investments in debt securities (including, but not limited to, government bonds, corporate bonds, mortgage-backed securities, asset-backed securities, zero-coupon bonds, and bank loans), convertible securities, and short-term securities. The Fund invests at least 50% of the fixed-income portion of its assets in investment grade debt securities. The Fund will limit its investment in high-yield/high-risk bonds, also known as “junk” bonds, to 50% or less of the fixed-income portion of its net assets.

In addition to considering economic factors such as the effect of interest rates on the Fund’s fixed-income investments, the Fund’s fixed-income portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income-producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets.

The Fund may also invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. The Fund has and is expected to continue to buy and sell put and call options to enhance returns. The Fund’s exposure to derivatives will vary, is not limited to those derivatives listed, and could be significant at times. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

Janus Capital is primarily responsible for the overall asset allocation of the Fund and manages the Fund’s fixed-income investments. Cash positions are considered a part of the Fund’s fixed-income allocation and will be managed by the Fund’s fixed-income portfolio managers. Perkins manages the Fund’s equity investments and assists the adviser in determining the Fund’s overall asset allocation. The Fund may periodically adjust its mix of equity and fixed-income investments in response to changing economic and market conditions, including outside the range of 40-60% of its assets in equity securities. Due to the nature of the fixed-income securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns and yields will vary, and you could lose money. The Fund is designed for long-term investors seeking a portfolio including common stocks and bonds selected for their potential to produce capital appreciation and current income. Common stocks tend to be more volatile than many other investment choices.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s equity portfolio managers.

Mid-Sized Companies Risk. The Fund’s investments in securities issued by mid-sized companies may involve greater risks than are customarily associated with larger, more established companies. Securities issued by mid-sized companies tend to be more volatile than securities issued by larger or more established companies and may underperform as compared to the securities of larger companies.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

High-Yield/High-Risk Bond Risk. High-yield/high-risk bonds may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Bank Loan Risk. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. Participation interests and assignments involve credit, interest rate, and liquidity risk. In addition, the bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

Foreign Exposure Risk. The Fund may have significant exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited.

Allocation Risk. The Fund’s ability to achieve its investment objective depends largely upon the allocation of assets among the equity and fixed asset categories. You could lose money on your investment in the Fund as a result of these allocations. Portfolio management may favor an asset category that underperforms relative to other asset categories. For example, the Fund may be overweighted in equity securities when the stock market is falling and the fixed-income market is rising. Additionally, periodic rebalancing of Fund assets among asset categories may result in increased transaction costs, which may have a negative effect on the Fund’s performance.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class T Shares of the Fund commenced operations with the Fund’s inception.

• The performance shown for Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class T Shares is calculated using the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class N Shares reflects the performance of the Fund’s Class I Shares, calculated using the fees and expenses of Class N Shares, without the effect of any fee and expense limitations or waivers. If Class N Shares of the Fund had been available during the periods shown, the performance may have been different.

The bar chart depicts the Fund’s performance during the period indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Annual Total Returns for Class I Shares (calendar year-end)

Best Quarter:  Fourth Quarter 2011  7.22%        Worst Quarter:  Third Quarter 2011 −7.73%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 10.53%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Perkins Value Plus Income Fund Class A, C, S, I, N, T Shares	Column	Label		1 Year	Since Inception	Inception Date
Class I Shares Return Before Taxes	Class I Shares	Return Before Taxes		3.74%	9.28%	Jul. 30, 2010
Class I Shares Return After Taxes on Distributions	Class I Shares	Return After Taxes on Distributions		1.66%	7.43%	Jul. 30, 2010
Class I Shares Return After Taxes on Distributions and Sale of Fund Shares	Class I Shares	Return After Taxes on Distributions and Sale of Fund Shares	[1]	2.73%	6.97%	Jul. 30, 2010
Class A Shares Return Before Taxes	Class A Shares	Return Before Taxes	[2]	(2.44%)	4.63%	Jul. 30, 2010
Class C Shares Return Before Taxes	Class C Shares	Return Before Taxes	[3]	1.79%	8.27%	Jul. 30, 2010
Class S Shares Return Before Taxes	Class S Shares	Return Before Taxes		3.27%	8.80%	Jul. 30, 2010
Class N Shares Return Before Taxes	Class N Shares	Return Before Taxes		3.29%	8.81%	Jul. 30, 2010
Class T Shares Return Before Taxes	Class T Shares	Return Before Taxes		3.54%	9.08%	Jul. 30, 2010
Russell 1000 Value Index (reflects no deduction for expenses, fees, or taxes)		Russell 1000® Value Index		0.39%	9.97%	Jul. 30, 2010
Barclays U.S. Aggregate Bond Index (reflects no deduction for expenses, fees, or taxes)		Barclays U.S. Aggregate Bond Index		7.84%	5.51%	Jul. 30, 2010
Value Income Index (reflects no deduction for expenses, fees, or taxes)		Value Income Index		4.44%	8.16%	Jul. 30, 2010

The Value Income Index is an internally-calculated, hypothetical combination of unmanaged indices that combines total returns from the Russell 1000^® Value Index (50%) and the Barclays U.S. Aggregate Bond Index (50%).

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

[1] Other Expenses for Class N Shares are based on the estimated expenses that the Shares expect to incur during their initial fiscal period.

[2] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, and Class S Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 0.76% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees. For a period of three years subsequent to the Fund's commencement of operations (July 30, 2010), Janus Capital may recover from the Fund fees and expenses previously waived or reimbursed, which could then be considered a deferral, if the Fund's expense ratio, including recovered expenses, falls below the expense limit.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Perkins Value Plus Income Fund | Class A, C, S, I, N, T Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Perkins Value Plus Income Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Perkins Value Plus Income Fund seeks capital appreciation and current income.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

SHAREHOLDER FEES
(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

November 1, 2013

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 100% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

100.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 60 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers or recoupments (if applicable) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

If Shares are redeemed:

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

If Shares are not redeemed:

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund pursues its investment objective by normally investing 40-60% of its assets in equity securities selected primarily for capital appreciation and investing the remainder in fixed-income securities and cash equivalents.

Equity Securities. The Fund’s equity investments generate total return from a combination of capital appreciation and, to a lesser degree, current income. Such equity investments may include companies of any size, but the Fund will invest primarily in large- and mid-sized companies whose stock prices the portfolio managers believe to be undervalued or have the potential for high relative dividend yields, or both. The Fund’s equity portfolio managers invest in companies which have fallen out of favor with the market or that appear to be temporarily misunderstood by the investment community. The Fund’s equity portfolio managers generally look for companies with:

• strong balance sheets and solid recurring free cash flows
• attractive relative and absolute valuation ratios or that have underperformed recently
• favorable reward to risk characteristics

Fixed-Income Securities. The Fund’s fixed-income investments generate total return from a combination of current income and capital appreciation, but income is usually the dominant portion. The Fund normally invests the portion of its assets allocated to fixed-income investments in debt securities (including, but not limited to, government bonds, corporate bonds, mortgage-backed securities, asset-backed securities, zero-coupon bonds, and bank loans), convertible securities, and short-term securities. The Fund invests at least 50% of the fixed-income portion of its assets in investment grade debt securities. The Fund will limit its investment in high-yield/high-risk bonds, also known as “junk” bonds, to 50% or less of the fixed-income portion of its net assets.

In addition to considering economic factors such as the effect of interest rates on the Fund’s fixed-income investments, the Fund’s fixed-income portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income-producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets.

The Fund may also invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. The Fund has and is expected to continue to buy and sell put and call options to enhance returns. The Fund’s exposure to derivatives will vary, is not limited to those derivatives listed, and could be significant at times. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

Janus Capital is primarily responsible for the overall asset allocation of the Fund and manages the Fund’s fixed-income investments. Cash positions are considered a part of the Fund’s fixed-income allocation and will be managed by the Fund’s fixed-income portfolio managers. Perkins manages the Fund’s equity investments and assists the adviser in determining the Fund’s overall asset allocation. The Fund may periodically adjust its mix of equity and fixed-income investments in response to changing economic and market conditions, including outside the range of 40-60% of its assets in equity securities. Due to the nature of the fixed-income securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The biggest risk is that the Fund’s returns and yields will vary, and you could lose money. The Fund is designed for long-term investors seeking a portfolio including common stocks and bonds selected for their potential to produce capital appreciation and current income. Common stocks tend to be more volatile than many other investment choices.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s equity portfolio managers.

Mid-Sized Companies Risk. The Fund’s investments in securities issued by mid-sized companies may involve greater risks than are customarily associated with larger, more established companies. Securities issued by mid-sized companies tend to be more volatile than securities issued by larger or more established companies and may underperform as compared to the securities of larger companies.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

High-Yield/High-Risk Bond Risk. High-yield/high-risk bonds may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Bank Loan Risk. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. Participation interests and assignments involve credit, interest rate, and liquidity risk. In addition, the bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

Foreign Exposure Risk. The Fund may have significant exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited.

Allocation Risk. The Fund’s ability to achieve its investment objective depends largely upon the allocation of assets among the equity and fixed asset categories. You could lose money on your investment in the Fund as a result of these allocations. Portfolio management may favor an asset category that underperforms relative to other asset categories. For example, the Fund may be overweighted in equity securities when the stock market is falling and the fixed-income market is rising. Additionally, periodic rebalancing of Fund assets among asset categories may result in increased transaction costs, which may have a negative effect on the Fund’s performance.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

The biggest risk is that the Fund’s returns and yields will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class T Shares of the Fund commenced operations with the Fund’s inception.

• The performance shown for Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class T Shares is calculated using the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class N Shares reflects the performance of the Fund’s Class I Shares, calculated using the fees and expenses of Class N Shares, without the effect of any fee and expense limitations or waivers. If Class N Shares of the Fund had been available during the periods shown, the performance may have been different.

The bar chart depicts the Fund’s performance during the period indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the Fund’s performance during the period indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-877-335-2687

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/advisor/mutual-funds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class I Shares (calendar year-end)

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Fourth Quarter 2011  7.22%        Worst Quarter:  Third Quarter 2011 −7.73%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 10.53%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The Value Income Index is an internally-calculated, hypothetical combination of unmanaged indices that combines total returns from the Russell 1000^® Value Index (50%) and the Barclays U.S. Aggregate Bond Index (50%).

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Perkins Value Plus Income Fund | Class A, C, S, I, N, T Shares | Class A

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class A

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class A

Management Fees

rr_ManagementFeesOverAssets

0.60%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.65%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.50%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.48%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.02%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleYear01

719

3 Years

rr_ExpenseExampleYear03

1,022

5 Years

rr_ExpenseExampleYear05

1,346

10 Years

rr_ExpenseExampleYear10

2,263

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

719

3 Years

rr_ExpenseExampleNoRedemptionYear03

1,022

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,346

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,263

Perkins Value Plus Income Fund | Class A, C, S, I, N, T Shares | Class C

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class C

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

1.00%

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class C

Management Fees

rr_ManagementFeesOverAssets

0.60%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

0.66%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

2.26%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.49%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.77%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleYear01

329

3 Years

rr_ExpenseExampleYear03

706

5 Years

rr_ExpenseExampleYear05

1,210

10 Years

rr_ExpenseExampleYear10

2,595

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

229

3 Years

rr_ExpenseExampleNoRedemptionYear03

706

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,210

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,595

Perkins Value Plus Income Fund | Class A, C, S, I, N, T Shares | Class S

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class S

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class S

Management Fees

rr_ManagementFeesOverAssets

0.60%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.88%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.73%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.46%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.27%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleYear01

176

3 Years

rr_ExpenseExampleYear03

545

5 Years

rr_ExpenseExampleYear05

939

10 Years

rr_ExpenseExampleYear10

2,041

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

176

3 Years

rr_ExpenseExampleNoRedemptionYear03

545

5 Years

rr_ExpenseExampleNoRedemptionYear05

939

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,041

Perkins Value Plus Income Fund | Class A, C, S, I, N, T Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class I

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class I

Management Fees

rr_ManagementFeesOverAssets

0.60%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.65%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.25%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.48%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.77%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleYear01

127

3 Years

rr_ExpenseExampleYear03

397

5 Years

rr_ExpenseExampleYear05

686

10 Years

rr_ExpenseExampleYear10

1,511

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

127

3 Years

rr_ExpenseExampleNoRedemptionYear03

397

5 Years

rr_ExpenseExampleNoRedemptionYear05

686

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,511

2011

rr_AnnualReturn2011

3.74%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

10.53%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Dec. 31, 2011

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

7.22%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(7.73%)

Perkins Value Plus Income Fund | Class A, C, S, I, N, T Shares | Class N

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class N

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class N

Management Fees

rr_ManagementFeesOverAssets

0.60%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.63%

^[2]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.23%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.46%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.77%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class N Shares

1 Year

rr_ExpenseExampleYear01

125

3 Years

rr_ExpenseExampleYear03

390

5 Years

rr_ExpenseExampleYear05

676

10 Years

rr_ExpenseExampleYear10

1,489

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class N Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

125

3 Years

rr_ExpenseExampleNoRedemptionYear03

390

5 Years

rr_ExpenseExampleNoRedemptionYear05

676

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,489

Perkins Value Plus Income Fund | Class A, C, S, I, N, T Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class T

Management Fees

rr_ManagementFeesOverAssets

0.60%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.88%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.48%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.46%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.02%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleYear01

151

3 Years

rr_ExpenseExampleYear03

468

5 Years

rr_ExpenseExampleYear05

808

10 Years

rr_ExpenseExampleYear10

1,768

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

151

3 Years

rr_ExpenseExampleNoRedemptionYear03

468

5 Years

rr_ExpenseExampleNoRedemptionYear05

808

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,768

Perkins Value Plus Income Fund | Class A, C, S, I, N, T Shares | Return After Taxes on Distributions | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

1.66%

Since Inception

rr_AverageAnnualReturnSinceInception

7.43%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 30, 2010

Perkins Value Plus Income Fund | Class A, C, S, I, N, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[3]

1 Year

rr_AverageAnnualReturnYear01

2.73%

Since Inception

rr_AverageAnnualReturnSinceInception

6.97%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 30, 2010

Perkins Value Plus Income Fund | Class A, C, S, I, N, T Shares | Russell 1000 Value Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Russell 1000^® Value Index

1 Year

rr_AverageAnnualReturnYear01

0.39%

Since Inception

rr_AverageAnnualReturnSinceInception

9.97%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 30, 2010

Perkins Value Plus Income Fund | Class A, C, S, I, N, T Shares | Barclays U.S. Aggregate Bond Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Barclays U.S. Aggregate Bond Index

1 Year

rr_AverageAnnualReturnYear01

7.84%

Since Inception

rr_AverageAnnualReturnSinceInception

5.51%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 30, 2010

Perkins Value Plus Income Fund | Class A, C, S, I, N, T Shares | Value Income Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Value Income Index

1 Year

rr_AverageAnnualReturnYear01

4.44%

Since Inception

rr_AverageAnnualReturnSinceInception

8.16%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 30, 2010

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, and Class S Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 0.76% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees. For a period of three years subsequent to the Fund's commencement of operations (July 30, 2010), Janus Capital may recover from the Fund fees and expenses previously waived or reimbursed, which could then be considered a deferral, if the Fund's expense ratio, including recovered expenses, falls below the expense limit.

[2] Other Expenses for Class N Shares are based on the estimated expenses that the Shares expect to incur during their initial fiscal period.

[3] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Janus Moderate Allocation Fund | Class A, C, S, I, T Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Janus Moderate Allocation Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Janus Moderate Allocation Fund seeks total return through growth of capital and income.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

SHAREHOLDER FEES
(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 18% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

18.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 45 of the Fund’s Prospectus and in the “Purchases” section on page 63 of the Fund’s Statement of Additional Information.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses (including the operating expenses of the underlying funds) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

If Shares are redeemed:

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

If Shares are not redeemed:

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund seeks to achieve its investment objective by investing in other Janus mutual funds (“underlying funds”) that represent a variety of asset classes and investment styles. The Fund pursues this objective by investing in a diversified portfolio of underlying funds resulting in an allocation of the Fund’s investments that normally provides exposure of approximately 60% to stocks and 40% to bonds and money market securities. The target allocation and the allocation of the Fund’s assets among underlying funds are based on quantitative and qualitative analysis. Because it invests in other funds, the Fund is considered a “fund of funds.”

The Fund’s asset allocation is intended to diversify investments among stocks, bonds, and cash equivalents. The portfolio manager regularly reviews the allocation of Fund assets in the underlying funds and may modify the underlying funds’ weightings or substitute other underlying funds to emphasize and mitigate risk exposures that may arise as a result of the implementation of the allocations. An independent asset allocation service provides evaluations of asset allocations that the portfolio manager may use in implementing the allocations among the underlying funds. The portfolio manager continually monitors asset class allocations and periodically rebalances the Fund’s investments in the underlying funds. The portfolio manager may change the Fund’s asset class allocations, the underlying funds, an underlying fund’s asset category, or weightings among asset classes or underlying funds without prior shareholder notice.

The Fund will normally allocate approximately 60% of its investments to underlying funds that provide varying exposure to common stocks of large U.S.-based companies, small- to mid-capitalization companies, and international companies (including those with exposure to emerging markets); and approximately 40% of its investments to underlying bond funds and money market instruments. Refer to Appendix A in this Prospectus for a brief description of the investment strategies of each of the currently available underlying funds.

When market conditions dictate a more defensive strategy, the Fund or an underlying fund may temporarily hold cash or invest its assets in temporary investments. In that case, the Fund may take positions that are inconsistent with its investment objective. As a result, the Fund may not achieve its investment objective.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking growth of capital and income. Investments in a portfolio with common stock exposure tend to be more volatile than many other investment choices.

Main Risks Associated with the Fund
Allocation Risk. The Fund’s ability to achieve its investment objective depends largely upon the portfolio manager’s allocation of assets among the underlying funds and other securities, using the optimization process (a process that utilizes quantitative analysis of a number of factors, such as historical risk, performance, fund classifications, and the relationship among underlying funds) and the judgment of the portfolio manager. You could lose money on your investment in the Fund as a result of these allocations. The Fund will typically invest in a number of different underlying funds; however, to the extent that the Fund invests a significant portion of its assets in a single underlying fund, it will be more sensitive to the risks associated with that fund and any investments in which that fund concentrates.

Affiliated Fund Risk. Janus Capital has the authority to select and substitute underlying affiliated mutual funds. The fees paid to Janus Capital by some Janus mutual funds are generally higher than the fees paid to Janus Capital by the Fund or by other funds and share classes available for investment by the Fund. These conditions may create a conflict of interest when selecting underlying affiliated mutual funds and share classes for investment. Janus Capital, however, is a fiduciary to the Fund and its shareholders and is legally obligated to act in their best interest when selecting underlying affiliated mutual funds.

Main Risks Associated with the Underlying Funds and Securities
The biggest risk is that the underlying funds’ returns will vary, and you could lose money.

Market Risk. Approximately 60% of the Fund’s assets are allocated to equity investments through investments in underlying funds. The value of an underlying fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if a portfolio manager’s belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of an underlying fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Fixed-Income Securities Risk. Approximately 40% of the Fund’s assets are allocated to fixed-income securities through investments in underlying funds. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause an underlying fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which an underlying fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that an underlying fund’s portfolio manager would like or at the price that the portfolio manager believes the security is currently worth.

Foreign Exposure Risk. Certain underlying funds may have significant exposure to foreign markets as a result of their investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, an underlying fund’s returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. A market swing in one or more countries or regions where an underlying fund has invested a significant amount of its assets may have a greater effect on an underlying fund’s performance than it would in a more geographically diversified portfolio. An underlying fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Emerging Markets Risk. The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities involve a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. In addition, an underlying fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of an underlying fund’s investments. To the extent that an underlying fund invests a significant portion of its assets in the securities of issuers in or companies of a single country or region, it is more likely to be impacted by events or conditions affecting that country or region, which could have a negative impact on the Fund’s performance. Some of the risks of investing directly in foreign and emerging market securities may be reduced when an underlying fund invests indirectly in foreign securities through various other investment vehicles including derivatives, which also involve other risks.

Sovereign Debt Risk. An underlying fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Exchange-Traded Funds Risk. Certain underlying funds may purchase shares of exchange-traded funds (“ETFs”) to gain exposure to a particular portion of the market. ETFs are pooled investment vehicles, which may be managed or unmanaged, that generally seek to track the performance of a specific index. ETFs are traded on an exchange at market prices that may vary from the net asset value of their underlying investments. When an underlying fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF’s expenses. ETFs have certain inherent risks generally associated with investments in a portfolio of securities in which the ETF is invested, including the risk that the general level of stock prices may decline, thereby adversely affecting the value of each unit of the ETF. ETFs also involve the risk that an active trading market for an ETF’s shares may not develop or be maintained.

Exchange-Traded Notes Risk. Certain underlying funds may invest in exchange-traded notes (“ETNs”), which are debt securities whose returns are linked to a particular index. ETNs are typically linked to the performance of a commodities index that reflects the potential return on unleveraged investments in futures contracts of physical commodities, plus a specified rate of interest that could be earned on cash collateral. ETNs are subject to credit risk. The value of an ETN may vary and may be influenced by time to maturity, level of supply and demand for the ETN, volatility and lack of liquidity in underlying commodities markets, changes in the applicable interest rates, changes in the issuer’s credit rating, and economic, legal, political, or geographic events that affect the referenced commodity. When an underlying fund invests in ETNs it will bear its proportionate share of any fees and expenses borne by the ETN. There may be restrictions on an underlying fund’s right to redeem its investment in an ETN, which is meant to be held until maturity. An underlying fund’s decision to sell its ETN holdings may be limited by the availability of a secondary market.

Derivatives Risk. Certain underlying funds may invest in derivatives. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

The biggest risk is that the Fund’s returns will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares, the initial share class) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund commenced operations on July 6, 2009.

• The performance shown for Class T Shares is calculated using the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class A Shares, Class C Shares, and Class S Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers.
• The performance shown for Class I Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers.

If Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund had been available during periods prior to July 6, 2009, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, and Class I Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. Performance information for each underlying fund is available in its prospectus and/or the most recent annual or semiannual report. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-877-335-2687

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/advisor/mutual-funds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class T Shares (calendar year-end)

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Second Quarter 2009  14.27%        Worst Quarter:  Fourth Quarter 2008  −11.62%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 10.26%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The Moderate Allocation Index is an internally-calculated, hypothetical combination of unmanaged indices that combines total returns from the Dow Jones Wilshire 5000 Index (40%), the Barclays U.S. Aggregate Bond Index (40%), the MSCI EAFE^® Index (18%), and the Morgan Stanley Capital International Emerging Markets Free Index^sm (2%).

After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares, the initial share class). After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Janus Moderate Allocation Fund | Class A, C, S, I, T Shares | Class A

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class A

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class A

Management Fees

rr_ManagementFeesOverAssets

0.05%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.15%

^[1]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.69%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.14%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleYear01

685

3 Years

rr_ExpenseExampleYear03

916

5 Years

rr_ExpenseExampleYear05

1,167

10 Years

rr_ExpenseExampleYear10

1,881

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

685

3 Years

rr_ExpenseExampleNoRedemptionYear03

916

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,167

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,881

Janus Moderate Allocation Fund | Class A, C, S, I, T Shares | Class C

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class C

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

1.00%

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class C

Management Fees

rr_ManagementFeesOverAssets

0.05%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

0.24%

^[1]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.69%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.98%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleYear01

301

3 Years

rr_ExpenseExampleYear03

621

5 Years

rr_ExpenseExampleYear05

1,068

10 Years

rr_ExpenseExampleYear10

2,306

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

201

3 Years

rr_ExpenseExampleNoRedemptionYear03

621

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,068

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,306

Janus Moderate Allocation Fund | Class A, C, S, I, T Shares | Class S

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class S

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class S

Management Fees

rr_ManagementFeesOverAssets

0.05%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.33%

^[1]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.69%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.32%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleYear01

134

3 Years

rr_ExpenseExampleYear03

418

5 Years

rr_ExpenseExampleYear05

723

10 Years

rr_ExpenseExampleYear10

1,590

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

134

3 Years

rr_ExpenseExampleNoRedemptionYear03

418

5 Years

rr_ExpenseExampleNoRedemptionYear05

723

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,590

Janus Moderate Allocation Fund | Class A, C, S, I, T Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class I

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class I

Management Fees

rr_ManagementFeesOverAssets

0.05%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.16%

^[1]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.69%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.90%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleYear01

92

3 Years

rr_ExpenseExampleYear03

287

5 Years

rr_ExpenseExampleYear05

498

10 Years

rr_ExpenseExampleYear10

1,108

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

92

3 Years

rr_ExpenseExampleNoRedemptionYear03

287

5 Years

rr_ExpenseExampleNoRedemptionYear05

498

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,108

Janus Moderate Allocation Fund | Class A, C, S, I, T Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class T

Management Fees

rr_ManagementFeesOverAssets

0.05%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.34%

^[1]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.69%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.08%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleYear01

110

3 Years

rr_ExpenseExampleYear03

343

5 Years

rr_ExpenseExampleYear05

595

10 Years

rr_ExpenseExampleYear10

1,317

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

110

3 Years

rr_ExpenseExampleNoRedemptionYear03

343

5 Years

rr_ExpenseExampleNoRedemptionYear05

595

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,317

2006

rr_AnnualReturn2006

14.28%

2007

rr_AnnualReturn2007

12.71%

2008

rr_AnnualReturn2008

(25.28%)

2009

rr_AnnualReturn2009

30.34%

2010

rr_AnnualReturn2010

12.19%

2011

rr_AnnualReturn2011

(2.61%)

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

10.26%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

14.27%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(11.62%)

Janus Moderate Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class A

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class A Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[2]

1 Year

rr_AverageAnnualReturnYear01

(8.26%)

5 Years

rr_AverageAnnualReturnYear05

2.33%

Since Inception

rr_AverageAnnualReturnSinceInception

4.19%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Moderate Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class C

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class C Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[3]

1 Year

rr_AverageAnnualReturnYear01

(4.34%)

5 Years

rr_AverageAnnualReturnYear05

2.80%

Since Inception

rr_AverageAnnualReturnSinceInception

4.46%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Moderate Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class S

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class S Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(2.93%)

5 Years

rr_AverageAnnualReturnYear05

3.30%

Since Inception

rr_AverageAnnualReturnSinceInception

4.97%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Moderate Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(2.47%)

5 Years

rr_AverageAnnualReturnYear05

3.70%

Since Inception

rr_AverageAnnualReturnSinceInception

5.39%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Moderate Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(2.61%)

5 Years

rr_AverageAnnualReturnYear05

3.70%

Since Inception

rr_AverageAnnualReturnSinceInception

5.39%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Moderate Allocation Fund | Class A, C, S, I, T Shares | Return After Taxes on Distributions | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

(3.32%)

5 Years

rr_AverageAnnualReturnYear05

2.81%

Since Inception

rr_AverageAnnualReturnSinceInception

4.55%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Moderate Allocation Fund | Class A, C, S, I, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[4]

1 Year

rr_AverageAnnualReturnYear01

(1.57%)

5 Years

rr_AverageAnnualReturnYear05

2.71%

Since Inception

rr_AverageAnnualReturnSinceInception

4.22%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Moderate Allocation Fund | Class A, C, S, I, T Shares | S&P 500 Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

S&P 500^® Index

1 Year

rr_AverageAnnualReturnYear01

2.11%

5 Years

rr_AverageAnnualReturnYear05

(0.25%)

Since Inception

rr_AverageAnnualReturnSinceInception

2.26%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

Janus Moderate Allocation Fund | Class A, C, S, I, T Shares | Moderate Allocation Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Moderate Allocation Index

1 Year

rr_AverageAnnualReturnYear01

0.96%

5 Years

rr_AverageAnnualReturnYear05

2.43%

Since Inception

rr_AverageAnnualReturnSinceInception

4.16%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

[1] Other Expenses are based on the estimated expenses that the Fund expects to incur.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

[4] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	JANUS INVESTMENT FUND
Prospectus Date	rr_ProspectusDate	Oct. 26, 2012
Perkins Small Cap Value Fund | Class A, C, S, I, N, R, T Shares
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Fund summary Perkins Small Cap Value Fund
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Perkins Small Cap Value Fund seeks capital appreciation.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE FUND
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	SHAREHOLDER FEES (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	November 1, 2013
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover:
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 62% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	62.00%
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the "Purchases" section on page 60 of the Fund's Prospectus and in the "Purchases" section on page 83 of the Fund's Statement of Additional Information.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	50,000
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE:
Expense Example by Year [Heading]	rr_ExpenseExampleByYearHeading	The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.
Expense Example by, Year, Caption [Text]	rr_ExpenseExampleByYearCaption	If Shares are redeemed:
Expense Example, No Redemption, By Year, Caption [Text]	rr_ExpenseExampleNoRedemptionByYearCaption	If Shares are not redeemed:
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Fund pursues its investment objective by investing primarily in the common stocks of small companies whose stock prices are believed to be undervalued by the Fund’s portfolio managers. The Fund invests, under normal circumstances, at least 80% of its net assets in equity securities of small companies whose market capitalization, at the time of initial purchase, is less than the 12-month average of the maximum market capitalization for companies included in the Russell 2000® Value Index. This average is updated monthly. The market capitalizations within the index will vary, but as of June 30, 2012, they ranged from approximately $85 million to $2.7 billion. The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets. The Fund may invest, under normal circumstances, up to 20% of its net assets in securities of companies having market capitalizations outside of the aforementioned market capitalization ranges. In addition, when the portfolio managers believe that market conditions are unfavorable for investing, or when they are otherwise unable to locate attractive investment opportunities, the Fund may invest up to 20% of its net assets in cash or similar investments. The Fund’s securities selection focuses on companies that are out of favor with markets or have not yet been discovered by the broader investment community. The Fund’s portfolio managers generally look for companies with: strong balance sheets and solid recurring free cash flows attractive relative and absolute valuation ratios or that have underperformed recently favorable reward to risk characteristics The portfolio managers’ philosophy is to weigh a security’s downside risk before considering its upside potential, which may help provide an element of capital preservation.
Risk [Heading]	rr_RiskHeading	PRINCIPAL INVESTMENT RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices. Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s portfolio managers. When the Fund’s investments in cash or similar investments increase due to a lack of favorable investment opportunities or other extraordinary factors, the Fund may not participate in market advances or declines to the same extent that it would if the Fund had been fully invested. Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money. Small-Sized Companies Risk. The Fund’s investments in securities issued by small-sized companies, which tend to be smaller, start-up companies offering emerging products or services, may involve greater risks than are customarily associated with larger, more established companies. Securities issued by small-sized companies tend to be more volatile and somewhat more speculative than securities issued by larger or more established companies and may underperform as compared to the securities of larger companies. Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Risk Lose Money [Text]	rr_RiskLoseMoney	The biggest risk is that the Fund’s returns will vary, and you could lose money.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	PERFORMANCE INFORMATION
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class R Shares of the Fund commenced operations on July 6, 2009. Class N Shares of the Fund commenced operations on May 31, 2012. The performance shown for Class T Shares for periods following April 21, 2003, reflects the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class T Shares reflects the historical performance of Berger Small Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Investor Shares into the Fund’s former Class J Shares). The performance shown for Class A Shares, Class C Shares, Class S Shares, and Class R Shares reflects the performance of the Fund’s Class J Shares (formerly named Investor Shares) from April 21, 2003 to July 6, 2009, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers. For periods prior to April 21, 2003, the performance shown for Class A Shares, Class C Shares, Class S Shares, and Class R Shares reflects the historical performance of Berger Small Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Investor Shares into the Fund’s former Class J Shares), calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers. The performance shown for Class I Shares reflects the performance of the Fund’s Class J Shares (formerly named Investor Shares) from April 21, 2003 to July 6, 2009, calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class I Shares reflects the historical performance of Berger Small Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Investor Shares into the Fund’s former Class J Shares), calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers. The performance shown for Class N Shares reflects the performance of the Fund’s Class T Shares from July 6, 2009 to December 31, 2011, calculated using the fees and expenses of Class T Shares, net of any applicable fee and expense limitations or waivers. For the period from April 21, 2003 to July 6, 2009, the performance shown for Class N Shares reflects the performance of the Fund’s Class J Shares (formerly named Investor Shares), calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class N Shares reflects the historical performance of Berger Small Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Investor Shares into the Fund’s former Class J Shares), calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers. If Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class R Shares of the Fund had been available during periods prior to July 6, 2009, or Class N Shares of the Fund had been available during periods prior to December 31, 2011, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, Class I Shares, Class N Shares, and Class R Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers. The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. The bar chart depicts the change in performance from year to year during the periods indicated.
Performance Additional Market Index [Text]	rr_PerformanceAdditionalMarketIndex	The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-877-335-2687
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	janus.com/advisor/mutual-funds
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Annual Total Returns for Class T Shares (calendar year-end)
Bar Chart Does Not Reflect Sales Loads [Text]	rr_BarChartDoesNotReflectSalesLoads	The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best Quarter:  Second Quarter 2009  23.04%          Worst Quarter:  Third Quarter 2002  −22.57%
Year to Date Return, Label	rr_YearToDateReturnLabel	The Fund's year-to-date return as of the calendar quarter ended September 30, 2012 was 6.24%.
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns (periods ended 12/31/11)
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.
Performance Table Explanation after Tax Higher	rr_PerformanceTableExplanationAfterTaxHigher	If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares) for the periods following April 21, 2003; and for Berger Small Cap Value Fund – Investor Shares for periods prior to April 21, 2003. If Class T Shares of the Fund had been available during the periods prior to April 21, 2003, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA. After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.
Performance Table Closing [Text Block]	rr_PerformanceTableClosingTextBlock	Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.
Perkins Small Cap Value Fund | Class A, C, S, I, N, R, T Shares | Class A
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	Class A
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	5.75%
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class A
Management Fees (may adjust up or down)	rr_ManagementFeesOverAssets	0.75%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.39%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.39%	[2]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	0.15%	[2]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.24%	[2]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class A Shares
1 Year	rr_ExpenseExampleYear01	708
3 Years	rr_ExpenseExampleYear03	990
5 Years	rr_ExpenseExampleYear05	1,292
10 Years	rr_ExpenseExampleYear10	2,148
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class A Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	708
3 Years	rr_ExpenseExampleNoRedemptionYear03	990
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,292
10 Years	rr_ExpenseExampleNoRedemptionYear10	2,148
Perkins Small Cap Value Fund | Class A, C, S, I, N, R, T Shares | Class C
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	Class C
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	1.00%
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class C
Management Fees (may adjust up or down)	rr_ManagementFeesOverAssets	0.75%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	0.30%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.05%	[2]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	0.06%	[2]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.99%	[2]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class C Shares
1 Year	rr_ExpenseExampleYear01	308
3 Years	rr_ExpenseExampleYear03	643
5 Years	rr_ExpenseExampleYear05	1,103
10 Years	rr_ExpenseExampleYear10	2,379
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class C Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	208
3 Years	rr_ExpenseExampleNoRedemptionYear03	643
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,103
10 Years	rr_ExpenseExampleNoRedemptionYear10	2,379
Perkins Small Cap Value Fund | Class A, C, S, I, N, R, T Shares | Class S
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	Class S
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class S
Management Fees (may adjust up or down)	rr_ManagementFeesOverAssets	0.75%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.29%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.29%	[2]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	none	[2]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.29%	[2]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class S Shares
1 Year	rr_ExpenseExampleYear01	131
3 Years	rr_ExpenseExampleYear03	409
5 Years	rr_ExpenseExampleYear05	708
10 Years	rr_ExpenseExampleYear10	1,556
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class S Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	131
3 Years	rr_ExpenseExampleNoRedemptionYear03	409
5 Years	rr_ExpenseExampleNoRedemptionYear05	708
10 Years	rr_ExpenseExampleNoRedemptionYear10	1,556
Perkins Small Cap Value Fund | Class A, C, S, I, N, R, T Shares | Class I
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	Class I
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class I
Management Fees (may adjust up or down)	rr_ManagementFeesOverAssets	0.75%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.14%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.89%	[2]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	none	[2]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	0.89%	[2]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class I Shares
1 Year	rr_ExpenseExampleYear01	91
3 Years	rr_ExpenseExampleYear03	284
5 Years	rr_ExpenseExampleYear05	493
10 Years	rr_ExpenseExampleYear10	1,096
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class I Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	91
3 Years	rr_ExpenseExampleNoRedemptionYear03	284
5 Years	rr_ExpenseExampleNoRedemptionYear05	493
10 Years	rr_ExpenseExampleNoRedemptionYear10	1,096
Perkins Small Cap Value Fund | Class A, C, S, I, N, R, T Shares | Class N
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	Class N
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class N
Management Fees (may adjust up or down)	rr_ManagementFeesOverAssets	0.75%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.04%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.79%	[2]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	none	[2]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	0.79%	[2]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class N Shares
1 Year	rr_ExpenseExampleYear01	81
3 Years	rr_ExpenseExampleYear03	252
5 Years	rr_ExpenseExampleYear05	439
10 Years	rr_ExpenseExampleYear10	978
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class N Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	81
3 Years	rr_ExpenseExampleNoRedemptionYear03	252
5 Years	rr_ExpenseExampleNoRedemptionYear05	439
10 Years	rr_ExpenseExampleNoRedemptionYear10	978
Perkins Small Cap Value Fund | Class A, C, S, I, N, R, T Shares | Class R
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	Class R
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class R
Management Fees (may adjust up or down)	rr_ManagementFeesOverAssets	0.75%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.50%
Other Expenses	rr_OtherExpensesOverAssets	0.29%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.54%	[2]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	none	[2]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.54%	[2]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class R Shares
1 Year	rr_ExpenseExampleYear01	157
3 Years	rr_ExpenseExampleYear03	486
5 Years	rr_ExpenseExampleYear05	839
10 Years	rr_ExpenseExampleYear10	1,834
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class R Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	157
3 Years	rr_ExpenseExampleNoRedemptionYear03	486
5 Years	rr_ExpenseExampleNoRedemptionYear05	839
10 Years	rr_ExpenseExampleNoRedemptionYear10	1,834
Perkins Small Cap Value Fund | Class A, C, S, I, N, R, T Shares | Class T
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	Class T
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class T
Management Fees (may adjust up or down)	rr_ManagementFeesOverAssets	0.75%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.30%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.05%	[2]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	none	[2]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.05%	[2]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class T Shares
1 Year	rr_ExpenseExampleYear01	107
3 Years	rr_ExpenseExampleYear03	334
5 Years	rr_ExpenseExampleYear05	579
10 Years	rr_ExpenseExampleYear10	1,283
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class T Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	107
3 Years	rr_ExpenseExampleNoRedemptionYear03	334
5 Years	rr_ExpenseExampleNoRedemptionYear05	579
10 Years	rr_ExpenseExampleNoRedemptionYear10	1,283
2002	rr_AnnualReturn2002	(15.59%)
2003	rr_AnnualReturn2003	36.78%
2004	rr_AnnualReturn2004	13.57%
2005	rr_AnnualReturn2005	8.90%
2006	rr_AnnualReturn2006	12.37%
2007	rr_AnnualReturn2007	2.97%
2008	rr_AnnualReturn2008	(21.79%)
2009	rr_AnnualReturn2009	36.59%
2010	rr_AnnualReturn2010	17.87%
2011	rr_AnnualReturn2011	(3.43%)
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	6.24%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	23.04%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2002
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(22.57%)
Perkins Small Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class A
Risk/Return:	rr_RiskReturnAbstract
Column	rr_AverageAnnualReturnColumnName	Class A Shares
Label	rr_AverageAnnualReturnLabel	Return Before Taxes	[3]
1 Year	rr_AverageAnnualReturnYear01	(9.12%)
5 Years	rr_AverageAnnualReturnYear05	3.17%
10 Years	rr_AverageAnnualReturnYear10	6.34%
Perkins Small Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class C
Risk/Return:	rr_RiskReturnAbstract
Column	rr_AverageAnnualReturnColumnName	Class C Shares
Label	rr_AverageAnnualReturnLabel	Return Before Taxes	[4]
1 Year	rr_AverageAnnualReturnYear01	(5.21%)
5 Years	rr_AverageAnnualReturnYear05	3.62%
10 Years	rr_AverageAnnualReturnYear10	6.22%
Perkins Small Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class S
Risk/Return:	rr_RiskReturnAbstract
Column	rr_AverageAnnualReturnColumnName	Class S Shares
Label	rr_AverageAnnualReturnLabel	Return Before Taxes
1 Year	rr_AverageAnnualReturnYear01	(3.69%)
5 Years	rr_AverageAnnualReturnYear05	4.36%
10 Years	rr_AverageAnnualReturnYear10	6.98%
Perkins Small Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class I
Risk/Return:	rr_RiskReturnAbstract
Column	rr_AverageAnnualReturnColumnName	Class I Shares
Label	rr_AverageAnnualReturnLabel	Return Before Taxes
1 Year	rr_AverageAnnualReturnYear01	(3.28%)
5 Years	rr_AverageAnnualReturnYear05	4.60%
10 Years	rr_AverageAnnualReturnYear10	7.23%
Perkins Small Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class N
Risk/Return:	rr_RiskReturnAbstract
Column	rr_AverageAnnualReturnColumnName	Class N Shares
Label	rr_AverageAnnualReturnLabel	Return Before Taxes
1 Year	rr_AverageAnnualReturnYear01	(3.43%)
5 Years	rr_AverageAnnualReturnYear05	4.60%
10 Years	rr_AverageAnnualReturnYear10	7.23%
Perkins Small Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class R
Risk/Return:	rr_RiskReturnAbstract
Column	rr_AverageAnnualReturnColumnName	Class R Shares
Label	rr_AverageAnnualReturnLabel	Return Before Taxes
1 Year	rr_AverageAnnualReturnYear01	(3.89%)
5 Years	rr_AverageAnnualReturnYear05	4.10%
10 Years	rr_AverageAnnualReturnYear10	6.72%
Perkins Small Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return Before Taxes | Class T
Risk/Return:	rr_RiskReturnAbstract
Column	rr_AverageAnnualReturnColumnName	Class T Shares
Label	rr_AverageAnnualReturnLabel	Return Before Taxes
1 Year	rr_AverageAnnualReturnYear01	(3.43%)
5 Years	rr_AverageAnnualReturnYear05	4.60%
10 Years	rr_AverageAnnualReturnYear10	7.23%
Perkins Small Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return After Taxes on Distributions | Class T
Risk/Return:	rr_RiskReturnAbstract
Column	rr_AverageAnnualReturnColumnName	Class T Shares
Label	rr_AverageAnnualReturnLabel	Return After Taxes on Distributions
1 Year	rr_AverageAnnualReturnYear01	(5.87%)
5 Years	rr_AverageAnnualReturnYear05	2.87%
10 Years	rr_AverageAnnualReturnYear10	5.36%
Perkins Small Cap Value Fund | Class A, C, S, I, N, R, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class T
Risk/Return:	rr_RiskReturnAbstract
Column	rr_AverageAnnualReturnColumnName	Class T Shares
Label	rr_AverageAnnualReturnLabel	Return After Taxes on Distributions and Sale of Fund Shares	[5]
1 Year	rr_AverageAnnualReturnYear01	(0.57%)
5 Years	rr_AverageAnnualReturnYear05	3.41%
10 Years	rr_AverageAnnualReturnYear10	5.73%
Perkins Small Cap Value Fund | Class A, C, S, I, N, R, T Shares | Russell 2000 Value Index (reflects no deduction for expenses, fees, or taxes)
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Russell 2000® Value Index
1 Year	rr_AverageAnnualReturnYear01	(5.50%)
5 Years	rr_AverageAnnualReturnYear05	(1.87%)
10 Years	rr_AverageAnnualReturnYear10	6.40%

[1] Other Expenses for Class N Shares are based on the estimated expenses that the Shares expect to incur during their initial fiscal period.

[2] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding any performance adjustments to management fees, the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, Class S Shares, and Class R Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 0.96% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

[3] Calculated assuming maximum permitted sales loads.

[4] The one year return is calculated to include the contingent deferred sales charge.

[5] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

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Perkins Select Value Fund | Class A, C, S, I, N, T Shares

Fund summary

Perkins Select Value Fund

INVESTMENT OBJECTIVE

Perkins Select Value Fund seeks capital appreciation.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 60 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.

SHAREHOLDER FEES
(fees paid directly from your investment)

Shareholder Fees Perkins Select Value Fund Class A, C, S, I, N, T Shares	Class A	Class C	Class S	Class I	Class N	Class T
Shareholder Fees Column [Text]	Class A	Class C	Class S	Class I	Class N	Class T
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	5.75%	none	none	none	none	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	none	1.00%	none	none	none	none

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Perkins Select Value Fund Class A, C, S, I, N, T Shares		Class A	Class C	Class S	Class I	Class N		Class T
Operating Expenses Column [Text]		Class A	Class C	Class S	Class I	Class N		Class T
Management Fees (may adjust up or down)		0.70%	0.70%	0.70%	0.70%	0.70%		0.70%
Distribution/Service (12b-1) Fees		0.25%	1.00%	0.25%	none	none		none
Other Expenses		0.56%	0.73%	0.78%	0.56%	0.56%	[1]	0.74%
Total Annual Fund Operating Expenses	[2]	1.51%	2.43%	1.73%	1.26%	1.26%		1.44%
Fee Waiver	[2]	0.24%	0.41%	0.21%	0.24%	0.24%		0.17%
Total Annual Fund Operating Expenses After Fee Waiver	[2]	1.27%	2.02%	1.52%	1.02%	1.02%		1.27%

EXAMPLE:

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

If Shares are redeemed:

Expense Example Perkins Select Value Fund Class A, C, S, I, N, T Shares (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	720	1,025	1,351	2,273
Class C	Class C Shares	346	758	1,296	2,766
Class S	Class S Shares	176	545	939	2,041
Class I	Class I Shares	128	400	692	1,523
Class N	Class N Shares	128	400	692	1,523
Class T	Class T Shares	147	456	787	1,724

If Shares are not redeemed:

Expense Example, No Redemption Perkins Select Value Fund Class A, C, S, I, N, T Shares (USD $)	Expense Example, No Redemption, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	720	1,025	1,351	2,273
Class C	Class C Shares	246	758	1,296	2,766
Class S	Class S Shares	176	545	939	2,041
Class I	Class I Shares	128	400	692	1,523
Class N	Class N Shares	128	400	692	1,523
Class T	Class T Shares	147	456	787	1,724

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the period December 15, 2011 to June 30, 2012, the Fund’s portfolio turnover rate was 80% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objective by investing primarily in common stocks selected for their capital appreciation potential. The Fund primarily invests in the common stocks of companies of any size whose stock prices the portfolio managers believe to be undervalued. The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets. In addition, when the portfolio managers believe that market conditions are unfavorable for investing, or when they are otherwise unable to locate attractive investment opportunities, the Fund’s cash or similar investments may increase.

The Fund focuses on companies that have fallen out of favor with the market or that appear to be temporarily misunderstood by the investment community. The Fund’s portfolio managers generally look for companies with:

• strong balance sheets and solid recurring free cash flows
• attractive relative and absolute valuation ratios or that have underperformed recently
• favorable reward to risk characteristics

The Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices, as substitutes for securities in which the Fund invests. The Fund may invest in derivative instruments (by taking long and/or short positions) for different purposes, including hedging (to offset risks associated with an investment, currency exposure, or market conditions) and to earn income and enhance returns. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s portfolio managers. When the Fund’s investments in cash or similar investments increase due to a lack of favorable investment opportunities or other extraordinary factors, the Fund may not participate in market advances or declines to the same extent that it would if the Fund had been fully invested.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The Fund does not have a full calendar year of operations. Performance information for certain periods is included in the Fund’s first annual and/or semiannual report.

[1] Other Expenses for Class N Shares are based on the estimated expenses that the Shares expect to incur during their initial fiscal period.

[2] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding any performance adjustments to management fees, the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, and Class S Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 1.00% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

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Perkins Value Plus Income Fund | Class D Shares

Fund summary

Perkins Value Plus Income Fund

INVESTMENT OBJECTIVE

Perkins Value Plus Income Fund seeks capital appreciation and current income.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses		Perkins Value Plus Income Fund Class D Shares Class D
Operating Expenses Column [Text]		Class D
Management Fees		0.60%
Other Expenses		0.81%
Total Annual Fund Operating Expenses	[1]	1.41%
Fee Waiver	[1]	0.50%
Total Annual Fund Operating Expenses After Fee Waiver	[1]	0.91%

EXAMPLE:

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers or recoupments (if applicable) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Perkins Value Plus Income Fund Class D Shares Class D	Class D Shares	144	446	771	1,691

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 100% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objective by normally investing 40-60% of its assets in equity securities selected primarily for capital appreciation and investing the remainder in fixed-income securities and cash equivalents.

Equity Securities. The Fund’s equity investments generate total return from a combination of capital appreciation and, to a lesser degree, current income. Such equity investments may include companies of any size, but the Fund will invest primarily in large- and mid-sized companies whose stock prices the portfolio managers believe to be undervalued or have the potential for high relative dividend yields, or both. The Fund’s equity portfolio managers invest in companies which have fallen out of favor with the market or that appear to be temporarily misunderstood by the investment community. The Fund’s equity portfolio managers generally look for companies with:

• strong balance sheets and solid recurring free cash flows
• attractive relative and absolute valuation ratios or that have underperformed recently
• favorable reward to risk characteristics

Fixed-Income Securities. The Fund’s fixed-income investments generate total return from a combination of current income and capital appreciation, but income is usually the dominant portion. The Fund normally invests the portion of its assets allocated to fixed-income investments in debt securities (including, but not limited to, government bonds, corporate bonds, mortgage-backed securities, asset-backed securities, zero-coupon bonds, and bank loans), convertible securities, and short-term securities. The Fund invests at least 50% of the fixed-income portion of its assets in investment grade debt securities. The Fund will limit its investment in high-yield/high-risk bonds, also known as “junk” bonds, to 50% or less of the fixed-income portion of its net assets.

In addition to considering economic factors such as the effect of interest rates on the Fund’s fixed-income investments, the Fund’s fixed-income portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income-producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets.

The Fund may also invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. The Fund has and is expected to continue to buy and sell put and call options to enhance returns. The Fund’s exposure to derivatives will vary, is not limited to those derivatives listed, and could be significant at times. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

Janus Capital is primarily responsible for the overall asset allocation of the Fund and manages the Fund’s fixed-income investments. Cash positions are considered a part of the Fund’s fixed-income allocation and will be managed by the Fund’s fixed-income portfolio managers. Perkins manages the Fund’s equity investments and assists the adviser in determining the Fund’s overall asset allocation. The Fund may periodically adjust its mix of equity and fixed-income investments in response to changing economic and market conditions, including outside the range of 40-60% of its assets in equity securities. Due to the nature of the fixed-income securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns and yields will vary, and you could lose money. The Fund is designed for long-term investors seeking a portfolio including common stocks and bonds selected for their potential to produce capital appreciation and current income. Common stocks tend to be more volatile than many other investment choices.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s equity portfolio managers.

Mid-Sized Companies Risk. The Fund’s investments in securities issued by mid-sized companies may involve greater risks than are customarily associated with larger, more established companies. Securities issued by mid-sized companies tend to be more volatile than securities issued by larger or more established companies and may underperform as compared to the securities of larger companies.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

High-Yield/High-Risk Bond Risk. High-yield/high-risk bonds may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Bank Loan Risk. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. Participation interests and assignments involve credit, interest rate, and liquidity risk. In addition, the bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

Foreign Exposure Risk. The Fund may have significant exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited.

Allocation Risk. The Fund’s ability to achieve its investment objective depends largely upon the allocation of assets among the equity and fixed asset categories. You could lose money on your investment in the Fund as a result of these allocations. Portfolio management may favor an asset category that underperforms relative to other asset categories. For example, the Fund may be overweighted in equity securities when the stock market is falling and the fixed-income market is rising. Additionally, periodic rebalancing of Fund assets among asset categories may result in increased transaction costs, which may have a negative effect on the Fund’s performance.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. The bar chart depicts the Fund’s performance during the period indicated. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Annual Total Returns for Class D Shares (calendar year-end)

Best Quarter:  Fourth Quarter 2011  7.30%        Worst Quarter:  Third Quarter 2011  −7.84%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 10.38%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Perkins Value Plus Income Fund Class D Shares	Column	Label		1 Year	Since Inception	Inception Date
Class D Return Before Taxes	Class D Shares	Return Before Taxes		3.66%	9.21%	Jul. 30, 2010
Class D Return After Taxes on Distributions	Class D Shares	Return After Taxes on Distributions		1.61%	7.38%	Jul. 30, 2010
Class D Return After Taxes on Distributions and Sale of Fund Shares	Class D Shares	Return After Taxes on Distributions and Sale of Fund Shares	[1]	2.68%	6.92%	Jul. 30, 2010
Russell 1000 Value Index (reflects no deduction for expenses, fees, or taxes)		Russell 1000® Value Index		0.39%	9.97%	Jul. 30, 2010
Barclays U.S. Aggregate Bond Index (reflects no deduction for expenses, fees, or taxes)		Barclays U.S. Aggregate Bond Index		7.84%	5.51%	Jul. 30, 2010
Value Income Index (reflects no deduction for expenses, fees, or taxes)		Value Income Index		4.44%	8.16%	Jul. 30, 2010

The Value Income Index is an internally-calculated, hypothetical combination of unmanaged indices that combines total returns from the Russell 1000^® Value Index (50%) and the Barclays U.S. Aggregate Bond Index (50%).

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding administrative services fees payable pursuant to the Transfer Agency Agreement, brokerage commissions, interest, dividends, taxes, acquired fund fees and expenses, and extraordinary expenses) to 0.76% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees. For a period of three years subsequent to the Fund's commencement of operations (July 30, 2010), Janus Capital may recover from the Fund fees and expenses previously waived or reimbursed, which could then be considered a deferral, if the Fund's expense ratio, including recovered expenses, falls below the expense limit.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

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Document and Entity Information	12 Months Ended
	Oct. 26, 2012
Risk/Return:
Document Type	485BPOS
Document Period End Date	Jun. 30, 2012
Registrant Name	JANUS INVESTMENT FUND
Central Index Key	0000277751
Amendment Flag	false
Document Creation Date	Oct. 25, 2012
Document Effective Date	Oct. 26, 2012
Prospectus Date	Oct. 26, 2012

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Janus Growth Allocation Fund | Class A, C, S, I, T Shares

Fund summary

Janus Growth Allocation Fund

INVESTMENT OBJECTIVE

Janus Growth Allocation Fund seeks total return through a primary emphasis on growth of capital with a secondary emphasis on income.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 45 of the Fund’s Prospectus and in the “Purchases” section on page 63 of the Fund’s Statement of Additional Information.

SHAREHOLDER FEES
(fees paid directly from your investment)

Shareholder Fees Janus Growth Allocation Fund Class A, C, S, I, T Shares	Class A	Class C	Class S	Class I	Class T
Shareholder Fees Column [Text]	Class A	Class C	Class S	Class I	Class T
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	5.75%	none	none	none	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	none	1.00%	none	none	none

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Janus Growth Allocation Fund Class A, C, S, I, T Shares		Class A	Class C	Class S	Class I	Class T
Operating Expenses Column [Text]		Class A	Class C	Class S	Class I	Class T
Management Fees		0.05%	0.05%	0.05%	0.05%	0.05%
Distribution/Service (12b-1) Fees		0.25%	1.00%	0.25%	none	none
Other Expenses	[1]	0.22%	0.33%	0.36%	0.20%	0.37%
Acquired Fund Fees and Expenses		0.76%	0.76%	0.76%	0.76%	0.76%
Total Annual Fund Operating Expenses		1.28%	2.14%	1.42%	1.01%	1.18%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses (including the operating expenses of the underlying funds) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

If Shares are redeemed:

Expense Example Janus Growth Allocation Fund Class A, C, S, I, T Shares (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	698	958	1,237	2,031
Class C	Class C Shares	317	670	1,149	2,472
Class S	Class S Shares	145	449	776	1,702
Class I	Class I Shares	103	322	558	1,236
Class T	Class T Shares	120	375	649	1,432

If Shares are not redeemed:

Expense Example, No Redemption Janus Growth Allocation Fund Class A, C, S, I, T Shares (USD $)	Expense Example, No Redemption, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	698	958	1,237	2,031
Class C	Class C Shares	217	670	1,149	2,472
Class S	Class S Shares	145	449	776	1,702
Class I	Class I Shares	103	322	558	1,236
Class T	Class T Shares	120	375	649	1,432

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 18% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund seeks to achieve its investment objective by investing in other Janus mutual funds (“underlying funds”) that represent a variety of asset classes and investment styles. The Fund pursues this objective by investing in a diversified portfolio of underlying funds resulting in an allocation of the Fund’s investments that normally provides exposure of approximately 80% to stocks and 20% to bonds and money market securities. The target allocation and the allocation of the Fund’s assets among underlying funds are based on quantitative and qualitative analysis. Because it invests in other funds, the Fund is considered a “fund of funds.”

The Fund’s asset allocation is intended to diversify investments among stocks, bonds, and cash equivalents. The portfolio manager regularly reviews the allocation of Fund assets in the underlying funds and may modify the underlying funds’ weightings or substitute other underlying funds to emphasize and mitigate risk exposures that may arise as a result of the implementation of the allocations. An independent asset allocation service provides evaluations of asset allocations that the portfolio manager may use in implementing the allocations among the underlying funds. The portfolio manager continually monitors asset class allocations and periodically rebalances the Fund’s investments in the underlying funds. The portfolio manager may change the Fund’s asset class allocations, the underlying funds, an underlying fund’s asset category, or weightings among asset classes or underlying funds without prior shareholder notice.

The Fund will normally allocate approximately 80% of its investments to underlying funds that provide varying exposure to common stocks of large U.S.-based companies, small- to mid-capitalization companies, and international companies (including those with exposure to emerging markets); and approximately 20% of its investments to underlying bond funds and money market instruments. Refer to Appendix A in this Prospectus for a brief description of the investment strategies of each of the currently available underlying funds.

When market conditions dictate a more defensive strategy, the Fund or an underlying fund may temporarily hold cash or invest its assets in temporary investments. In that case, the Fund may take positions that are inconsistent with its investment objective. As a result, the Fund may not achieve its investment objective.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking growth of capital and, to a lesser extent, income. Investments in a portfolio with common stock exposure tend to be more volatile than many other investment choices.

Main Risks Associated with the Fund
Allocation Risk. The Fund’s ability to achieve its investment objective depends largely upon the portfolio manager’s allocation of assets among the underlying funds and other securities, using the optimization process (a process that utilizes quantitative analysis of a number of factors, such as historical risk, performance, fund classifications, and the relationship among underlying funds) and the judgment of the portfolio manager. You could lose money on your investment in the Fund as a result of these allocations. The Fund will typically invest in a number of different underlying funds; however, to the extent that the Fund invests a significant portion of its assets in a single underlying fund, it will be more sensitive to the risks associated with that fund and any investments in which that fund concentrates.

Affiliated Fund Risk. Janus Capital has the authority to select and substitute underlying affiliated mutual funds. The fees paid to Janus Capital by some Janus mutual funds are generally higher than the fees paid to Janus Capital by the Fund or by other funds and share classes available for investment by the Fund. These conditions may create a conflict of interest when selecting underlying affiliated mutual funds and share classes for investment. Janus Capital, however, is a fiduciary to the Fund and its shareholders and is legally obligated to act in their best interest when selecting underlying affiliated mutual funds.

Main Risks Associated with the Underlying Funds and Securities
The biggest risk is that the underlying funds’ returns will vary, and you could lose money.

Market Risk. Approximately 80% of the Fund’s assets are allocated to equity investments through investments in underlying funds. The value of an underlying fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if a portfolio manager’s belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of an underlying fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Fixed-Income Securities Risk. Approximately 20% of the Fund’s assets are allocated to fixed-income securities through investments in underlying funds. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause an underlying fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which an underlying fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that an underlying fund’s portfolio manager would like or at the price that the portfolio manager believes the security is currently worth.

Foreign Exposure Risk. Certain underlying funds may have significant exposure to foreign markets as a result of their investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, an underlying fund’s returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. A market swing in one or more countries or regions where an underlying fund has invested a significant amount of its assets may have a greater effect on an underlying fund’s performance than it would in a more geographically diversified portfolio. An underlying fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Emerging Markets Risk. The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities involve a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. In addition, an underlying fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of an underlying fund’s investments. To the extent that an underlying fund invests a significant portion of its assets in the securities of issuers in or companies of a single country or region, it is more likely to be impacted by events or conditions affecting that country or region, which could have a negative impact on the Fund’s performance. Some of the risks of investing directly in foreign and emerging market securities may be reduced when an underlying fund invests indirectly in foreign securities through various other investment vehicles including derivatives, which also involve other risks.

Sovereign Debt Risk. An underlying fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Exchange-Traded Funds Risk. Certain underlying funds may purchase shares of exchange-traded funds (“ETFs”) to gain exposure to a particular portion of the market. ETFs are pooled investment vehicles, which may be managed or unmanaged, that generally seek to track the performance of a specific index. ETFs are traded on an exchange at market prices that may vary from the net asset value of their underlying investments. When an underlying fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF’s expenses. ETFs have certain inherent risks generally associated with investments in a portfolio of securities in which the ETF is invested, including the risk that the general level of stock prices may decline, thereby adversely affecting the value of each unit of the ETF. ETFs also involve the risk that an active trading market for an ETF’s shares may not develop or be maintained.

Exchange-Traded Notes Risk. Certain underlying funds may invest in exchange-traded notes (“ETNs”), which are debt securities whose returns are linked to a particular index. ETNs are typically linked to the performance of a commodities index that reflects the potential return on unleveraged investments in futures contracts of physical commodities, plus a specified rate of interest that could be earned on cash collateral. ETNs are subject to credit risk. The value of an ETN may vary and may be influenced by time to maturity, level of supply and demand for the ETN, volatility and lack of liquidity in underlying commodities markets, changes in the applicable interest rates, changes in the issuer’s credit rating, and economic, legal, political, or geographic events that affect the referenced commodity. When an underlying fund invests in ETNs it will bear its proportionate share of any fees and expenses borne by the ETN. There may be restrictions on an underlying fund’s right to redeem its investment in an ETN, which is meant to be held until maturity. An underlying fund’s decision to sell its ETN holdings may be limited by the availability of a secondary market.

Derivatives Risk. Certain underlying funds may invest in derivatives. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares, the initial share class) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund commenced operations on July 6, 2009.

• The performance shown for Class T Shares is calculated using the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class A Shares, Class C Shares, and Class S Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers.
• The performance shown for Class I Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers.

If Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund had been available during periods prior to July 6, 2009, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, and Class I Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. Performance information for each underlying fund is available in its prospectus and/or the most recent annual or semiannual report. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Annual Total Returns for Class T Shares (calendar year-end)

Best Quarter:  Second Quarter 2009  18.37%          Worst Quarter:  Fourth Quarter 2008  −18.05%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 11.44%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Janus Growth Allocation Fund Class A, C, S, I, T Shares	Column	Label		1 Year	5 Years	Since Inception	Inception Date
Class T Shares Return Before Taxes	Class T Shares	Return Before Taxes		(6.49%)	1.64%	4.27%	Dec. 30, 2005
Class T Shares Return After Taxes on Distributions	Class T Shares	Return After Taxes on Distributions		(6.91%)	1.01%	3.66%	Dec. 30, 2005
Class T Shares Return After Taxes on Distributions and Sale of Fund Shares	Class T Shares	Return After Taxes on Distributions and Sale of Fund Shares	[1]	(4.07%)	1.13%	3.42%	Dec. 30, 2005
Class A Shares Return Before Taxes	Class A Shares	Return Before Taxes	[2]	(11.93%)	0.30%	3.10%	Dec. 30, 2005
Class C Shares Return Before Taxes	Class C Shares	Return Before Taxes	[3]	(8.17%)	0.75%	3.35%	Dec. 30, 2005
Class S Shares Return Before Taxes	Class S Shares	Return Before Taxes		(6.79%)	1.27%	3.88%	Dec. 30, 2005
Class I Shares Return Before Taxes	Class I Shares	Return Before Taxes		(6.38%)	1.64%	4.27%	Dec. 30, 2005
S&P 500 Index (reflects no deduction for expenses, fees, or taxes)		S&P 500® Index		2.11%	(0.25%)	2.26%	Dec. 30, 2005
Growth Allocation Index (reflects no deduction for expenses, fees, or taxes)		Growth Allocation Index		(2.07%)	0.80%	3.31%	Dec. 30, 2005

The Growth Allocation Index is an internally-calculated, hypothetical combination of unmanaged indices that combines total returns from the Dow Jones Wilshire 5000 Index (50%), the MSCI EAFE^® Index (25%), the Barclays U.S. Aggregate Bond Index (20%), and the Morgan Stanley Capital International Emerging Markets Free Index^sm (5%).

After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares, the initial share class). After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

[1] Other Expenses are based on the estimated expenses that the Fund expects to incur.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

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INTECH U.S. Core Fund | Class D Shares

Fund summary

INTECH U.S. Core Fund

INVESTMENT OBJECTIVE

INTECH U.S. Core Fund seeks long-term growth of capital.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses

INTECH U.S. Core Fund

Class D Shares

Class D

Operating Expenses Column [Text]

Class D

Management Fees (may adjust up or down)

0.54%

Other Expenses

0.30%

Total Annual Fund Operating Expenses

0.84%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)

Expense Example, By Year, Column [Text]

1 Year

3 Years

5 Years

10 Years

INTECH U.S. Core Fund Class D Shares Class D

Class D Shares

86

268

466

1,037

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 73% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund invests, under normal circumstances, at least 80% of its net assets in U.S. common stocks from the universe of the S&P 500^® Index, utilizing INTECH’s mathematical investment process. The S&P 500^® Index is an unmanaged index of 500 stocks that is generally representative of the performance of larger companies in the United States.

The Fund pursues its investment objective by applying a mathematical investment process to construct an investment portfolio from the universe of common stocks within its named benchmark index. The goal of this process is to build a portfolio of stocks in a more efficient combination than the named benchmark index. The process seeks to capitalize on the natural volatility of the market by searching for stocks within the index that have high relative volatility (providing the potential for excess returns) but that essentially move in opposite directions or have low correlation to each other (providing the potential for lower relative risk). By constructing the portfolio in this manner and periodically rebalancing the portfolio to maintain potentially more efficient weightings, INTECH’s mathematical investment process seeks to create a portfolio that, over time, produces returns in excess of its named benchmark index with risks similar to that of the benchmark index. The rebalancing techniques used by INTECH may result in a higher portfolio turnover compared to a “buy and hold” fund strategy.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Investment Process Risk. The proprietary mathematical investment process used by INTECH may not achieve the desired results. On an occasional basis, INTECH considers changes to its mathematical investment process. These changes may result in changes to the portfolio, might not provide the intended results, and may adversely impact the Fund’s performance.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares, the predecessor share class. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses in effect during the periods shown, net of any applicable fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Annual Total Returns for Class D Shares (calendar year-end)

Best Quarter:  Second Quarter 2009  14.79%        Worst Quarter:  Fourth Quarter 2008 -21.49%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 14.92%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns INTECH U.S. Core Fund Class D Shares

Column

Label

1 Year

5 Years

Since Inception

Inception Date

Class D Return Before Taxes

Class D Shares

Return Before Taxes

5.07%

0.29%

7.81%

Feb. 28, 2003

Class D Return After Taxes on Distributions

Class D Shares

Return After Taxes on Distributions

4.92%

(0.20%)

7.08%

Feb. 28, 2003

Class D Return After Taxes on Distributions and Sale of Fund Shares

Class D Shares

Return After Taxes on Distributions and Sale of Fund Shares

^[1]

3.50%

0.21%

6.74%

Feb. 28, 2003

S&P 500 Index (reflects no deduction for expenses, fees, or taxes)

S&P 500® Index

2.11%

(0.25%)

6.77%

Feb. 28, 2003

After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; and for the Fund’s Class J Shares, the predecessor share class, for the periods prior to February 16, 2010. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Perkins Mid Cap Value Fund | Class L Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Perkins Mid Cap Value Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Perkins Mid Cap Value Fund seeks capital appreciation.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 54% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

54.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund pursues its investment objective by investing primarily in common stocks selected for their capital appreciation potential. The Fund primarily invests in the common stocks of mid-sized companies whose stock prices the portfolio managers believe to be undervalued. The Fund invests, under normal circumstances, at least 80% of its net assets in equity securities of companies whose market capitalization falls, at the time of purchase, within the 12-month average of the capitalization range of the Russell Midcap® Value Index. This average is updated monthly. The market capitalizations within the index will vary, but as of June 30, 2012, they ranged from approximately $1.3 billion to $18.5 billion. The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets. The Fund may invest, under normal circumstances, up to 20% of its net assets in securities of companies having market capitalizations outside of the aforementioned market capitalization ranges. In addition, when the portfolio managers believe that market conditions are unfavorable for investing, or when they are otherwise unable to locate attractive investment opportunities, the Fund may invest up to 20% of its net assets in cash or similar investments.

The Fund focuses on companies that have fallen out of favor with the market or that appear to be temporarily misunderstood by the investment community. The Fund’s portfolio managers generally look for companies with:

• strong balance sheets and solid recurring free cash flows
• attractive relative and absolute valuation ratios or that have underperformed recently
• favorable reward to risk characteristics

The Fund may also invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. The Fund has and is expected to continue to buy and sell put and call options, particularly on market indices, for hedging purposes (to offset risks associated with an investment, currency exposure, or market conditions) and to enhance returns. The Fund’s exposure to derivatives will vary, is not limited to those derivatives listed, and could be significant at times. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s portfolio managers. When the Fund’s investments in cash or similar investments increase due to a lack of favorable investment opportunities or other extraordinary factors, the Fund may not participate in market advances or declines to the same extent that it would if the Fund had been fully invested.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Mid-Sized Companies Risk. The Fund’s investments in securities issued by mid-sized companies may involve greater risks than are customarily associated with larger, more established companies. Securities issued by mid-sized companies tend to be more volatile than securities issued by larger or more established companies and may underperform as compared to the securities of larger companies.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

The biggest risk is that the Fund’s returns will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. The performance shown for periods following April 21, 2003, reflects the fees and expenses of Class L Shares (formerly named Institutional Shares), net of any applicable fee and expense limitations or waivers. The performance shown for Class L Shares for the periods from May 17, 2002 to April 17, 2003, reflects the historical performance of Berger Mid Cap Value Fund – Institutional Shares (as a result of a prior reorganization of Berger Mid Cap Value Fund – Institutional Shares into the Fund’s Class L Shares). For the periods prior to May 17, 2002, the performance shown reflects the historical performance of Berger Mid Cap Value Fund – Investor Shares.

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-877-335-2687

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/advisor/mutual-funds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class L Shares (calendar year-end)

^[1]

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Second Quarter 2003  17.19%          Worst Quarter:  Fourth Quarter 2008  −19.56%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 9.05%.

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

After-tax returns are calculated using distributions for the Fund’s Class L Shares (formerly named Institutional Shares) for the periods following April 21, 2003 for Berger Mid Cap Value Fund – Institutional Shares for the period May 17, 2002 to April 17, 2003; and for Berger Mid Cap Value Fund – Investor Shares for periods prior to May 17, 2002. If Class L Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Caption

rr_AverageAnnualReturnCaption

Average Annual Total Returns (periods ended 12/31/11)

^[1]

Perkins Mid Cap Value Fund | Class L Shares | Class L

Risk/Return:

rr_RiskReturnAbstract

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class L

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.54%

Other Expenses

rr_OtherExpensesOverAssets

0.30%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.84%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class L Shares

1 Year

rr_ExpenseExampleYear01

86

3 Years

rr_ExpenseExampleYear03

268

5 Years

rr_ExpenseExampleYear05

466

10 Years

rr_ExpenseExampleYear10

1,037

2002

rr_AnnualReturn2002

(12.95%)

2003

rr_AnnualReturn2003

39.77%

2004

rr_AnnualReturn2004

18.56%

2005

rr_AnnualReturn2005

10.53%

2006

rr_AnnualReturn2006

15.42%

2007

rr_AnnualReturn2007

7.56%

2008

rr_AnnualReturn2008

(27.19%)

2009

rr_AnnualReturn2009

30.74%

2010

rr_AnnualReturn2010

15.01%

2011

rr_AnnualReturn2011

(2.33%)

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

9.05%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:  

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2003

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

17.19%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:  

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(19.56%)

Perkins Mid Cap Value Fund | Class L Shares | Return Before Taxes | Class L

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class L Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(2.33%)

5 Years

rr_AverageAnnualReturnYear05

2.84%

10 Years

rr_AverageAnnualReturnYear10

7.79%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

11.92%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 12, 1998

Perkins Mid Cap Value Fund | Class L Shares | Return After Taxes on Distributions | Class L

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class L Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

(3.70%)

5 Years

rr_AverageAnnualReturnYear05

1.81%

10 Years

rr_AverageAnnualReturnYear10

6.66%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

10.45%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 12, 1998

Perkins Mid Cap Value Fund | Class L Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class L

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class L Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[2]

1 Year

rr_AverageAnnualReturnYear01

(0.03%)

5 Years

rr_AverageAnnualReturnYear05

2.21%

10 Years

rr_AverageAnnualReturnYear10

6.51%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

10.08%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 12, 1998

Perkins Mid Cap Value Fund | Class L Shares | Russell Midcap Value Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Russell Midcap® Value Index

1 Year

rr_AverageAnnualReturnYear01

(1.38%)

5 Years

rr_AverageAnnualReturnYear05

0.04%

10 Years

rr_AverageAnnualReturnYear10

7.67%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

7.70%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 12, 1998

[1] Fund returns for periods prior to the Fund's adoption of share classes reflect a 0.25% 12b-1 fee, which has not been paid by the Class L Shares (formerly named Institutional Shares) since the class commenced investment operations on May 17, 2002.

[2] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

INTECH U.S. Growth Fund | Class A, C, S, I, T Shares

Fund summary

INTECH U.S. Growth Fund

INVESTMENT OBJECTIVE

INTECH U.S. Growth Fund seeks long-term growth of capital.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the "Purchases" section on page 46 of the Fund's Prospectus and in the "Purchases" section on page 83 of the Fund's Statement of Additional Information.

SHAREHOLDER FEES
(fees paid directly from your investment)

Shareholder Fees INTECH U.S. Growth Fund Class A, C, S, I, T Shares	Class A	Class C	Class S	Class I	Class T
Shareholder Fees Column [Text]	Class A	Class C	Class S	Class I	Class T
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	5.75%	none	none	none	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	none	1.00%	none	none	none

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses INTECH U.S. Growth Fund Class A, C, S, I, T Shares	Class A	Class C	Class S	Class I	Class T
Operating Expenses Column [Text]	Class A	Class C	Class S	Class I	Class T
Management Fees	0.50%	0.50%	0.50%	0.50%	0.50%
Distribution/Service (12b-1) Fees	0.25%	1.00%	0.25%	none	none
Other Expenses	0.17%	0.21%	0.32%	0.12%	0.33%
Total Annual Fund Operating Expenses	0.92%	1.71%	1.07%	0.62%	0.83%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

If Shares are redeemed:

Expense Example INTECH U.S. Growth Fund Class A, C, S, I, T Shares (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	663	851	1,055	1,641
Class C	Class C Shares	274	539	928	2,019
Class S	Class S Shares	109	340	590	1,306
Class I	Class I Shares	63	199	346	774
Class T	Class T Shares	85	265	460	1,025

If Shares are not redeemed:

Expense Example, No Redemption INTECH U.S. Growth Fund Class A, C, S, I, T Shares (USD $)	Expense Example, No Redemption, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	663	851	1,055	1,641
Class C	Class C Shares	174	539	928	2,019
Class S	Class S Shares	109	340	590	1,306
Class I	Class I Shares	63	199	346	774
Class T	Class T Shares	85	265	460	1,025

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 84% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund invests, under normal circumstances, at least 80% of its net assets in U.S. common stocks from the universe of the Russell 1000^® Growth Index, utilizing INTECH's mathematical investment process. The Russell 1000^® Growth Index is an unmanaged index that measures the performance of those Russell 1000 companies with higher price-to-book ratios and higher forecasted growth values.

The Fund pursues its investment objective by applying a mathematical investment process to construct an investment portfolio from the universe of common stocks within its named benchmark index. The goal of this process is to build a portfolio of stocks in a more efficient combination than the named benchmark index. The process seeks to capitalize on the natural volatility of the market by searching for stocks within the index that have high relative volatility (providing the potential for excess returns) but that essentially move in opposite directions or have low correlation to each other (providing the potential for lower relative risk). By constructing the portfolio in this manner and periodically rebalancing the portfolio to maintain potentially more efficient weightings, INTECH's mathematical investment process seeks to create a portfolio that, over time, produces returns in excess of its named benchmark index with risks similar to that of the benchmark index. The rebalancing techniques used by INTECH may result in a higher portfolio turnover compared to a "buy and hold" fund strategy.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund's returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Growth Securities Risk. Securities of companies perceived to be "growth" companies may be more volatile than other stocks and may involve special risks. If a company's growth potential is not realized, the securities purchased may not perform as expected, reducing the Fund's returns. In addition, because different types of stocks tend to shift in and out of favor depending on market and economic conditions, "growth" stocks may perform differently from the market as a whole and other types of securities.

Market Risk. The value of the Fund's portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases. Further, regardless of how well individual companies or securities perform, the value of the Fund's portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Investment Process Risk. The proprietary mathematical investment process used by INTECH may not achieve the desired results. On an occasional basis, INTECH considers changes to its mathematical investment process. These changes may result in changes to the portfolio, might not provide the intended results, and may adversely impact the Fund's performance.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund's performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund's performance has varied over time. Class S Shares, Class A Shares, Class C Shares, and Class I Shares of the Fund commenced operations on July 6, 2009, after the reorganization of each corresponding class of shares of Janus Adviser INTECH Risk-Managed Growth Fund ("JAD predecessor fund") into each respective share class of the Fund. Class T Shares of the Fund commenced operations on July 6, 2009.

• The performance shown for Class S Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund's Class S Shares prior to the reorganization, calculated using the fees and expenses of the JAD predecessor fund's Class S Shares, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class A Shares reflects the performance of the JAD predecessor fund's Class A Shares from September 30, 2004 to July 6, 2009 (prior to the reorganization), calculated using the fees and expenses of Class A Shares of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers. Performance shown for certain periods prior to September 30, 2004 reflects the historical performance of the JAD predecessor fund's Class S Shares (formerly named Class I Shares), calculated using the fees and expenses of Class S Shares of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class C Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund's Class C Shares prior to the reorganization, calculated using the fees and expenses of the JAD predecessor fund's Class C Shares, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class I Shares reflects the performance of the JAD predecessor fund's Class I Shares from November 28, 2005 to July 6, 2009 (prior to the reorganization), calculated using the fees and expenses of Class I Shares of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers. Performance shown for certain periods prior to November 28, 2005 reflects the historical performance of the JAD predecessor fund's Class S Shares (formerly named Class I Shares), calculated using the fees and expenses of Class S Shares of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class T Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund's Class S Shares prior to the reorganization, calculated using the fees and expenses of Class S Shares, net of any applicable fee and expense limitations or waivers.

If Class A Shares, Class I Shares, and Class T Shares of the Fund had been available during periods prior to July 6, 2009, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund's commencement of Class S Shares, Class A Shares, Class C Shares, Class I Shares, and Class T Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Annual Total Returns for Class S Shares (calendar year-end)

Best Quarter:  Second Quarter 2009  15.04%          Worst Quarter:  Fourth Quarter 2008   −25.11%

The Fund's year-to-date return as of the calendar quarter ended September 30, 2012 was 16.23%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns INTECH U.S. Growth Fund Class A, C, S, I, T Shares	Column	Label		1 Year	5 Years	Since Inception of Predecessor Fund	Inception Date
Class S Shares Return Before Taxes	Class S Shares	Return Before Taxes		1.73%	0.07%	5.44%	Jan. 02, 2003
Class S Shares Return After Taxes on Distributions	Class S Shares	Return After Taxes on Distributions		1.66%	(0.16%)	4.92%	Jan. 02, 2003
Class S Shares Return After Taxes on Distributions and Sale of Fund Shares	Class S Shares	Return After Taxes on Distributions and Sale of Fund Shares	[1]	1.22%	0.04%	4.57%	Jan. 02, 2003
Class A Shares Return Before Taxes	Class A Shares	Return Before Taxes	[2]	(3.80%)	(0.91%)	4.96%	Jan. 02, 2003
Class C Shares Return Before Taxes	Class C Shares	Return Before Taxes	[3]	0.27%	(0.56%)	4.84%	Jan. 02, 2003
Class I Shares Return Before Taxes	Class I Shares	Return Before Taxes		2.23%	0.53%	5.44%	Jan. 02, 2003
Class T Shares Return Before Taxes	Class T Shares	Return Before Taxes		2.03%	0.07%	5.44%	Jan. 02, 2003
Russell 1000 Growth Index (reflects no deduction for expenses, fees, or taxes)		Russell 1000® Growth Index		2.64%	2.50%	6.30%	Jan. 02, 2003

After-tax returns are calculated using distributions for the Fund's Class S Shares for periods following July 6, 2009; and for the JAD predecessor fund's Class S Shares (formerly named Class I Shares) for periods prior to July 6, 2009. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class S Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class S Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

INTECH U.S. Value Fund | Class A, C, S, I, T Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

INTECH U.S. Value Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

INTECH U.S. Value Fund seeks long-term growth of capital.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

SHAREHOLDER FEES
(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

November 1, 2013

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 100% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

100.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 46 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

If Shares are redeemed:

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

If Shares are not redeemed:

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund invests, under normal circumstances, at least 80% of its net assets in U.S. common stocks from the universe of the Russell 1000^® Value Index, utilizing INTECH’s mathematical investment process. The Russell 1000^® Value Index is an unmanaged index that measures the performance of those Russell 1000 companies with lower price-to-book ratios and lower forecasted growth values.

The Fund pursues its investment objective by applying a mathematical investment process to construct an investment portfolio from the universe of common stocks within its named benchmark index. The goal of this process is to build a portfolio of stocks in a more efficient combination than the named benchmark index. The process seeks to capitalize on the natural volatility of the market by searching for stocks within the index that have high relative volatility (providing the potential for excess returns) but that essentially move in opposite directions or have low correlation to each other (providing the potential for lower relative risk). By constructing the portfolio in this manner and periodically rebalancing the portfolio to maintain potentially more efficient weightings, INTECH’s mathematical investment process seeks to create a portfolio that, over time, produces returns in excess of its named benchmark index with risks similar to that of the benchmark index. The rebalancing techniques used by INTECH may result in a higher portfolio turnover compared to a “buy and hold” fund strategy.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Investment Process Risk. The proprietary mathematical investment process used by INTECH may not achieve the desired results. On an occasional basis, INTECH considers changes to its mathematical investment process. These changes may result in changes to the portfolio, might not provide the intended results, and may adversely impact the Fund’s performance.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

The biggest risk is that the Fund’s returns will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class I Shares, Class A Shares, Class C Shares, and Class S Shares of the Fund commenced operations on July 6, 2009, after the reorganization of each corresponding class of shares of Janus Adviser INTECH Risk-Managed Value Fund (“JAD predecessor fund”) into each respective share class of the Fund. Class T Shares of the Fund commenced operations on July 6, 2009.

• The performance shown for Class I Shares, Class A Shares, Class C Shares, and Class S Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund’s Class I Shares, Class A Shares, Class C Shares, and Class S Shares prior to the reorganization, calculated using the fees and expenses of each respective share class of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class T Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund’s Class I Shares prior to the reorganization, calculated using the fees and expenses of Class T Shares, without the effect of any fee and expense limitations or waivers.

If Class T Shares of the Fund had been available during periods prior to July 6, 2009, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class I Shares, Class A Shares, Class C Shares, Class S Shares, and Class T Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-877-335-2687

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/advisor/mutual-funds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class I Shares (calendar year-end)

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Third Quarter 2009  17.79%     Worst Quarter:  Fourth Quarter 2008  −21.39%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 13.89%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

After-tax returns are calculated using distributions for the Fund’s Class I Shares for periods following July 6, 2009; and for the JAD predecessor fund’s Class I Shares for periods prior to July 6, 2009. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

INTECH U.S. Value Fund | Class A, C, S, I, T Shares | Class A

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class A

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class A

Management Fees

rr_ManagementFeesOverAssets

0.50%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.17%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.92%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

none

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.92%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleYear01

663

3 Years

rr_ExpenseExampleYear03

851

5 Years

rr_ExpenseExampleYear05

1,055

10 Years

rr_ExpenseExampleYear10

1,641

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

663

3 Years

rr_ExpenseExampleNoRedemptionYear03

851

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,055

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,641

INTECH U.S. Value Fund | Class A, C, S, I, T Shares | Class C

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class C

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

1.00%

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class C

Management Fees

rr_ManagementFeesOverAssets

0.50%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

0.36%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.86%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.11%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.75%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleYear01

289

3 Years

rr_ExpenseExampleYear03

585

5 Years

rr_ExpenseExampleYear05

1,006

10 Years

rr_ExpenseExampleYear10

2,180

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

189

3 Years

rr_ExpenseExampleNoRedemptionYear03

585

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,006

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,180

INTECH U.S. Value Fund | Class A, C, S, I, T Shares | Class S

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class S

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class S

Management Fees

rr_ManagementFeesOverAssets

0.50%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.40%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.15%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

none

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.15%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleYear01

117

3 Years

rr_ExpenseExampleYear03

365

5 Years

rr_ExpenseExampleYear05

633

10 Years

rr_ExpenseExampleYear10

1,398

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

117

3 Years

rr_ExpenseExampleNoRedemptionYear03

365

5 Years

rr_ExpenseExampleNoRedemptionYear05

633

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,398

INTECH U.S. Value Fund | Class A, C, S, I, T Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class I

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class I

Management Fees

rr_ManagementFeesOverAssets

0.50%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.17%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.67%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

none

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.67%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleYear01

68

3 Years

rr_ExpenseExampleYear03

214

5 Years

rr_ExpenseExampleYear05

373

10 Years

rr_ExpenseExampleYear10

835

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

68

3 Years

rr_ExpenseExampleNoRedemptionYear03

214

5 Years

rr_ExpenseExampleNoRedemptionYear05

373

10 Years

rr_ExpenseExampleNoRedemptionYear10

835

2006

rr_AnnualReturn2006

17.72%

2007

rr_AnnualReturn2007

1.47%

2008

rr_AnnualReturn2008

(34.79%)

2009

rr_AnnualReturn2009

17.99%

2010

rr_AnnualReturn2010

15.41%

2011

rr_AnnualReturn2011

2.28%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

13.89%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:  

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Sep. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

17.79%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:  

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(21.39%)

INTECH U.S. Value Fund | Class A, C, S, I, T Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class T

Management Fees

rr_ManagementFeesOverAssets

0.50%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.39%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.89%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

none

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.89%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleYear01

91

3 Years

rr_ExpenseExampleYear03

284

5 Years

rr_ExpenseExampleYear05

493

10 Years

rr_ExpenseExampleYear10

1,096

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

91

3 Years

rr_ExpenseExampleNoRedemptionYear03

284

5 Years

rr_ExpenseExampleNoRedemptionYear05

493

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,096

INTECH U.S. Value Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class A

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class A Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[2]

1 Year

rr_AverageAnnualReturnYear01

(3.79%)

5 Years

rr_AverageAnnualReturnYear05

(3.00%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

0.14%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

INTECH U.S. Value Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class C

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class C Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[3]

1 Year

rr_AverageAnnualReturnYear01

0.16%

5 Years

rr_AverageAnnualReturnYear05

(2.58%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

0.37%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

INTECH U.S. Value Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class S

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class S Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

1.81%

5 Years

rr_AverageAnnualReturnYear05

(2.09%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

0.89%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

INTECH U.S. Value Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

2.28%

5 Years

rr_AverageAnnualReturnYear05

(1.62%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

1.37%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

INTECH U.S. Value Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

2.07%

5 Years

rr_AverageAnnualReturnYear05

(1.98%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

0.96%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

INTECH U.S. Value Fund | Class A, C, S, I, T Shares | Return After Taxes on Distributions | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

2.02%

5 Years

rr_AverageAnnualReturnYear05

(2.01%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

0.96%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

INTECH U.S. Value Fund | Class A, C, S, I, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[4]

1 Year

rr_AverageAnnualReturnYear01

1.83%

5 Years

rr_AverageAnnualReturnYear05

(1.46%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

1.07%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

INTECH U.S. Value Fund | Class A, C, S, I, T Shares | Russell 1000 Value Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Russell 1000® Value Index

1 Year

rr_AverageAnnualReturnYear01

0.39%

5 Years

rr_AverageAnnualReturnYear05

(2.64%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

1.13%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2005

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, and Class S Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 0.75% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

[4] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Janus Global Bond Fund | Class D Shares

Fund summary

Janus Global Bond Fund

INVESTMENT OBJECTIVE

Janus Global Bond Fund seeks total return, consistent with preservation of capital.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses

Janus Global Bond Fund

Class D Shares

Class D

Operating Expenses Column [Text]

Class D

Management Fees

0.60%

Other Expenses

0.71%

Total Annual Fund Operating Expenses

^[1]

1.31%

Fee Waiver

^[1]

0.40%

Total Annual Fund Operating Expenses After Fee Waiver

^[1]

0.91%

EXAMPLE:

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers or recoupments (if applicable) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)

Expense Example, By Year, Column [Text]

1 Year

3 Years

5 Years

10 Years

Janus Global Bond Fund Class D Shares Class D

Class D Shares

133

415

718

1,579

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 222% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objective by investing, under normal circumstances, at least 80% of its net assets in bonds. Bonds include, but are not limited to, corporate bonds, government notes and bonds, convertible bonds, mortgage-backed securities, and zero-coupon bonds. The Fund invests in corporate debt securities of issuers in a number of different countries, which may include the United States. The Fund invests in securities of issuers located in developed and emerging market countries. The Fund may invest across all fixed-income sectors, including U.S. and non-U.S. government securities. The Fund’s investments may be denominated in local currency or U.S. dollar-denominated. The Fund may invest in debt securities with a range of maturities from short- to long-term. The Fund may invest up to 35% of its net assets in high-yield/high-risk debt securities. The Fund may also invest in preferred and common stock, money market instruments, municipal bonds, commercial and residential mortgage-backed securities, asset-backed securities, other securitized and structured debt products, private placements, and other investment companies, including exchange-traded funds (“ETFs”). The Fund may also invest in bank loans, euro-denominated obligations, buy backs or dollar rolls, when-issued securities, and reverse repurchase agreements. Due to the nature of securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

In addition, the Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices, as substitutes for securities in which the Fund invests. The Fund has invested in and is expected to continue to invest in collateralized forward foreign currency exchange contracts, futures, options, and swaps (including interest rate swaps, total return swaps, and credit default swaps) for hedging purposes (to offset risks associated with an investment, currency exposure, or market conditions) and to increase or decrease the Fund’s exposure to a particular market, to manage or adjust the risk profile of the Fund related to an investment or currency exposure, to adjust its currency exposure relative to its benchmark index, and to earn income and enhance returns. In particular, the Fund may use interest rate futures to manage portfolio risk. The Fund’s exposure to derivatives will vary, is not limited to those derivatives listed, and could be significant at times. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

In addition to considering economic factors such as the effect of interest rates on the Fund’s investments, the portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income-producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

PRINCIPAL INVESTMENT RISKS

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

Foreign Exposure Risk. The Fund normally has significant exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries. To the extent the Fund invests in foreign debt securities, such investments are sensitive to changes in interest rates. Additionally, investments in securities of foreign governments involve the risk that a foreign government may not be willing or able to pay interest or repay principal when due.

Eurozone Exposure Risk. The Fund’s investment may include certain securities that are denominated and traded in, or based on, the euro, the official currency of the Eurozone. European markets have recently experienced volatility and adverse trends due to concerns about economic downturns, rising government debt levels, and the possible default of government debt in several European countries, including Greece, Ireland, Italy, Portugal, and Spain. A default or debt restructuring by any European country would adversely impact holders of that country’s debt and worldwide sellers of credit default swaps linked to that country’s creditworthiness. These trends have adversely affected the value and exchange rate of the euro and may continue to significantly affect the economies of all European countries, which in turn may have a material adverse affect on a Fund’s investments in such countries, other countries that depend on European countries for significant amounts of trade or investment, or issuers with exposure to European debt.

Emerging Markets Risk. The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities involve a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. There is a risk in developing countries that a future economic or political crisis could lead to price controls, forced mergers of companies, expropriation or confiscatory taxation, seizure, nationalization, or creation of government monopolies, any of which may have a detrimental effect on the Fund’s investments. In addition, the Fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of the Fund’s investments. To the extent that the Fund invests a significant portion of its assets in the securities of issuers in or companies of a single country or region, it is more likely to be impacted by events or conditions affecting that country or region, which could have a negative impact on the Fund’s performance. Some of the risks of investing directly in foreign and emerging market securities may be reduced when the Fund invests indirectly in foreign securities through various other investment vehicles including derivatives, which also involve other risks. As of June 30, 2012, approximately 10.1% of the Fund’s investments were in emerging markets.

Sovereign Debt Risk. The Fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However, investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner. A sovereign debtor’s willingness or ability to satisfy its debt obligation may be affected by various factors including, but not limited to, its cash flow situation, the extent of its foreign currency reserves, the availability of foreign exchange when a payment is due, and the relative size of its debt position in relation to its economy as a whole. In the event of default, there may be limited or no legal remedies for collecting sovereign debt and there may be no bankruptcy proceedings through which the Fund may collect all or part of the sovereign debt that a governmental entity has not repaid.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

High-Yield/High-Risk Bond Risk. High-yield/high-risk bonds (also known as “junk bonds”) may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Bank Loan Risk. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. Participation interests and assignments involve credit, interest rate, and liquidity risk. In addition, the bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings.

Exchange-Traded Funds Risk. The Fund may purchase shares of exchange-traded funds (“ETFs”) to gain exposure to a particular portion of the market. ETFs are pooled investment vehicles, which may be managed or unmanaged, that generally seek to track the performance of a specific index. ETFs are traded on an exchange at market prices that may vary from the net asset value of their underlying investments. When the Fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF’s expenses. ETFs have certain inherent risks generally associated with investments in a portfolio of securities in which the ETF is invested, including the risk that the general level of stock prices may decline, thereby adversely affecting the value of each unit of the ETF. ETFs also involve the risk that an active trading market for an ETF’s shares may not develop or be maintained.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. The bar chart depicts the Fund’s performance during the period indicated. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Annual Total Returns for Class D Shares (calendar year-end)

Best Quarter:  Second Quarter 2011  2.84%          Worst Quarter:  Third Quarter 2011  0.60%

The Fund's year-to-date return as of the calendar quarter ended September 30, 2012 was 7.82%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Janus Global Bond Fund Class D Shares

Column

Label

1 Year

Since Inception

Inception Date

Class D Return Before Taxes

Class D Shares

Return Before Taxes

6.65%

6.59%

Dec. 28, 2010

Class D Return After Taxes on Distributions

Class D Shares

Return After Taxes on Distributions

5.31%

5.26%

Dec. 28, 2010

Class D Return After Taxes on Distributions and Sale of Fund Shares

Class D Shares

Return After Taxes on Distributions and Sale of Fund Shares

4.33%

4.85%

Dec. 28, 2010

Barclays Global Aggregate Bond Index (reflects no deduction for expenses, fees, or taxes)

Barclays Global Aggregate Bond Index

5.64%

7.16%

Dec. 28, 2010

Barclays Global Aggregate Corporate Bond Index (reflects no deduction for expenses, fees, or taxes)

Barclays Global Aggregate Corporate Bond Index

4.32%

6.05%

Dec. 28, 2010

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding administrative services fees payable pursuant to the Transfer Agency Agreement, brokerage commissions, interest, dividends, taxes, acquired fund fees and expenses, and extraordinary expenses) to 0.75% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees. For a period of three years subsequent to the Fund's commencement of operations (December 28, 2010) or until the Fund's assets exceed the first breakpoint in the investment advisory fee schedule, whichever occurs first, Janus Capital may recover from the Fund fees and expenses previously waived or reimbursed, which could then be considered a deferral, if the Fund's expense ratio, including recovered expenses, falls below the expense limit.

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Janus Flexible Bond Fund | Class D Shares

Fund summary

Janus Flexible Bond Fund

INVESTMENT OBJECTIVE

Janus Flexible Bond Fund seeks to obtain maximum total return, consistent with preservation of capital.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses

Janus Flexible Bond Fund

Class D Shares

Class D

Operating Expenses Column [Text]

Class D

Management Fees

0.41%

Other Expenses

0.18%

Total Annual Fund Operating Expenses

0.59%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)

Expense Example, By Year, Column [Text]

1 Year

3 Years

5 Years

10 Years

Janus Flexible Bond Fund Class D Shares Class D

Class D Shares

60

189

329

738

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 126% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objective by primarily investing, under normal circumstances, at least 80% of its net assets in bonds. Bonds include, but are not limited to, government notes and bonds, corporate bonds, convertible bonds, mortgage-backed securities, and zero-coupon bonds. The Fund will invest at least 65% of its assets in investment grade debt securities. As of June 30, 2012, the Fund’s weighted average maturity was 7.9 years. The Fund will limit its investment in high-yield/high-risk bonds, also known as “junk bonds,” to 35% or less of its net assets. The Fund generates total return from a combination of current income and capital appreciation, but income is usually the dominant portion. The Fund may also invest in asset-backed securities, money market instruments, bank loans, and foreign debt securities (which may include investments in emerging markets). Due to the nature of the securities in which the Fund invests, it may have relatively high portfolio turnover compared to other Funds.

In addition, the Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. In particular, the Fund may use interest rate futures to manage portfolio risk. The Fund’s exposure to derivatives will vary. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

In addition to considering economic factors such as the effect of interest rates on the Fund’s investments, the portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income-producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

PRINCIPAL INVESTMENT RISKS

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Sovereign Debt Risk. The Fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However, investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

High-Yield/High-Risk Bond Risk. High-yield/high-risk bonds may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Bank Loan Risk. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. Participation interests and assignments involve credit, interest rate, and liquidity risk. In addition, the bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. To the extent the Fund invests in foreign debt securities, such investments are sensitive to changes in interest rates. Additionally, investments in securities of foreign governments involve the risk that a foreign government may not be willing or able to pay interest or repay principal when due. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares, the predecessor share class. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses in effect during the periods shown, net of any applicable fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Annual Total Returns for Class D Shares (calendar year-end)

Best Quarter:  Third Quarter 2009  5.58%          Worst Quarter:  Second Quarter 2004  −2.99%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 7.19%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Janus Flexible Bond Fund Class D Shares

Column

Label

1 Year

5 Years

10 Years

Since Inception

Inception Date

Class D Return Before Taxes

Class D Shares

Return Before Taxes

6.63%

7.82%

6.48%

7.55%

Jul. 07, 1987

Class D Return After Taxes on Distributions

Class D Shares

Return After Taxes on Distributions

4.96%

5.94%

4.69%

4.93%

Jul. 07, 1987

Class D Return After Taxes on Distributions and Sale of Fund Shares

Class D Shares

Return After Taxes on Distributions and Sale of Fund Shares

4.52%

5.63%

4.51%

4.88%

Jul. 07, 1987

Barclays U.S. Aggregate Bond Index (reflects no deduction for expenses, fees, or taxes)

Barclays U.S. Aggregate Bond Index

7.84%

6.50%

5.78%

7.34%

Jul. 07, 1987

After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; and for the Fund’s Class J Shares, the predecessor share class, for the periods prior to February 16, 2010. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

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Janus Global Bond Fund | Class A, C, S, I, N, T Shares

Fund summary

Janus Global Bond Fund

INVESTMENT OBJECTIVE

Janus Global Bond Fund seeks total return, consistent with preservation of capital.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the "Purchases" section on page 51 of the Fund's Prospectus and in the "Purchases" section on page 83 of the Fund's Statement of Additional Information.

SHAREHOLDER FEES
(fees paid directly from your investment)

Shareholder Fees Janus Global Bond Fund Class A, C, S, I, N, T Shares	Class A	Class C	Class S	Class I	Class N	Class T
Shareholder Fees Column [Text]	Class A	Class C	Class S	Class I	Class N	Class T
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	4.75%	none	none	none	none	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	none	1.00%	none	none	none	none

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Janus Global Bond Fund Class A, C, S, I, N, T Shares		Class A	Class C	Class S	Class I	Class N		Class T
Operating Expenses Column [Text]		Class A	Class C	Class S	Class I	Class N		Class T
Management Fees		0.60%	0.60%	0.60%	0.60%	0.60%		0.60%
Distribution/Service (12b-1) Fees		0.25%	1.00%	0.25%	none	none		none
Other Expenses		0.60%	0.61%	0.77%	0.53%	0.53%	[1]	0.78%
Total Annual Fund Operating Expenses	[2]	1.45%	2.21%	1.62%	1.13%	1.13%		1.38%
Fee Waiver	[2]	0.44%	0.45%	0.36%	0.37%	0.37%		0.37%
Total Annual Fund Operating Expenses After Fee Waiver	[2]	1.01%	1.76%	1.26%	0.76%	0.76%		1.01%

EXAMPLE:

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses without waivers or recoupments (if applicable) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

If Shares are redeemed:

Expense Example Janus Global Bond Fund Class A, C, S, I, N, T Shares (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	616	912	1,230	2,128
Class C	Class C Shares	324	691	1,185	2,544
Class S	Class S Shares	165	511	881	1,922
Class I	Class I Shares	115	359	622	1,375
Class N	Class N Shares	115	359	622	1,375
Class T	Class T Shares	140	437	755	1,657

If Shares are not redeemed:

Expense Example, No Redemption Janus Global Bond Fund Class A, C, S, I, N, T Shares (USD $)	Expense Example, No Redemption, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Class A	Class A Shares	616	912	1,230	2,128
Class C	Class C Shares	224	691	1,185	2,544
Class S	Class S Shares	165	511	881	1,922
Class I	Class I Shares	115	359	622	1,375
Class N	Class N Shares	115	359	622	1,375
Class T	Class T Shares	140	437	755	1,657

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 222% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objective by investing, under normal circumstances, at least 80% of its net assets in bonds. Bonds include, but are not limited to, corporate bonds, government notes and bonds, convertible bonds, mortgage-backed securities, and zero-coupon bonds. The Fund invests in corporate debt securities of issuers in a number of different countries, which may include the United States. The Fund invests in securities of issuers located in developed and emerging market countries. The Fund may invest across all fixed-income sectors, including U.S. and non-U.S. government securities. The Fund’s investments may be denominated in local currency or U.S. dollar-denominated. The Fund may invest in debt securities with a range of maturities from short- to long-term. The Fund may invest up to 35% of its net assets in high-yield/high-risk debt securities. The Fund may also invest in preferred and common stock, money market instruments, municipal bonds, commercial and residential mortgage-backed securities, asset-backed securities, other securitized and structured debt products, private placements, and other investment companies, including exchange-traded funds (“ETFs”). The Fund may also invest in bank loans, euro-denominated obligations, buy backs or dollar rolls, when-issued securities, and reverse repurchase agreements. Due to the nature of securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

In addition, the Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices, as substitutes for securities in which the Fund invests. The Fund has invested in and is expected to continue to invest in collateralized forward foreign currency exchange contracts, futures, options, and swaps (including interest rate swaps, total return swaps, and credit default swaps) for hedging purposes (to offset risks associated with an investment, currency exposure, or market conditions) and to increase or decrease the Fund’s exposure to a particular market, to manage or adjust the risk profile of the Fund related to an investment or currency exposure, to adjust its currency exposure relative to its benchmark index, and to earn income and enhance returns. In particular, the Fund may use interest rate futures to manage portfolio risk. The Fund’s exposure to derivatives will vary, is not limited to those derivatives listed, and could be significant at times. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

In addition to considering economic factors such as the effect of interest rates on the Fund’s investments, the portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income-producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

PRINCIPAL INVESTMENT RISKS

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

Foreign Exposure Risk. The Fund normally has significant exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries. To the extent the Fund invests in foreign debt securities, such investments are sensitive to changes in interest rates. Additionally, investments in securities of foreign governments involve the risk that a foreign government may not be willing or able to pay interest or repay principal when due.

Eurozone Exposure Risk. The Fund’s investment may include certain securities that are denominated and traded in, or based on, the euro, the official currency of the Eurozone. European markets have recently experienced volatility and adverse trends due to concerns about economic downturns, rising government debt levels, and the possible default of government debt in several European countries, including Greece, Ireland, Italy, Portugal, and Spain. A default or debt restructuring by any European country would adversely impact holders of that country’s debt and worldwide sellers of credit default swaps linked to that country’s creditworthiness. These trends have adversely affected the value and exchange rate of the euro and may continue to significantly affect the economies of all European countries, which in turn may have a material adverse affect on a Fund’s investments in such countries, other countries that depend on European countries for significant amounts of trade or investment, or issuers with exposure to European debt.

Emerging Markets Risk. The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities involve a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. There is a risk in developing countries that a future economic or political crisis could lead to price controls, forced mergers of companies, expropriation or confiscatory taxation, seizure, nationalization, or creation of government monopolies, any of which may have a detrimental effect on the Fund’s investments. In addition, the Fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of the Fund’s investments. To the extent that the Fund invests a significant portion of its assets in the securities of issuers in or companies of a single country or region, it is more likely to be impacted by events or conditions affecting that country or region, which could have a negative impact on the Fund’s performance. Some of the risks of investing directly in foreign and emerging market securities may be reduced when the Fund invests indirectly in foreign securities through various other investment vehicles including derivatives, which also involve other risks. As of June 30, 2012, approximately 10.1% of the Fund’s investments were in emerging markets.

Sovereign Debt Risk. The Fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However, investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner. A sovereign debtor’s willingness or ability to satisfy its debt obligation may be affected by various factors including, but not limited to, its cash flow situation, the extent of its foreign currency reserves, the availability of foreign exchange when a payment is due, and the relative size of its debt position in relation to its economy as a whole. In the event of default, there may be limited or no legal remedies for collecting sovereign debt and there may be no bankruptcy proceedings through which the Fund may collect all or part of the sovereign debt that a governmental entity has not repaid.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

High-Yield/High-Risk Bond Risk. High-yield/high-risk bonds (also known as “junk bonds”) may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Bank Loan Risk. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. Participation interests and assignments involve credit, interest rate, and liquidity risk. In addition, the bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings.

Exchange-Traded Funds Risk. The Fund may purchase shares of exchange-traded funds (“ETFs”) to gain exposure to a particular portion of the market. ETFs are pooled investment vehicles, which may be managed or unmanaged, that generally seek to track the performance of a specific index. ETFs are traded on an exchange at market prices that may vary from the net asset value of their underlying investments. When the Fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF’s expenses. ETFs have certain inherent risks generally associated with investments in a portfolio of securities in which the ETF is invested, including the risk that the general level of stock prices may decline, thereby adversely affecting the value of each unit of the ETF. ETFs also involve the risk that an active trading market for an ETF’s shares may not develop or be maintained.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund's performance has varied over time. Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class T Shares of the Fund commenced operations with the Fund's inception.

• The performance shown for Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class T Shares is calculated using the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class N Shares reflects the performance of the Fund's Class I Shares, calculated using the fees and expenses of Class N Shares, without the effect of any fee and expense limitations or waivers. If Class N Shares of the Fund had been available during the periods shown, the performance may have been different.

The bar chart depicts the Fund's performance during the period indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund's average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund's performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Annual Total Returns for Class I Shares (calendar year-end)

Best Quarter:  Second Quarter 2011  2.77%          Worst Quarter:  Third Quarter 2011  0.72%

The Fund's year-to-date return as of the calendar quarter ended September 30, 2012 was 7.94%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Janus Global Bond Fund Class A, C, S, I, N, T Shares	Column	Label		1 Year	Since Inception	Inception Date
Class I Shares Return Before Taxes	Class I Shares	Return Before Taxes		6.67%	6.62%	Dec. 28, 2010
Class I Shares Return After Taxes on Distributions	Class I Shares	Return After Taxes on Distributions		5.29%	5.24%	Dec. 28, 2010
Class I Shares Return After Taxes on Distributions and Sale of Fund Shares	Class I Shares	Return After Taxes on Distributions and Sale of Fund Shares		4.34%	4.84%	Dec. 28, 2010
Class A Shares Return Before Taxes	Class A Shares	Return Before Taxes	[1]	1.44%	1.42%	Dec. 28, 2010
Class C Shares Return Before Taxes	Class C Shares	Return Before Taxes	[2]	4.78%	5.76%	Dec. 28, 2010
Class S Shares Return Before Taxes	Class S Shares	Return Before Taxes		6.34%	6.29%	Dec. 28, 2010
Class N Shares Return Before Taxes	Class N Shares	Return Before Taxes		6.27%	6.21%	Dec. 28, 2010
Class T Shares Return Before Taxes	Class T Shares	Return Before Taxes		6.51%	6.45%	Dec. 28, 2010
Barclays Global Aggregate Bond Index (reflects no deduction for expenses, fees, or taxes)		Barclays Global Aggregate Bond Index		5.64%	7.16%	Dec. 28, 2010
Barclays Global Aggregate Corporate Bond Index (reflects no deduction for expenses, fees, or taxes)		Barclays Global Aggregate Corporate Bond Index		4.32%	6.05%	Dec. 28, 2010

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

[1] Other Expenses for Class N Shares are based on the estimated expenses that the Shares expect to incur during their initial fiscal period.

[2] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, and Class S Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 0.75% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees. For a period of three years subsequent to the Fund's commencement of operations (December 28, 2010) or until the Fund's assets exceed the first breakpoint in the investment advisory fee schedule, whichever occurs first, Janus Capital may recover from the Fund fees and expenses previously waived or reimbursed, which could then be considered a deferral, if the Fund's expense ratio, including recovered expenses, falls below the expense limit.

[1] Calculated assuming maximum permitted sales loads.

[2] The one year return is calculated to include the contingent deferred sales charge.

XML

Label

Element

Value

Risk/Return:

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Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

INTECH U.S. Core Fund | Class D Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

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Fund summary

INTECH U.S. Core Fund

Objective [Heading]

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INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

INTECH U.S. Core Fund seeks long-term growth of capital.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 73% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

73.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund invests, under normal circumstances, at least 80% of its net assets in U.S. common stocks from the universe of the S&P 500^® Index, utilizing INTECH’s mathematical investment process. The S&P 500^® Index is an unmanaged index of 500 stocks that is generally representative of the performance of larger companies in the United States.

The Fund pursues its investment objective by applying a mathematical investment process to construct an investment portfolio from the universe of common stocks within its named benchmark index. The goal of this process is to build a portfolio of stocks in a more efficient combination than the named benchmark index. The process seeks to capitalize on the natural volatility of the market by searching for stocks within the index that have high relative volatility (providing the potential for excess returns) but that essentially move in opposite directions or have low correlation to each other (providing the potential for lower relative risk). By constructing the portfolio in this manner and periodically rebalancing the portfolio to maintain potentially more efficient weightings, INTECH’s mathematical investment process seeks to create a portfolio that, over time, produces returns in excess of its named benchmark index with risks similar to that of the benchmark index. The rebalancing techniques used by INTECH may result in a higher portfolio turnover compared to a “buy and hold” fund strategy.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Investment Process Risk. The proprietary mathematical investment process used by INTECH may not achieve the desired results. On an occasional basis, INTECH considers changes to its mathematical investment process. These changes may result in changes to the portfolio, might not provide the intended results, and may adversely impact the Fund’s performance.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

The biggest risk is that the Fund’s returns will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

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PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares, the predecessor share class. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses in effect during the periods shown, net of any applicable fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-800-525-3713

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/allfunds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

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Annual Total Returns for Class D Shares (calendar year-end)

Bar Chart Closing [Text Block]

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Best Quarter:  Second Quarter 2009  14.79%        Worst Quarter:  Fourth Quarter 2008 -21.49%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 14.92%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; and for the Fund’s Class J Shares, the predecessor share class, for the periods prior to February 16, 2010. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

INTECH U.S. Core Fund | Class D Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class D

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.54%

Other Expenses

rr_OtherExpensesOverAssets

0.30%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.84%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class D Shares

1 Year

rr_ExpenseExampleYear01

86

3 Years

rr_ExpenseExampleYear03

268

5 Years

rr_ExpenseExampleYear05

466

10 Years

rr_ExpenseExampleYear10

1,037

2004

rr_AnnualReturn2004

17.68%

2005

rr_AnnualReturn2005

11.06%

2006

rr_AnnualReturn2006

11.37%

2007

rr_AnnualReturn2007

6.40%

2008

rr_AnnualReturn2008

(36.57%)

2009

rr_AnnualReturn2009

22.91%

2010

rr_AnnualReturn2010

16.38%

2011

rr_AnnualReturn2011

5.07%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

14.92%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Sep. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

14.79%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(21.49%)

INTECH U.S. Core Fund | Class D Shares | Return Before Taxes | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

5.07%

5 Years

rr_AverageAnnualReturnYear05

0.29%

Since Inception

rr_AverageAnnualReturnSinceInception

7.81%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 28, 2003

INTECH U.S. Core Fund | Class D Shares | Return After Taxes on Distributions | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

4.92%

5 Years

rr_AverageAnnualReturnYear05

(0.20%)

Since Inception

rr_AverageAnnualReturnSinceInception

7.08%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 28, 2003

INTECH U.S. Core Fund | Class D Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[1]

1 Year

rr_AverageAnnualReturnYear01

3.50%

5 Years

rr_AverageAnnualReturnYear05

0.21%

Since Inception

rr_AverageAnnualReturnSinceInception

6.74%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 28, 2003

INTECH U.S. Core Fund | Class D Shares | S&P 500 Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

S&P 500® Index

1 Year

rr_AverageAnnualReturnYear01

2.11%

5 Years

rr_AverageAnnualReturnYear05

(0.25%)

Since Inception

rr_AverageAnnualReturnSinceInception

6.77%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 28, 2003

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Perkins Mid Cap Value Fund | Class L Shares

Fund summary

Perkins Mid Cap Value Fund

INVESTMENT OBJECTIVE

Perkins Mid Cap Value Fund seeks capital appreciation.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses	Perkins Mid Cap Value Fund Class L Shares Class L
Operating Expenses Column [Text]	Class L
Management Fees (may adjust up or down)	0.54%
Other Expenses	0.30%
Total Annual Fund Operating Expenses	0.84%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Perkins Mid Cap Value Fund Class L Shares Class L	Class L Shares	86	268	466	1,037

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 54% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objective by investing primarily in common stocks selected for their capital appreciation potential. The Fund primarily invests in the common stocks of mid-sized companies whose stock prices the portfolio managers believe to be undervalued. The Fund invests, under normal circumstances, at least 80% of its net assets in equity securities of companies whose market capitalization falls, at the time of purchase, within the 12-month average of the capitalization range of the Russell Midcap® Value Index. This average is updated monthly. The market capitalizations within the index will vary, but as of June 30, 2012, they ranged from approximately $1.3 billion to $18.5 billion. The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets. The Fund may invest, under normal circumstances, up to 20% of its net assets in securities of companies having market capitalizations outside of the aforementioned market capitalization ranges. In addition, when the portfolio managers believe that market conditions are unfavorable for investing, or when they are otherwise unable to locate attractive investment opportunities, the Fund may invest up to 20% of its net assets in cash or similar investments.

The Fund focuses on companies that have fallen out of favor with the market or that appear to be temporarily misunderstood by the investment community. The Fund’s portfolio managers generally look for companies with:

• strong balance sheets and solid recurring free cash flows
• attractive relative and absolute valuation ratios or that have underperformed recently
• favorable reward to risk characteristics

The Fund may also invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. The Fund has and is expected to continue to buy and sell put and call options, particularly on market indices, for hedging purposes (to offset risks associated with an investment, currency exposure, or market conditions) and to enhance returns. The Fund’s exposure to derivatives will vary, is not limited to those derivatives listed, and could be significant at times. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s portfolio managers. When the Fund’s investments in cash or similar investments increase due to a lack of favorable investment opportunities or other extraordinary factors, the Fund may not participate in market advances or declines to the same extent that it would if the Fund had been fully invested.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Mid-Sized Companies Risk. The Fund’s investments in securities issued by mid-sized companies may involve greater risks than are customarily associated with larger, more established companies. Securities issued by mid-sized companies tend to be more volatile than securities issued by larger or more established companies and may underperform as compared to the securities of larger companies.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. The performance shown for periods following April 21, 2003, reflects the fees and expenses of Class L Shares (formerly named Institutional Shares), net of any applicable fee and expense limitations or waivers. The performance shown for Class L Shares for the periods from May 17, 2002 to April 17, 2003, reflects the historical performance of Berger Mid Cap Value Fund – Institutional Shares (as a result of a prior reorganization of Berger Mid Cap Value Fund – Institutional Shares into the Fund’s Class L Shares). For the periods prior to May 17, 2002, the performance shown reflects the historical performance of Berger Mid Cap Value Fund – Investor Shares.

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Annual Total Returns for Class L Shares (calendar year-end)

^[1]

Best Quarter:  Second Quarter 2003  17.19%          Worst Quarter:  Fourth Quarter 2008  −19.56%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 9.05%.

Average Annual Total Returns Perkins Mid Cap Value Fund		Caption	Column	Label		1 Year	5 Years	10 Years	Since Inception of Predecessor Fund	Inception Date
Class L Shares	[1]	Average Annual Total Returns (periods ended 12/31/11)
Class L Shares Return Before Taxes Class L			Class L Shares	Return Before Taxes		(2.33%)	2.84%	7.79%	11.92%	Aug. 12, 1998
Class L Shares Return After Taxes on Distributions Class L			Class L Shares	Return After Taxes on Distributions		(3.70%)	1.81%	6.66%	10.45%	Aug. 12, 1998
Class L Shares Return After Taxes on Distributions and Sale of Fund Shares Class L			Class L Shares	Return After Taxes on Distributions and Sale of Fund Shares	[2]	(0.03%)	2.21%	6.51%	10.08%	Aug. 12, 1998
Class L Shares Russell Midcap Value Index (reflects no deduction for expenses, fees, or taxes)				Russell Midcap® Value Index		(1.38%)	0.04%	7.67%	7.70%	Aug. 12, 1998

After-tax returns are calculated using distributions for the Fund’s Class L Shares (formerly named Institutional Shares) for the periods following April 21, 2003 for Berger Mid Cap Value Fund – Institutional Shares for the period May 17, 2002 to April 17, 2003; and for Berger Mid Cap Value Fund – Investor Shares for periods prior to May 17, 2002. If Class L Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

[1] Fund returns for periods prior to the Fund's adoption of share classes reflect a 0.25% 12b-1 fee, which has not been paid by the Class L Shares (formerly named Institutional Shares) since the class commenced investment operations on May 17, 2002.

[2] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

[1] Fund returns for periods prior to the Fund's adoption of share classes reflect a 0.25% 12b-1 fee, which has not been paid by the Class L Shares (formerly named Institutional Shares) since the class commenced investment operations on May 17, 2002.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	JANUS INVESTMENT FUND
Prospectus Date	rr_ProspectusDate	Oct. 26, 2012
Perkins Select Value Fund | Class D Shares
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Fund summary Perkins Select Value Fund
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Perkins Select Value Fund seeks capital appreciation.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE FUND
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	November 1, 2013
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover:
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the period December 15, 2011 to June 30, 2012, the Fund’s portfolio turnover rate was 80% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	80.00%
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE:
Expense Example by Year [Heading]	rr_ExpenseExampleByYearHeading	The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Fund pursues its investment objective by investing primarily in common stocks selected for their capital appreciation potential. The Fund primarily invests in the common stocks of companies of any size whose stock prices the portfolio managers believe to be undervalued. The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets. In addition, when the portfolio managers believe that market conditions are unfavorable for investing, or when they are otherwise unable to locate attractive investment opportunities, the Fund’s cash or similar investments may increase. The Fund focuses on companies that have fallen out of favor with the market or that appear to be temporarily misunderstood by the investment community. The Fund’s portfolio managers generally look for companies with: strong balance sheets and solid recurring free cash flows attractive relative and absolute valuation ratios or that have underperformed recently favorable reward to risk characteristics The Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices, as substitutes for securities in which the Fund invests. The Fund may invest in derivative instruments (by taking long and/or short positions) for different purposes, including hedging (to offset risks associated with an investment, currency exposure, or market conditions) and to earn income and enhance returns. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.
Risk [Heading]	rr_RiskHeading	PRINCIPAL INVESTMENT RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices. Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s portfolio managers. When the Fund’s investments in cash or similar investments increase due to a lack of favorable investment opportunities or other extraordinary factors, the Fund may not participate in market advances or declines to the same extent that it would if the Fund had been fully invested. Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money. Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries. Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets. Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Risk Lose Money [Text]	rr_RiskLoseMoney	The biggest risk is that the Fund’s returns will vary, and you could lose money.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	PERFORMANCE INFORMATION
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The Fund does not have a full calendar year of operations. Performance information for certain periods is included in the Fund’s first annual and/or semiannual report.
Performance One Year or Less [Text]	rr_PerformanceOneYearOrLess	The Fund does not have a full calendar year of operations.
Perkins Select Value Fund | Class D Shares | Class D
Risk/Return:	rr_RiskReturnAbstract
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class D
Management Fees (may adjust up or down)	rr_ManagementFeesOverAssets	0.70%
Other Expenses	rr_OtherExpensesOverAssets	1.04%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.74%	[1]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	0.55%	[1]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.19%	[1]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class D Shares
1 Year	rr_ExpenseExampleYear01	177
3 Years	rr_ExpenseExampleYear03	548
5 Years	rr_ExpenseExampleYear05	944
10 Years	rr_ExpenseExampleYear10	2,052

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding any performance adjustments to management fees, administrative services fees payable pursuant to the Transfer Agency Agreement, brokerage commissions, interest, dividends, taxes, acquired fund fees and expenses, and extraordinary expenses) to 1.00% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

XML

Janus Short-Term Bond Fund | Class D Shares

Fund summary

Janus Short-Term Bond Fund

INVESTMENT OBJECTIVE

Janus Short-Term Bond Fund seeks as high a level of current income as is consistent with preservation of capital.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses		Janus Short-Term Bond Fund Class D Shares Class D
Operating Expenses Column [Text]		Class D
Management Fees		0.55%
Other Expenses		0.19%
Total Annual Fund Operating Expenses	[1]	0.74%
Fee Waiver	[1]	0.05%
Total Annual Fund Operating Expenses After Fee Waiver	[1]	0.69%

EXAMPLE:

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Janus Short-Term Bond Fund Class D Shares Class D	Class D Shares	76	237	411	918

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 93% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund invests, under normal circumstances, at least 80% of its net assets in short- and intermediate-term securities such as corporate bonds or notes or government securities, including agency securities. The Fund may invest up to 35% of its net assets in high-yield/high risk bonds, also known as “junk bonds.” The Fund expects to maintain an average-weighted effective maturity of three years or less under normal circumstances. As of June 30, 2012, the Fund’s weighted average maturity was 2.4 years. The Fund may also invest in bank loans, mortgage-backed securities, asset-backed securities, and foreign debt securities (which may include investments in emerging markets). Due to the nature of securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

“Effective” maturity differs from actual maturity, which may be longer. In calculating the “effective” maturity the portfolio managers will estimate the effect of expected principal payments and call provisions on securities held in the portfolio. This gives the portfolio managers some additional flexibility in the securities they purchase, but all else being equal, could result in more volatility than if the Fund calculated an actual maturity target.

In addition, the Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. In particular, the Fund may use interest rate futures to manage portfolio risk. The Fund’s exposure to derivatives will vary. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

In addition to considering economic factors such as the effect of interest rates on the Fund’s investments, the portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income-producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

PRINCIPAL INVESTMENT RISKS

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

Sovereign Debt Risk. The Fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However, investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Bank Loan Risk. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. Participation interests and assignments involve credit, interest rate, and liquidity risk. In addition, the bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. To the extent the Fund invests in foreign debt securities, such investments are sensitive to changes in interest rates. Additionally, investments in securities of foreign governments involve the risk that a foreign government may not be willing or able to pay interest or repay principal when due. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

High-Yield/High-Risk Bond Risk. High-yield/high-risk bonds may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares, the predecessor share class. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses in effect during the periods shown, net of any applicable fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Annual Total Returns for Class D Shares (calendar year-end)

Best Quarter:  Second Quarter 2009  3.18%          Worst Quarter:  Second Quarter 2008  −0.90%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 3.05%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Janus Short-Term Bond Fund Class D Shares	Column	Label		1 Year	5 Years	10 Years	Since Inception	Inception Date
Class D Return Before Taxes	Class D Shares	Return Before Taxes		1.50%	4.65%	3.83%	4.65%	Sep. 01, 1992
Class D Return After Taxes on Distributions	Class D Shares	Return After Taxes on Distributions		0.66%	3.43%	2.63%	2.93%	Sep. 01, 1992
Class D Return After Taxes on Distributions and Sale of Fund Shares	Class D Shares	Return After Taxes on Distributions and Sale of Fund Shares	[1]	1.01%	3.27%	2.58%	2.90%	Sep. 01, 1992
Barclays 1-3 Year U.S. Government/Credit Index (reflects no deduction for expenses, fees, or taxes)		Barclays 1-3 Year U.S. Government/Credit Index		1.59%	3.99%	3.63%	4.80%	Sep. 01, 1992

After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; and for the Fund’s Class J Shares, the predecessor share class, for the periods prior to February 16, 2010. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding administrative services fees payable pursuant to the Transfer Agency Agreement, brokerage commissions, interest, dividends, taxes, acquired fund fees and expenses, and extraordinary expenses) to 0.55% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Label

Element

Value

Risk/Return:

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Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Janus Money Market Fund | Class D Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

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Fund summary

Janus Money Market Fund

Objective [Heading]

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INVESTMENT OBJECTIVES

Objective, Primary [Text Block]

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Janus Money Market Fund seeks capital preservation and liquidity

Objective, Secondary [Text Block]

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with current income as a secondary objective.

Expense [Heading]

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FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Expense Example [Heading]

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EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

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The Fund pursues its investment objectives by investing primarily in high quality debt obligations and obligations of financial institutions. Debt obligations may include commercial paper, notes and bonds, and variable amount master demand notes. Obligations of financial institutions include certificates of deposit and time deposits. The Fund also intends to invest in repurchase agreements including those secured by U.S. Government agencies. Some government agencies backed by the full faith and credit of the United States are supported by the issuer’s ability to borrow from the United States Treasury, some are supported only by the credit of the issuer, and some are supported by the United States in some other way.

The Fund will:

• invest in high quality, short-term money market instruments that present minimal credit risks, as determined by Janus Capital

• invest only in U.S. dollar-denominated instruments that have a remaining maturity of 397 days or less (as calculated pursuant to Rule 2a-7 under the Investment Company Act of 1940, as amended)

• maintain a dollar-weighted average portfolio maturity of 60 days or less and maintain a dollar-weighted average portfolio life (portfolio maturity measured without reference to any maturity shortening provisions of adjustable rate securities by reference to their interest rate reset dates) of 120 days or less

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

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Market Risk. The Fund’s yield will vary as the short-term securities in its portfolio mature and the proceeds are reinvested in securities with different interest rates. For capital preservation and liquidity, the Fund may have a greater concentration in short-term securities including, but not limited to, investing up to all of its assets in overnight securities, which may result in a reduction of the Fund’s yield. Over time, the real value of the Fund’s yield may be eroded by inflation. Although the Fund invests only in high-quality, short-term money market instruments, there is a risk that the value of the securities it holds will fall as a result of changes in interest rates, an issuer’s actual or perceived creditworthiness, or an issuer’s ability to meet its obligations. The credit quality of the Fund’s holdings can change rapidly in certain market environments and any downgrade or default of a portfolio security could cause the Fund’s share price or yield to fall.

Collateral Risk. With respect to collateral received in repurchase transactions or other investments, the Fund may have significant exposure to financial services, mortgage markets, and government agencies not secured by the full faith and credit of the United States. Such exposure, depending on market conditions, could have a negative impact on the Fund, including minimizing the value of any collateral.

Money Market Risk. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund.

Risk Money Market Fund [Text]

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Money Market Risk. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund.

Bar Chart and Performance Table [Heading]

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PERFORMANCE INFORMATION

Performance Narrative [Text Block]

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The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares, the predecessor share class. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses in effect during the periods shown, net of any applicable fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table shows how the Fund’s returns over different periods average out. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-800-525-3713

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/allfunds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

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Annual Total Returns for Class D Shares (calendar year-end)

Bar Chart Closing [Text Block]

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Best Quarter:  Fourth Quarter 2006  1.23%          Worst Quarter:  Third Quarter 2011  0.00%

Year to Date Return, Label

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The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 0.00%.

Performance Table Heading

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Average Annual Total Returns (periods ended 12/31/11)

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Money Market Seven Day Yield, Caption [Text]

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The 7-day yield on December 31, 2011 was 0.01% for Janus Money Market Fund.

Money Market Seven Day Yield

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0.01%

Janus Money Market Fund | Class D Shares | Class D

Risk/Return:

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Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class D

Management Fees

rr_ManagementFeesOverAssets

0.20%

Other Expenses

rr_OtherExpensesOverAssets

0.47%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.67%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class D Shares

1 Year

rr_ExpenseExampleYear01

68

3 Years

rr_ExpenseExampleYear03

214

5 Years

rr_ExpenseExampleYear05

373

10 Years

rr_ExpenseExampleYear10

835

2002

rr_AnnualReturn2002

1.38%

2003

rr_AnnualReturn2003

0.71%

2004

rr_AnnualReturn2004

0.93%

2005

rr_AnnualReturn2005

2.77%

2006

rr_AnnualReturn2006

4.60%

2007

rr_AnnualReturn2007

4.86%

2008

rr_AnnualReturn2008

2.09%

2009

rr_AnnualReturn2009

0.07%

2010

rr_AnnualReturn2010

0.01%

2011

rr_AnnualReturn2011

0.01%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

0.00%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Dec. 31, 2006

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

1.23%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

0.00%

Janus Money Market Fund | Class D Shares | Return Before Taxes | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

0.01%

5 Years

rr_AverageAnnualReturnYear05

1.39%

10 Years

rr_AverageAnnualReturnYear10

1.73%

Since Inception

rr_AverageAnnualReturnSinceInception

3.08%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 14, 1995

XML

Label

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Value

Risk/Return:

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Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Janus World Allocation Fund | Class A, C, S, I, T Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Janus World Allocation Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

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Janus World Allocation Fund seeks long-term growth of capital with a secondary emphasis on income.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

SHAREHOLDER FEES
(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

November 1, 2013

Portfolio Turnover [Heading]

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Portfolio Turnover:

Portfolio Turnover [Text Block]

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The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 36% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

36.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 31 of the Fund’s Prospectus and in the “Purchases” section on page 64 of the Fund’s Statement of Additional Information.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses (including the operating expenses of the underlying funds) without waivers remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

If Shares are redeemed:

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

If Shares are not redeemed:

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

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The Fund pursues its investment objective by investing in a diversified portfolio of other Janus mutual funds (“underlying funds”) and securities that provide exposure to issuers located throughout the world. Through its investment in the underlying funds, the Fund invests in issuers from several different countries, including the United States, and may, under unusual circumstances, be invested in a single country. The Fund may also have significant exposure to emerging markets. Because it invests in other funds, the Fund is considered a “fund of funds.” The Fund utilizes Janus Capital’s proprietary process to allocate assets across the following three asset categories (as defined by Janus Capital):

•   Core – The Core category seeks to provide market-like exposure by investing in funds that in turn primarily invest in a broad range of traditional asset classes such as large-, mid-, and small-cap stocks, U.S. and non-U.S. stocks, growth and value stocks, and investment-grade bonds. While not a primary strategy, the underlying funds may also invest in emerging market stocks and high-yield bonds. A primary goal of the underlying funds in the Core category is to provide shareholders with access to a broad range of investable assets in proportion to each asset class’ representation in today’s global, integrated market as determined by Janus Capital.

•   Alpha – The Alpha category seeks to generate higher-than-market returns on a risk-adjusted basis by investing in funds that in turn invest in a broad range of traditional asset classes such as large-, mid-, and small-cap stocks, U.S. and non-U.S. stocks, growth and value stocks, emerging market stocks, investment-grade bonds, and high-yield bonds. Unlike funds in the Core category, the Alpha category is less focused on the asset class composition of the global market. Instead, the Alpha category is comprised of funds, unconstrained by asset class or investment style, that Janus Capital believes may generate higher-than-market returns over a market cycle.

•   Alternative – The Alternative category is comprised of non-traditional investments with historically low correlation to the assets in the Core and Alpha categories, such as certain exchange-traded funds (“ETFs”), exchange-traded notes (“ETNs”), investments with hedge fund strategy exposure, commodities-related securities, real estate-related securities, and structured products.

The Fund attempts to maximize returns by investing the Fund’s assets in underlying funds investing in stocks (U.S. and non-U.S.), bonds, cash equivalents, alternative asset classes (such as real estate-related securities and commodity-related securities), and alternative investment strategies (such as leveraged and sector-based strategies). The target allocation of the Fund’s assets among underlying funds is based on an optimization process that utilizes quantitative analysis of a number of factors, such as historical risk, performance, fund classifications, and the relationship among underlying funds, as well as the portfolio manager’s judgment. Janus Capital analyzes Fund allocations on a regular basis in order to integrate current market data and reallocates on a quarterly basis.

The Fund’s portfolio manager determines the overall composition of the Fund, oversees the investment process, and is responsible for the day-to-day management of the Fund. The portfolio manager consults with a committee comprised of Janus Capital investment professionals (“Asset Allocation Committee”) to regularly review the process and the allocation of the Fund’s assets among the underlying funds to determine modifications to the underlying funds’ asset categories and/or weightings, or to substitute other underlying funds to emphasize and mitigate risk exposures that may arise as a result of the implementation of the allocations. The portfolio manager and Asset Allocation Committee normally review asset allocations on a quarterly basis. The portfolio manager oversees the implementation of trades on behalf of the Fund.

The Fund’s investments will be rebalanced to the identified optimal weightings on a quarterly basis, although more frequent changes can occur. The Fund’s asset class or category, category allocations, underlying funds, or underlying fund weightings may change without prior shareholder notice.

The Fund will normally allocate approximately 90% of its assets to Janus-managed mutual funds and approximately 10% to unaffiliated pooled investment vehicles (e.g., ETFs) and derivatives. For information on the potential underlying Janus funds currently available for investment by the Fund, including investment objectives and strategies, see “Investment Objectives and Strategies of the Underlying Funds” in Appendix A.

The Fund may invest in ETFs and ETNs to complement its investment in the underlying funds if there are asset classes not covered by the underlying funds or to better manage cash positions.

The Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices, as substitutes for securities in which the Fund invests. The Fund may invest in derivative instruments (by taking long and/or short positions) including, but not limited to, swap agreements to earn income and enhance uncorrelated returns, to increase or decrease exposure to a particular market, to manage or adjust the risk profile of the Fund, or as alternatives to direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

When market conditions dictate a more defensive strategy, the Fund or an underlying fund may temporarily hold cash or invest its assets in temporary investments. In that case, the Fund may take positions that are inconsistent with its investment objective. As a result, the Fund may not achieve its investment objective.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking growth of capital and, to a lesser extent, income. Investments in a portfolio with common stock and alternative investment exposure tend to be more volatile than many other investment choices.

Main Risks Associated with the Fund
Allocation Risk. The Fund’s ability to achieve its investment objective depends largely upon the portfolio manager’s allocation of assets among the underlying funds and other securities, using the optimization process and the judgment of the portfolio manager. You could lose money on your investment in the Fund as a result of these allocations. The Fund will typically invest in a number of different underlying funds; however, to the extent that the Fund invests a significant portion of its assets in a single underlying fund, it will be more sensitive to the risks associated with that fund and any investments in which that fund concentrates.

Derivatives Risk. The Fund and certain underlying funds may invest in derivatives. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

Commodity-Linked Derivative Investment Risk. The Fund may invest in derivatives that have exposure to the commodities markets. This exposure may subject the Fund to greater volatility than investments in traditional securities. The value of a commodity-linked derivative investment typically is based upon the price movements of a physical commodity (such as heating oil, livestock, or agricultural products), a commodity futures contract or commodity index, or some other readily measurable economic variable. The value of commodity-linked derivative instruments may therefore be affected by changes in overall market movements, volatility of the underlying benchmark, changes in interest rates, or other factors affecting a particular industry or commodity such as drought, floods, weather, livestock disease, embargoes, tariffs, and international economic, political, and regulatory developments.

Exchange-Traded Funds Risk. The Fund may purchase shares of ETFs to gain exposure to a particular portion of the market. ETFs are pooled investment vehicles, which may be managed or unmanaged, that generally seek to track the performance of a specific index. ETFs are traded on an exchange at market prices that may vary from the net asset value of their underlying investments. When the Fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF’s expenses. ETFs have certain inherent risks generally associated with investments in a portfolio of securities in which the ETF is invested, including the risk that the general level of stock prices may decline, thereby adversely affecting the value of each unit of the ETF. ETFs also involve the risk that an active trading market for an ETF’s shares may not develop or be maintained.

Affiliated Fund Risk. Janus Capital has the authority to select and substitute underlying affiliated mutual funds. The fees paid to Janus Capital by some Janus mutual funds are generally higher than the fees paid to Janus Capital by the Fund or by other funds and share classes available for investment by the Fund. These conditions may create a conflict of interest when selecting underlying affiliated mutual funds and share classes for investment. Janus Capital, however, is a fiduciary to the Fund and its shareholders and is legally obligated to act in their best interest when selecting underlying affiliated mutual funds.

Main Risks Associated with the Underlying Funds and Securities
The biggest risk is that the underlying funds’ returns will vary, and you could lose money.

Market Risk. Underlying funds investing in equity securities are subject to the risks associated with investments in common stocks, which tend to be more volatile than many other investment choices. The value of an underlying fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if a portfolio manager’s belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of an underlying fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Fixed-Income Securities Risk. Through the Fund’s investments in underlying funds holding fixed-income securities, the Fund is subject to the risks associated with investments in a variety of fixed-income securities, which may be less volatile than underlying funds that invest most of their assets in common stocks; returns and yields will vary, and you could lose money. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause an underlying fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which an underlying fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that an underlying fund’s portfolio manager would like or at the price that the portfolio manager believes the security is currently worth.

Foreign Exposure Risk. The Fund and certain underlying funds may have significant exposure to foreign markets as a result of their investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, the Fund’s and an underlying fund’s returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. A market swing in one or more countries or regions where the Fund or an underlying fund has invested a significant amount of its assets may have a greater effect on the Fund’s or an underlying Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s or an underlying fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Emerging Markets Risk. The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities involve a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. In addition, the Fund’s or an underlying fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of the Fund’s or an underlying fund’s investments. To the extent that the Fund or an underlying fund invests a significant portion of its assets in the securities of issuers in or companies of a single country or region, it is more likely to be impacted by events or conditions affecting that country or region, which could have a negative impact on the Fund’s performance. Some of the risks of investing directly in foreign and emerging market securities may be reduced when the Fund or an underlying fund invests indirectly in foreign securities through various other investment vehicles including derivatives, which also involve other risks.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Sovereign Debt Risk. An underlying fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

The biggest risk is that the Fund’s returns will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

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PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class I Shares, Class A Shares, Class C Shares, and Class S Shares of the Fund commenced operations on July 6, 2009, after the reorganization of each corresponding class of shares of Janus Adviser Modular Portfolio Construction^® Fund (“JAD predecessor fund”) into each respective share class of the Fund. Class T Shares of the Fund commenced operations on July 6, 2009.

• The performance shown for Class I Shares, Class A Shares, Class C Shares, and Class S Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund’s Class I Shares, Class A Shares, Class C Shares and Class S Shares prior to the reorganization, calculated using the fees and expenses of each respective share class of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class T Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund’s Class I Shares prior to the reorganization, calculated using the fees and expenses of Class T Shares, without the effect of any fee and expense limitations or waivers.

If Class T Shares of the Fund had been available during periods prior to July 6, 2009, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class I Shares, Class A Shares, Class C Shares, Class S Shares, and Class T Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. Performance information for each underlying fund is available in its prospectus and/or the most recent annual or semiannual report. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-877-335-2687

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/advisor/mutual-funds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class I Shares (calendar year-end)

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Second Quarter 2009  14.90%          Worst Quarter:  Third Quarter 2011  −13.38%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 8.19%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

The World Allocation Index is an internally-calculated, hypothetical combination of unmanaged indices that combines total returns from the MSCI All Country World Index^sm (65%) and the Barclays Global Aggregate Bond Index (35%).

After-tax returns are calculated using distributions for the Fund’s Class I Shares for periods following July 6, 2009; and for the JAD predecessor fund’s Class I Shares for periods prior to July 6, 2009. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Janus World Allocation Fund | Class A, C, S, I, T Shares | Class A

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class A

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class A

Management Fees

rr_ManagementFeesOverAssets

0.07%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

1.73%

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.74%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

2.79%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

1.33%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.46%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleYear01

841

3 Years

rr_ExpenseExampleYear03

1,390

5 Years

rr_ExpenseExampleYear05

1,964

10 Years

rr_ExpenseExampleYear10

3,514

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

841

3 Years

rr_ExpenseExampleNoRedemptionYear03

1,390

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,964

10 Years

rr_ExpenseExampleNoRedemptionYear10

3,514

Janus World Allocation Fund | Class A, C, S, I, T Shares | Class C

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class C

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

1.00%

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class C

Management Fees

rr_ManagementFeesOverAssets

0.07%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

1.84%

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.74%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

3.65%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

1.44%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

2.21%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleYear01

467

3 Years

rr_ExpenseExampleYear03

1,117

5 Years

rr_ExpenseExampleYear05

1,888

10 Years

rr_ExpenseExampleYear10

3,906

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

367

3 Years

rr_ExpenseExampleNoRedemptionYear03

1,117

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,888

10 Years

rr_ExpenseExampleNoRedemptionYear10

3,906

Janus World Allocation Fund | Class A, C, S, I, T Shares | Class S

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class S

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class S

Management Fees

rr_ManagementFeesOverAssets

0.07%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

1.96%

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.74%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

3.02%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

1.31%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.71%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleYear01

305

3 Years

rr_ExpenseExampleYear03

933

5 Years

rr_ExpenseExampleYear05

1,587

10 Years

rr_ExpenseExampleYear10

3,337

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

305

3 Years

rr_ExpenseExampleNoRedemptionYear03

933

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,587

10 Years

rr_ExpenseExampleNoRedemptionYear10

3,337

Janus World Allocation Fund | Class A, C, S, I, T Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class I

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class I

Management Fees

rr_ManagementFeesOverAssets

0.07%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

1.76%

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.74%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

2.57%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

1.36%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.21%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleYear01

260

3 Years

rr_ExpenseExampleYear03

799

5 Years

rr_ExpenseExampleYear05

1,365

10 Years

rr_ExpenseExampleYear10

2,905

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

260

3 Years

rr_ExpenseExampleNoRedemptionYear03

799

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,365

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,905

2009

rr_AnnualReturn2009

28.87%

2010

rr_AnnualReturn2010

11.54%

2011

rr_AnnualReturn2011

(8.00%)

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

8.19%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

14.90%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(13.38%)

Janus World Allocation Fund | Class A, C, S, I, T Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class T

Management Fees

rr_ManagementFeesOverAssets

0.07%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

1.89%

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.74%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

2.70%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

1.24%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

1.46%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleYear01

273

3 Years

rr_ExpenseExampleYear03

838

5 Years

rr_ExpenseExampleYear05

1,430

10 Years

rr_ExpenseExampleYear10

3,032

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

273

3 Years

rr_ExpenseExampleNoRedemptionYear03

838

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,430

10 Years

rr_ExpenseExampleNoRedemptionYear10

3,032

Janus World Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class A

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class A Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[2]

1 Year

rr_AverageAnnualReturnYear01

(13.24%)

Since Inception

rr_AverageAnnualReturnSinceInception

(1.79%)

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 03, 2008

Janus World Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class C

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class C Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[3]

1 Year

rr_AverageAnnualReturnYear01

(9.46%)

Since Inception

rr_AverageAnnualReturnSinceInception

(0.62%)

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 03, 2008

Janus World Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class S

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class S Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(8.07%)

Since Inception

rr_AverageAnnualReturnSinceInception

(0.19%)

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 03, 2008

Janus World Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(8.00%)

Since Inception

rr_AverageAnnualReturnSinceInception

0.06%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 03, 2008

Janus World Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(7.87%)

Since Inception

rr_AverageAnnualReturnSinceInception

0.03%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 03, 2008

Janus World Allocation Fund | Class A, C, S, I, T Shares | Return After Taxes on Distributions | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

(9.03%)

Since Inception

rr_AverageAnnualReturnSinceInception

(0.71%)

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 03, 2008

Janus World Allocation Fund | Class A, C, S, I, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[4]

1 Year

rr_AverageAnnualReturnYear01

(4.11%)

Since Inception

rr_AverageAnnualReturnSinceInception

(0.15%)

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 03, 2008

Janus World Allocation Fund | Class A, C, S, I, T Shares | Morgan Stanley Capital International All Country World Index (net of foreign withholding taxes) (reflects no deduction for expenses, fees, or taxes, except foreign withholding taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Morgan Stanley Capital International All Country World Index^sm (net of foreign withholding taxes)

1 Year

rr_AverageAnnualReturnYear01

(7.35%)

Since Inception

rr_AverageAnnualReturnSinceInception

(0.71%)

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 03, 2008

Janus World Allocation Fund | Class A, C, S, I, T Shares | World Allocation Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

World Allocation Index

1 Year

rr_AverageAnnualReturnYear01

(2.72%)

Since Inception

rr_AverageAnnualReturnSinceInception

2.25%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 03, 2008

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding any expenses of an underlying fund (acquired fund fees and expenses), the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, and Class S Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees for Class A Shares, Class C Shares, and Class I Shares); brokerage commissions; interest; dividends; taxes; and extraordinary expenses) to 0.45% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

[4] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	JANUS INVESTMENT FUND
Prospectus Date	rr_ProspectusDate	Oct. 26, 2012
Document Creation Date	dei_DocumentCreationDate	Oct. 25, 2012

XML

Janus Conservative Allocation Fund | Class D Shares

Fund summary

Janus Conservative Allocation Fund

INVESTMENT OBJECTIVE

Janus Conservative Allocation Fund seeks total return through a primary emphasis on income with a secondary emphasis on growth of capital.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses		Janus Conservative Allocation Fund Class D Shares Class D
Operating Expenses Column [Text]		Class D
Management Fees		0.05%
Other Expenses	[1]	0.22%
Acquired Fund Fees and Expenses		0.64%
Total Annual Fund Operating Expenses		0.91%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses (including the operating expenses of the underlying funds) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Janus Conservative Allocation Fund Class D Shares Class D	Class D Shares	93	290	504	1,120

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 10% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund seeks to achieve its investment objective by investing in other Janus mutual funds (“underlying funds”) that represent a variety of asset classes and investment styles. The Fund pursues this objective by investing in a diversified portfolio of underlying funds resulting in an allocation of the Fund’s investments that normally provides exposure of approximately 40% to stocks and 60% to bonds and money market securities. The target allocation and the allocation of the Fund’s assets among underlying funds are based on quantitative and qualitative analysis. Because it invests in other funds, the Fund is considered a “fund of funds.”

The Fund’s asset allocation is intended to diversify investments among stocks, bonds, and cash equivalents. The portfolio manager regularly reviews the allocation of Fund assets in the underlying funds and may modify the underlying funds’ weightings or substitute other underlying funds to emphasize and mitigate risk exposures that may arise as a result of the implementation of the allocations. An independent asset allocation service provides evaluations of asset allocations that the portfolio manager may use in implementing the allocations among the underlying funds. The portfolio manager continually monitors asset class allocations and periodically rebalances the Fund’s investments in the underlying funds. The portfolio manager may change the Fund’s asset class allocations, the underlying funds, an underlying fund’s asset category, or weightings among asset classes or underlying funds without prior shareholder notice.

The Fund will normally allocate approximately 60% of its investments to underlying bond funds and money market instruments; and approximately 40% of its investments to underlying funds that provide varying exposure to common stocks of large U.S.-based companies, small- to mid-capitalization companies, and international companies (including those with exposure to emerging markets). Refer to Appendix A in this Prospectus for a brief description of the investment strategies of each of the currently available underlying funds.

When market conditions dictate a more defensive strategy, the Fund or an underlying fund may temporarily hold cash or invest its assets in temporary investments. In that case, the Fund may take positions that are inconsistent with its investment objective. As a result, the Fund may not achieve its investment objective.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking income and, to a lesser extent, growth of capital. Investments in a portfolio with common stock exposure tend to be more volatile than many other investment choices.

Main Risks Associated with the Fund
Allocation Risk. The Fund’s ability to achieve its investment objective depends largely upon the portfolio manager’s allocation of assets among the underlying funds and other securities, using the optimization process (a process that utilizes quantitative analysis of a number of factors, such as historical risk, performance, fund classifications, and the relationship among underlying funds) and the judgment of the portfolio manager. You could lose money on your investment in the Fund as a result of these allocations. The Fund will typically invest in a number of different underlying funds; however, to the extent that the Fund invests a significant portion of its assets in a single underlying fund, it will be more sensitive to the risks associated with that fund and any investments in which that fund concentrates.

Affiliated Fund Risk. Janus Capital has the authority to select and substitute underlying affiliated mutual funds. The fees paid to Janus Capital by some Janus mutual funds are generally higher than the fees paid to Janus Capital by the Fund or by other funds and share classes available for investment by the Fund. These conditions may create a conflict of interest when selecting underlying affiliated mutual funds and share classes for investment. Janus Capital, however, is a fiduciary to the Fund and its shareholders and is legally obligated to act in their best interest when selecting underlying affiliated mutual funds.

Main Risks Associated with the Underlying Funds and Securities
The biggest risk is that the underlying funds’ returns will vary, and you could lose money.

Fixed-Income Securities Risk. Approximately 60% of the Fund’s assets are allocated to fixed-income securities through investments in underlying funds. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause an underlying fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which an underlying fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that an underlying fund’s portfolio manager would like or at the price that the portfolio manager believes the security is currently worth.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Market Risk. Approximately 40% of the Fund’s assets are allocated to equity investments through investments in underlying funds. The value of an underlying fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if a portfolio manager’s belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of an underlying fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Foreign Exposure Risk. Certain underlying funds may have significant exposure to foreign markets as a result of their investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, an underlying fund’s returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. A market swing in one or more countries or regions where an underlying fund has invested a significant amount of its assets may have a greater effect on an underlying fund’s performance than it would in a more geographically diversified portfolio. An underlying fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Emerging Markets Risk. The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities involve a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. In addition, an underlying fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of an underlying fund’s investments. To the extent that an underlying fund invests a significant portion of its assets in the securities of issuers in or companies of a single country or region, it is more likely to be impacted by events or conditions affecting that country or region, which could have a negative impact on the Fund’s performance. Some of the risks of investing directly in foreign and emerging market securities may be reduced when an underlying fund invests indirectly in foreign securities through various other investment vehicles including derivatives, which also involve other risks.

Sovereign Debt Risk. An underlying fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

Exchange-Traded Funds Risk. Certain underlying funds may purchase shares of exchange-traded funds (“ETFs”) to gain exposure to a particular portion of the market. ETFs are pooled investment vehicles, which may be managed or unmanaged, that generally seek to track the performance of a specific index. ETFs are traded on an exchange at market prices that may vary from the net asset value of their underlying investments. When an underlying fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF’s expenses. ETFs have certain inherent risks generally associated with investments in a portfolio of securities in which the ETF is invested, including the risk that the general level of stock prices may decline, thereby adversely affecting the value of each unit of the ETF. ETFs also involve the risk that an active trading market for an ETF’s shares may not develop or be maintained.

Exchange-Traded Notes Risk. Certain underlying funds may invest in exchange-traded notes (“ETNs”), which are debt securities whose returns are linked to a particular index. ETNs are typically linked to the performance of a commodities index that reflects the potential return on unleveraged investments in futures contracts of physical commodities, plus a specified rate of interest that could be earned on cash collateral. ETNs are subject to credit risk. The value of an ETN may vary and may be influenced by time to maturity, level of supply and demand for the ETN, volatility and lack of liquidity in underlying commodities markets, changes in the applicable interest rates, changes in the issuer’s credit rating, and economic, legal, political, or geographic events that affect the referenced commodity. When an underlying fund invests in ETNs it will bear its proportionate share of any fees and expenses borne by the ETN. There may be restrictions on an underlying fund’s right to redeem its investment in an ETN, which is meant to be held until maturity. An underlying fund’s decision to sell its ETN holdings may be limited by the availability of a secondary market.

Derivatives Risk. Certain underlying funds may invest in derivatives. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares, the predecessor share class. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses in effect during the periods shown, net of any applicable fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. Performance information for each underlying fund is available in its prospectus and/or the most recent annual or semiannual report. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Annual Total Returns for Class D Shares (calendar year-end)

Best Quarter:  Second Quarter 2009  10.64%          Worst Quarter:  Third Quarter 2008  −6.58%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 9.32%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Janus Conservative Allocation Fund Class D Shares	Column	Label		1 Year	5 Years	Since Inception	Inception Date
Class D Return Before Taxes	Class D Shares	Return Before Taxes		1.51%	5.11%	6.08%	Dec. 30, 2005
Class D Return After Taxes on Distributions	Class D Shares	Return After Taxes on Distributions		0.54%	4.00%	5.03%	Dec. 30, 2005
Class D Return After Taxes on Distributions and Sale of Fund Shares	Class D Shares	Return After Taxes on Distributions and Sale of Fund Shares	[1]	1.07%	3.76%	4.66%	Dec. 30, 2005
S&P 500 Index (reflects no deduction for expenses, fees, or taxes)		S&P 500® Index		2.11%	(0.25%)	2.26%	Dec. 30, 2005
Conservative Allocation Index (reflects no deduction for expenses, fees, or taxes)		Conservative Allocation Index		3.61%	3.89%	4.89%	Dec. 30, 2005

The Conservative Allocation Index is an internally-calculated, hypothetical combination of unmanaged indices that combines total returns from the Barclays U.S. Aggregate Bond Index (60%), the Dow Jones Wilshire 5000 Index (28%), and the Morgan Stanley Capital International Europe, Australasia, Far East Index (“MSCI EAFE^®”) Index (12%).

After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; and for the Fund’s Class J Shares, the predecessor share class, for the periods prior to February 16, 2010. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

[1] Other Expenses are based on the estimated expenses that the Fund expects to incur.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

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INTECH Global Dividend Fund | Class D Shares

Fund summary

INTECH Global Dividend Fund

INVESTMENT OBJECTIVE

INTECH Global Dividend Fund seeks long-term growth of capital and income.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES
    (expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses

INTECH Global Dividend Fund

Class D Shares

Class D

Operating Expenses Column [Text]

Class D

Management Fees

0.55%

Other Expenses

5.60%

Total Annual Fund Operating Expenses

^[1]

6.15%

Fee Waiver

^[1]

5.34%

Total Annual Fund Operating Expenses After Fee Waiver

^[1]

0.81%

EXAMPLE:

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers or recoupments (if applicable) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)

Expense Example, By Year, Column [Text]

1 Year

3 Years

5 Years

10 Years

INTECH Global Dividend Fund Class D Shares Class D

Class D Shares

611

1,813

2,988

5,808

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the period December 15, 2011 to June 30, 2012, the Fund’s portfolio turnover rate was 24% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund invests, under normal circumstances, at least 80% of its net assets in dividend-paying securities. The Fund invests primarily in common stocks from the universe of the Morgan Stanley Capital International (“MSCI”) World High Dividend Yield Index, utilizing INTECH’s mathematical investment process. The MSCI World High Dividend Yield Index is designed to reflect the performance of the high dividend yield securities contained within the broader MSCI World Index^sm. The Fund may also invest in foreign equity and debt securities.

The Fund pursues its investment objective by applying a mathematical investment process to construct an investment portfolio from the universe of common stocks within its named benchmark index. The goal of this process is to build a portfolio of stocks in a more efficient combination than the named benchmark index. The process seeks to capitalize on the natural volatility of the market by searching for stocks within the index that have high relative volatility (providing the potential for excess returns) but that essentially move in opposite directions or have low correlation to each other (providing the potential for lower relative risk). By constructing the portfolio in this manner and periodically rebalancing the portfolio to maintain potentially more efficient weightings, INTECH’s mathematical investment process seeks to create a portfolio that, over time, produces returns in excess of its named benchmark index with risks similar to that of the benchmark index. The rebalancing techniques used by INTECH may result in a higher portfolio turnover compared to a “buy and hold” fund strategy.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Foreign Exposure Risk. The Fund normally has significant exposure to foreign markets as a result of its investments in foreign securities, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio.

Dividend Risk. Companies that issue dividend-yielding securities are not required to continue to pay dividends on such securities. Therefore, there is the possibility that such companies could reduce or eliminate the payment of dividends in the future.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Investment Process Risk. The proprietary mathematical investment process used by INTECH may not achieve the desired results. On an occasional basis, INTECH considers changes to its mathematical investment process. These changes may result in changes to the portfolio, might not provide the intended results, and may adversely impact the Fund’s performance.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The Fund does not have a full calendar year of operations. Performance information for certain periods is included in the Fund’s first annual and/or semiannual report.

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding administrative services fees payable pursuant to the Transfer Agency Agreement, brokerage commissions, interest, dividends, taxes, acquired fund fees and expenses, and extraordinary expenses) to 0.50% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees. For a period of three years subsequent to the Fund's commencement of operations (December 15, 2011), Janus Capital may recover from the Fund fees and expenses previously waived or reimbursed, which could then be considered a deferral, if the Fund's expense ratio, including recovered expenses, falls below the expense limit.

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Label

Element

Value

Risk/Return:

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Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

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Oct. 26, 2012

Janus Global Bond Fund | Class D Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

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Fund summary

Janus Global Bond Fund

Objective [Heading]

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INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Janus Global Bond Fund seeks total return, consistent with preservation of capital.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

November 1, 2013

Portfolio Turnover [Heading]

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Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 222% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

222.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

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The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers or recoupments (if applicable) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund pursues its investment objective by investing, under normal circumstances, at least 80% of its net assets in bonds. Bonds include, but are not limited to, corporate bonds, government notes and bonds, convertible bonds, mortgage-backed securities, and zero-coupon bonds. The Fund invests in corporate debt securities of issuers in a number of different countries, which may include the United States. The Fund invests in securities of issuers located in developed and emerging market countries. The Fund may invest across all fixed-income sectors, including U.S. and non-U.S. government securities. The Fund’s investments may be denominated in local currency or U.S. dollar-denominated. The Fund may invest in debt securities with a range of maturities from short- to long-term. The Fund may invest up to 35% of its net assets in high-yield/high-risk debt securities. The Fund may also invest in preferred and common stock, money market instruments, municipal bonds, commercial and residential mortgage-backed securities, asset-backed securities, other securitized and structured debt products, private placements, and other investment companies, including exchange-traded funds (“ETFs”). The Fund may also invest in bank loans, euro-denominated obligations, buy backs or dollar rolls, when-issued securities, and reverse repurchase agreements. Due to the nature of securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

In addition, the Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices, as substitutes for securities in which the Fund invests. The Fund has invested in and is expected to continue to invest in collateralized forward foreign currency exchange contracts, futures, options, and swaps (including interest rate swaps, total return swaps, and credit default swaps) for hedging purposes (to offset risks associated with an investment, currency exposure, or market conditions) and to increase or decrease the Fund’s exposure to a particular market, to manage or adjust the risk profile of the Fund related to an investment or currency exposure, to adjust its currency exposure relative to its benchmark index, and to earn income and enhance returns. In particular, the Fund may use interest rate futures to manage portfolio risk. The Fund’s exposure to derivatives will vary, is not limited to those derivatives listed, and could be significant at times. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

In addition to considering economic factors such as the effect of interest rates on the Fund’s investments, the portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income-producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

Foreign Exposure Risk. The Fund normally has significant exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries. To the extent the Fund invests in foreign debt securities, such investments are sensitive to changes in interest rates. Additionally, investments in securities of foreign governments involve the risk that a foreign government may not be willing or able to pay interest or repay principal when due.

Eurozone Exposure Risk. The Fund’s investment may include certain securities that are denominated and traded in, or based on, the euro, the official currency of the Eurozone. European markets have recently experienced volatility and adverse trends due to concerns about economic downturns, rising government debt levels, and the possible default of government debt in several European countries, including Greece, Ireland, Italy, Portugal, and Spain. A default or debt restructuring by any European country would adversely impact holders of that country’s debt and worldwide sellers of credit default swaps linked to that country’s creditworthiness. These trends have adversely affected the value and exchange rate of the euro and may continue to significantly affect the economies of all European countries, which in turn may have a material adverse affect on a Fund’s investments in such countries, other countries that depend on European countries for significant amounts of trade or investment, or issuers with exposure to European debt.

Emerging Markets Risk. The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities involve a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. There is a risk in developing countries that a future economic or political crisis could lead to price controls, forced mergers of companies, expropriation or confiscatory taxation, seizure, nationalization, or creation of government monopolies, any of which may have a detrimental effect on the Fund’s investments. In addition, the Fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of the Fund’s investments. To the extent that the Fund invests a significant portion of its assets in the securities of issuers in or companies of a single country or region, it is more likely to be impacted by events or conditions affecting that country or region, which could have a negative impact on the Fund’s performance. Some of the risks of investing directly in foreign and emerging market securities may be reduced when the Fund invests indirectly in foreign securities through various other investment vehicles including derivatives, which also involve other risks. As of June 30, 2012, approximately 10.1% of the Fund’s investments were in emerging markets.

Sovereign Debt Risk. The Fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However, investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner. A sovereign debtor’s willingness or ability to satisfy its debt obligation may be affected by various factors including, but not limited to, its cash flow situation, the extent of its foreign currency reserves, the availability of foreign exchange when a payment is due, and the relative size of its debt position in relation to its economy as a whole. In the event of default, there may be limited or no legal remedies for collecting sovereign debt and there may be no bankruptcy proceedings through which the Fund may collect all or part of the sovereign debt that a governmental entity has not repaid.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

High-Yield/High-Risk Bond Risk. High-yield/high-risk bonds (also known as “junk bonds”) may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Bank Loan Risk. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. Participation interests and assignments involve credit, interest rate, and liquidity risk. In addition, the bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings.

Exchange-Traded Funds Risk. The Fund may purchase shares of exchange-traded funds (“ETFs”) to gain exposure to a particular portion of the market. ETFs are pooled investment vehicles, which may be managed or unmanaged, that generally seek to track the performance of a specific index. ETFs are traded on an exchange at market prices that may vary from the net asset value of their underlying investments. When the Fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF’s expenses. ETFs have certain inherent risks generally associated with investments in a portfolio of securities in which the ETF is invested, including the risk that the general level of stock prices may decline, thereby adversely affecting the value of each unit of the ETF. ETFs also involve the risk that an active trading market for an ETF’s shares may not develop or be maintained.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. The bar chart depicts the Fund’s performance during the period indicated. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the Fund’s performance during the period indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-800-525-3713

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/allfunds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class D Shares (calendar year-end)

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Second Quarter 2011  2.84%          Worst Quarter:  Third Quarter 2011  0.60%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund's year-to-date return as of the calendar quarter ended September 30, 2012 was 7.82%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Janus Global Bond Fund | Class D Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class D

Management Fees

rr_ManagementFeesOverAssets

0.60%

Other Expenses

rr_OtherExpensesOverAssets

0.71%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.31%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.40%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.91%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class D Shares

1 Year

rr_ExpenseExampleYear01

133

3 Years

rr_ExpenseExampleYear03

415

5 Years

rr_ExpenseExampleYear05

718

10 Years

rr_ExpenseExampleYear10

1,579

2011

rr_AnnualReturn2011

6.65%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

7.82%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2011

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

2.84%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

0.60%

Janus Global Bond Fund | Class D Shares | Return Before Taxes | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

6.65%

Since Inception

rr_AverageAnnualReturnSinceInception

6.59%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 28, 2010

Janus Global Bond Fund | Class D Shares | Return After Taxes on Distributions | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

5.31%

Since Inception

rr_AverageAnnualReturnSinceInception

5.26%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 28, 2010

Janus Global Bond Fund | Class D Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

1 Year

rr_AverageAnnualReturnYear01

4.33%

Since Inception

rr_AverageAnnualReturnSinceInception

4.85%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 28, 2010

Janus Global Bond Fund | Class D Shares | Barclays Global Aggregate Bond Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Barclays Global Aggregate Bond Index

1 Year

rr_AverageAnnualReturnYear01

5.64%

Since Inception

rr_AverageAnnualReturnSinceInception

7.16%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 28, 2010

Janus Global Bond Fund | Class D Shares | Barclays Global Aggregate Corporate Bond Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Barclays Global Aggregate Corporate Bond Index

1 Year

rr_AverageAnnualReturnYear01

4.32%

Since Inception

rr_AverageAnnualReturnSinceInception

6.05%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 28, 2010

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding administrative services fees payable pursuant to the Transfer Agency Agreement, brokerage commissions, interest, dividends, taxes, acquired fund fees and expenses, and extraordinary expenses) to 0.75% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees. For a period of three years subsequent to the Fund's commencement of operations (December 28, 2010) or until the Fund's assets exceed the first breakpoint in the investment advisory fee schedule, whichever occurs first, Janus Capital may recover from the Fund fees and expenses previously waived or reimbursed, which could then be considered a deferral, if the Fund's expense ratio, including recovered expenses, falls below the expense limit.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Janus Short-Term Bond Fund | Class D Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Janus Short-Term Bond Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Janus Short-Term Bond Fund seeks as high a level of current income as is consistent with preservation of capital.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

November 1, 2013

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 93% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

93.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund invests, under normal circumstances, at least 80% of its net assets in short- and intermediate-term securities such as corporate bonds or notes or government securities, including agency securities. The Fund may invest up to 35% of its net assets in high-yield/high risk bonds, also known as “junk bonds.” The Fund expects to maintain an average-weighted effective maturity of three years or less under normal circumstances. As of June 30, 2012, the Fund’s weighted average maturity was 2.4 years. The Fund may also invest in bank loans, mortgage-backed securities, asset-backed securities, and foreign debt securities (which may include investments in emerging markets). Due to the nature of securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

“Effective” maturity differs from actual maturity, which may be longer. In calculating the “effective” maturity the portfolio managers will estimate the effect of expected principal payments and call provisions on securities held in the portfolio. This gives the portfolio managers some additional flexibility in the securities they purchase, but all else being equal, could result in more volatility than if the Fund calculated an actual maturity target.

In addition, the Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. In particular, the Fund may use interest rate futures to manage portfolio risk. The Fund’s exposure to derivatives will vary. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

In addition to considering economic factors such as the effect of interest rates on the Fund’s investments, the portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income-producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

Sovereign Debt Risk. The Fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However, investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Bank Loan Risk. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. Participation interests and assignments involve credit, interest rate, and liquidity risk. In addition, the bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. To the extent the Fund invests in foreign debt securities, such investments are sensitive to changes in interest rates. Additionally, investments in securities of foreign governments involve the risk that a foreign government may not be willing or able to pay interest or repay principal when due. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

High-Yield/High-Risk Bond Risk. High-yield/high-risk bonds may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares, the predecessor share class. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses in effect during the periods shown, net of any applicable fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-800-525-3713

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/allfunds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class D Shares (calendar year-end)

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Second Quarter 2009  3.18%          Worst Quarter:  Second Quarter 2008  −0.90%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 3.05%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; and for the Fund’s Class J Shares, the predecessor share class, for the periods prior to February 16, 2010. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Janus Short-Term Bond Fund | Class D Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class D

Management Fees

rr_ManagementFeesOverAssets

0.55%

Other Expenses

rr_OtherExpensesOverAssets

0.19%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.74%

^[1]

Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.05%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver

rr_NetExpensesOverAssets

0.69%

^[1]

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class D Shares

1 Year

rr_ExpenseExampleYear01

76

3 Years

rr_ExpenseExampleYear03

237

5 Years

rr_ExpenseExampleYear05

411

10 Years

rr_ExpenseExampleYear10

918

2002

rr_AnnualReturn2002

3.57%

2003

rr_AnnualReturn2003

3.91%

2004

rr_AnnualReturn2004

1.96%

2005

rr_AnnualReturn2005

1.52%

2006

rr_AnnualReturn2006

4.21%

2007

rr_AnnualReturn2007

5.21%

2008

rr_AnnualReturn2008

4.63%

2009

rr_AnnualReturn2009

8.56%

2010

rr_AnnualReturn2010

3.48%

2011

rr_AnnualReturn2011

1.50%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

3.05%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

3.18%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Jun. 30, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(0.90%)

Janus Short-Term Bond Fund | Class D Shares | Return Before Taxes | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

1.50%

5 Years

rr_AverageAnnualReturnYear05

4.65%

10 Years

rr_AverageAnnualReturnYear10

3.83%

Since Inception

rr_AverageAnnualReturnSinceInception

4.65%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 01, 1992

Janus Short-Term Bond Fund | Class D Shares | Return After Taxes on Distributions | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

0.66%

5 Years

rr_AverageAnnualReturnYear05

3.43%

10 Years

rr_AverageAnnualReturnYear10

2.63%

Since Inception

rr_AverageAnnualReturnSinceInception

2.93%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 01, 1992

Janus Short-Term Bond Fund | Class D Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[2]

1 Year

rr_AverageAnnualReturnYear01

1.01%

5 Years

rr_AverageAnnualReturnYear05

3.27%

10 Years

rr_AverageAnnualReturnYear10

2.58%

Since Inception

rr_AverageAnnualReturnSinceInception

2.90%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 01, 1992

Janus Short-Term Bond Fund | Class D Shares | Barclays 1-3 Year U.S. Government/Credit Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Barclays 1-3 Year U.S. Government/Credit Index

1 Year

rr_AverageAnnualReturnYear01

1.59%

5 Years

rr_AverageAnnualReturnYear05

3.99%

10 Years

rr_AverageAnnualReturnYear10

3.63%

Since Inception

rr_AverageAnnualReturnSinceInception

4.80%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 01, 1992

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding administrative services fees payable pursuant to the Transfer Agency Agreement, brokerage commissions, interest, dividends, taxes, acquired fund fees and expenses, and extraordinary expenses) to 0.55% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

[2] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Perkins Small Cap Value Fund | Class D Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Perkins Small Cap Value Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Perkins Small Cap Value Fund seeks capital appreciation.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 62% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

62.00%

Expense Example [Heading]

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EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

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The Fund pursues its investment objective by investing primarily in the common stocks of small companies whose stock prices are believed to be undervalued by the Fund’s portfolio managers. The Fund invests, under normal circumstances, at least 80% of its net assets in equity securities of small companies whose market capitalization, at the time of initial purchase, is less than the 12-month average of the maximum market capitalization for companies included in the Russell 2000^® Value Index. This average is updated monthly. The market capitalizations within the index will vary, but as of June 30, 2012, they ranged from approximately $85 million to $2.7 billion. The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets. The Fund may invest, under normal circumstances, up to 20% of its net assets in securities of companies having market capitalizations outside of the aforementioned market capitalization ranges. In addition, when the portfolio managers believe that market conditions are unfavorable for investing, or when they are otherwise unable to locate attractive investment opportunities, the Fund may invest up to 20% of its net assets in cash or similar investments.

The Fund’s securities selection focuses on companies that are out of favor with markets or have not yet been discovered by the broader investment community.

The Fund’s portfolio managers generally look for companies with:

• strong balance sheets and solid recurring free cash flows
• attractive relative and absolute valuation ratios or that have underperformed recently
• favorable reward to risk characteristics

The portfolio managers’ philosophy is to weigh a security’s downside risk before considering its upside potential, which may help provide an element of capital preservation.

Risk [Heading]

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PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

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The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s portfolio managers. When the Fund’s investments in cash or similar investments increase due to a lack of favorable investment opportunities or other extraordinary factors, the Fund may not participate in market advances or declines to the same extent that it would if the Fund had been fully invested.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Small-Sized Companies Risk. The Fund’s investments in securities issued by small-sized companies, which tend to be smaller, start-up companies offering emerging products or services, may involve greater risks than are customarily associated with larger, more established companies. Securities issued by small-sized companies tend to be more volatile and somewhat more speculative than securities issued by larger or more established companies and may underperform as compared to the securities of larger companies.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

The biggest risk is that the Fund’s returns will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

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PERFORMANCE INFORMATION

Performance Narrative [Text Block]

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The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares (formerly named Investor Shares). For the periods prior to April 21, 2003, the performance shown for Class D Shares reflects the historical performance of Berger Small Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Investor Shares into the Fund’s Class J Shares). If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-800-525-3713

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/allfunds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

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Annual Total Returns for Class D Shares (calendar year-end)

Bar Chart Closing [Text Block]

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Best Quarter:  Second Quarter 2009  23.04%          Worst Quarter:  Third Quarter 2002  −22.57%

Year to Date Return, Label

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The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 6.28%.

Performance Table Heading

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Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

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Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

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After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; for the Fund’s Class J Shares (formerly named Investor Shares) for the period April 21, 2003 to February 16, 2010; and for Berger Small Cap Value Fund – Investor Shares for periods prior to April 21, 2003. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Closing [Text Block]

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Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Perkins Small Cap Value Fund | Class D Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class D

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.75%

Other Expenses

rr_OtherExpensesOverAssets

0.20%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.95%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class D Shares

1 Year

rr_ExpenseExampleYear01

97

3 Years

rr_ExpenseExampleYear03

303

5 Years

rr_ExpenseExampleYear05

525

10 Years

rr_ExpenseExampleYear10

1,166

2002

rr_AnnualReturn2002

(15.59%)

2003

rr_AnnualReturn2003

36.78%

2004

rr_AnnualReturn2004

13.57%

2005

rr_AnnualReturn2005

8.90%

2006

rr_AnnualReturn2006

12.37%

2007

rr_AnnualReturn2007

2.97%

2008

rr_AnnualReturn2008

(21.79%)

2009

rr_AnnualReturn2009

36.59%

2010

rr_AnnualReturn2010

18.00%

2011

rr_AnnualReturn2011

(3.33%)

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

6.28%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

23.04%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2002

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(22.57%)

Perkins Small Cap Value Fund | Class D Shares | Return Before Taxes | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(3.33%)

5 Years

rr_AverageAnnualReturnYear05

4.64%

10 Years

rr_AverageAnnualReturnYear10

7.25%

Perkins Small Cap Value Fund | Class D Shares | Return After Taxes on Distributions | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

(5.81%)

5 Years

rr_AverageAnnualReturnYear05

2.91%

10 Years

rr_AverageAnnualReturnYear10

5.38%

Perkins Small Cap Value Fund | Class D Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class D

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class D Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[1]

1 Year

rr_AverageAnnualReturnYear01

(0.51%)

5 Years

rr_AverageAnnualReturnYear05

3.44%

10 Years

rr_AverageAnnualReturnYear10

5.75%

Perkins Small Cap Value Fund | Class D Shares | Russell 2000 Value Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Russell 2000^® Value Index

1 Year

rr_AverageAnnualReturnYear01

(5.50%)

5 Years

rr_AverageAnnualReturnYear05

(1.87%)

10 Years

rr_AverageAnnualReturnYear10

6.40%

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Janus Moderate Allocation Fund | Class A, C, S, I, T Shares

Fund summary

Janus Moderate Allocation Fund

INVESTMENT OBJECTIVE

Janus Moderate Allocation Fund seeks total return through growth of capital and income.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 45 of the Fund’s Prospectus and in the “Purchases” section on page 63 of the Fund’s Statement of Additional Information.

SHAREHOLDER FEES
(fees paid directly from your investment)

Shareholder Fees Janus Moderate Allocation Fund Class A, C, S, I, T Shares

Class A

Class C

Class S

Class I

Class T

Shareholder Fees Column [Text]

Class A

Class C

Class S

Class I

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

5.75%

none

none

none

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

none

1.00%

none

none

none

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses Janus Moderate Allocation Fund Class A, C, S, I, T Shares

Class A

Class C

Class S

Class I

Class T

Operating Expenses Column [Text]

Class A

Class C

Class S

Class I

Class T

Management Fees

0.05%

0.05%

0.05%

0.05%

0.05%

Distribution/Service (12b-1) Fees

0.25%

1.00%

0.25%

none

none

Other Expenses

^[1]

0.15%

0.24%

0.33%

0.16%

0.34%

Acquired Fund Fees and Expenses

0.69%

0.69%

0.69%

0.69%

0.69%

Total Annual Fund Operating Expenses

1.14%

1.98%

1.32%

0.90%

1.08%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses (including the operating expenses of the underlying funds) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

If Shares are redeemed:

Expense Example Janus Moderate Allocation Fund Class A, C, S, I, T Shares (USD $)

Expense Example, By Year, Column [Text]

1 Year

3 Years

5 Years

10 Years

Class A

Class A Shares

685

916

1,167

1,881

Class C

Class C Shares

301

621

1,068

2,306

Class S

Class S Shares

134

418

723

1,590

Class I

Class I Shares

92

287

498

1,108

Class T

Class T Shares

110

343

595

1,317

If Shares are not redeemed:

Expense Example, No Redemption Janus Moderate Allocation Fund Class A, C, S, I, T Shares (USD $)

Expense Example, No Redemption, By Year, Column [Text]

1 Year

3 Years

5 Years

10 Years

Class A

Class A Shares

685

916

1,167

1,881

Class C

Class C Shares

201

621

1,068

2,306

Class S

Class S Shares

134

418

723

1,590

Class I

Class I Shares

92

287

498

1,108

Class T

Class T Shares

110

343

595

1,317

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 18% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund seeks to achieve its investment objective by investing in other Janus mutual funds (“underlying funds”) that represent a variety of asset classes and investment styles. The Fund pursues this objective by investing in a diversified portfolio of underlying funds resulting in an allocation of the Fund’s investments that normally provides exposure of approximately 60% to stocks and 40% to bonds and money market securities. The target allocation and the allocation of the Fund’s assets among underlying funds are based on quantitative and qualitative analysis. Because it invests in other funds, the Fund is considered a “fund of funds.”

The Fund’s asset allocation is intended to diversify investments among stocks, bonds, and cash equivalents. The portfolio manager regularly reviews the allocation of Fund assets in the underlying funds and may modify the underlying funds’ weightings or substitute other underlying funds to emphasize and mitigate risk exposures that may arise as a result of the implementation of the allocations. An independent asset allocation service provides evaluations of asset allocations that the portfolio manager may use in implementing the allocations among the underlying funds. The portfolio manager continually monitors asset class allocations and periodically rebalances the Fund’s investments in the underlying funds. The portfolio manager may change the Fund’s asset class allocations, the underlying funds, an underlying fund’s asset category, or weightings among asset classes or underlying funds without prior shareholder notice.

The Fund will normally allocate approximately 60% of its investments to underlying funds that provide varying exposure to common stocks of large U.S.-based companies, small- to mid-capitalization companies, and international companies (including those with exposure to emerging markets); and approximately 40% of its investments to underlying bond funds and money market instruments. Refer to Appendix A in this Prospectus for a brief description of the investment strategies of each of the currently available underlying funds.

When market conditions dictate a more defensive strategy, the Fund or an underlying fund may temporarily hold cash or invest its assets in temporary investments. In that case, the Fund may take positions that are inconsistent with its investment objective. As a result, the Fund may not achieve its investment objective.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking growth of capital and income. Investments in a portfolio with common stock exposure tend to be more volatile than many other investment choices.

Main Risks Associated with the Fund
Allocation Risk. The Fund’s ability to achieve its investment objective depends largely upon the portfolio manager’s allocation of assets among the underlying funds and other securities, using the optimization process (a process that utilizes quantitative analysis of a number of factors, such as historical risk, performance, fund classifications, and the relationship among underlying funds) and the judgment of the portfolio manager. You could lose money on your investment in the Fund as a result of these allocations. The Fund will typically invest in a number of different underlying funds; however, to the extent that the Fund invests a significant portion of its assets in a single underlying fund, it will be more sensitive to the risks associated with that fund and any investments in which that fund concentrates.

Affiliated Fund Risk. Janus Capital has the authority to select and substitute underlying affiliated mutual funds. The fees paid to Janus Capital by some Janus mutual funds are generally higher than the fees paid to Janus Capital by the Fund or by other funds and share classes available for investment by the Fund. These conditions may create a conflict of interest when selecting underlying affiliated mutual funds and share classes for investment. Janus Capital, however, is a fiduciary to the Fund and its shareholders and is legally obligated to act in their best interest when selecting underlying affiliated mutual funds.

Main Risks Associated with the Underlying Funds and Securities
The biggest risk is that the underlying funds’ returns will vary, and you could lose money.

Market Risk. Approximately 60% of the Fund’s assets are allocated to equity investments through investments in underlying funds. The value of an underlying fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if a portfolio manager’s belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of an underlying fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Fixed-Income Securities Risk. Approximately 40% of the Fund’s assets are allocated to fixed-income securities through investments in underlying funds. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause an underlying fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which an underlying fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that an underlying fund’s portfolio manager would like or at the price that the portfolio manager believes the security is currently worth.

Foreign Exposure Risk. Certain underlying funds may have significant exposure to foreign markets as a result of their investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, an underlying fund’s returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. A market swing in one or more countries or regions where an underlying fund has invested a significant amount of its assets may have a greater effect on an underlying fund’s performance than it would in a more geographically diversified portfolio. An underlying fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Emerging Markets Risk. The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities involve a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. In addition, an underlying fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of an underlying fund’s investments. To the extent that an underlying fund invests a significant portion of its assets in the securities of issuers in or companies of a single country or region, it is more likely to be impacted by events or conditions affecting that country or region, which could have a negative impact on the Fund’s performance. Some of the risks of investing directly in foreign and emerging market securities may be reduced when an underlying fund invests indirectly in foreign securities through various other investment vehicles including derivatives, which also involve other risks.

Sovereign Debt Risk. An underlying fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Exchange-Traded Funds Risk. Certain underlying funds may purchase shares of exchange-traded funds (“ETFs”) to gain exposure to a particular portion of the market. ETFs are pooled investment vehicles, which may be managed or unmanaged, that generally seek to track the performance of a specific index. ETFs are traded on an exchange at market prices that may vary from the net asset value of their underlying investments. When an underlying fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF’s expenses. ETFs have certain inherent risks generally associated with investments in a portfolio of securities in which the ETF is invested, including the risk that the general level of stock prices may decline, thereby adversely affecting the value of each unit of the ETF. ETFs also involve the risk that an active trading market for an ETF’s shares may not develop or be maintained.

Exchange-Traded Notes Risk. Certain underlying funds may invest in exchange-traded notes (“ETNs”), which are debt securities whose returns are linked to a particular index. ETNs are typically linked to the performance of a commodities index that reflects the potential return on unleveraged investments in futures contracts of physical commodities, plus a specified rate of interest that could be earned on cash collateral. ETNs are subject to credit risk. The value of an ETN may vary and may be influenced by time to maturity, level of supply and demand for the ETN, volatility and lack of liquidity in underlying commodities markets, changes in the applicable interest rates, changes in the issuer’s credit rating, and economic, legal, political, or geographic events that affect the referenced commodity. When an underlying fund invests in ETNs it will bear its proportionate share of any fees and expenses borne by the ETN. There may be restrictions on an underlying fund’s right to redeem its investment in an ETN, which is meant to be held until maturity. An underlying fund’s decision to sell its ETN holdings may be limited by the availability of a secondary market.

Derivatives Risk. Certain underlying funds may invest in derivatives. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares, the initial share class) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund commenced operations on July 6, 2009.

• The performance shown for Class T Shares is calculated using the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class A Shares, Class C Shares, and Class S Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers.
• The performance shown for Class I Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers.

If Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund had been available during periods prior to July 6, 2009, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, and Class I Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. Performance information for each underlying fund is available in its prospectus and/or the most recent annual or semiannual report. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Annual Total Returns for Class T Shares (calendar year-end)

Best Quarter:  Second Quarter 2009  14.27%        Worst Quarter:  Fourth Quarter 2008  −11.62%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 10.26%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Janus Moderate Allocation Fund Class A, C, S, I, T Shares

Column

Label

1 Year

5 Years

Since Inception

Inception Date

Class T Shares Return Before Taxes

Class T Shares

Return Before Taxes

(2.61%)

3.70%

5.39%

Dec. 30, 2005

Class T Shares Return After Taxes on Distributions

Class T Shares

Return After Taxes on Distributions

(3.32%)

2.81%

4.55%

Dec. 30, 2005

Class T Shares Return After Taxes on Distributions and Sale of Fund Shares

Class T Shares

Return After Taxes on Distributions and Sale of Fund Shares

^[1]

(1.57%)

2.71%

4.22%

Dec. 30, 2005

Class A Shares Return Before Taxes

Class A Shares

Return Before Taxes

^[2]

(8.26%)

2.33%

4.19%

Dec. 30, 2005

Class C Shares Return Before Taxes

Class C Shares

Return Before Taxes

^[3]

(4.34%)

2.80%

4.46%

Dec. 30, 2005

Class S Shares Return Before Taxes

Class S Shares

Return Before Taxes

(2.93%)

3.30%

4.97%

Dec. 30, 2005

Class I Shares Return Before Taxes

Class I Shares

Return Before Taxes

(2.47%)

3.70%

5.39%

Dec. 30, 2005

S&P 500 Index (reflects no deduction for expenses, fees, or taxes)

S&P 500^® Index

2.11%

(0.25%)

2.26%

Dec. 30, 2005

Moderate Allocation Index (reflects no deduction for expenses, fees, or taxes)

Moderate Allocation Index

0.96%

2.43%

4.16%

Dec. 30, 2005

The Moderate Allocation Index is an internally-calculated, hypothetical combination of unmanaged indices that combines total returns from the Dow Jones Wilshire 5000 Index (40%), the Barclays U.S. Aggregate Bond Index (40%), the MSCI EAFE^® Index (18%), and the Morgan Stanley Capital International Emerging Markets Free Index^sm (2%).

After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares, the initial share class). After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

[1] Other Expenses are based on the estimated expenses that the Fund expects to incur.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

[2] Calculated assuming maximum permitted sales loads.

[3] The one year return is calculated to include the contingent deferred sales charge.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

INTECH U.S. Growth Fund | Class A, C, S, I, T Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

INTECH U.S. Growth Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

INTECH U.S. Growth Fund seeks long-term growth of capital.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

SHAREHOLDER FEES
(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 84% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

84.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the "Purchases" section on page 46 of the Fund's Prospectus and in the "Purchases" section on page 83 of the Fund's Statement of Additional Information.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

If Shares are redeemed:

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

If Shares are not redeemed:

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund invests, under normal circumstances, at least 80% of its net assets in U.S. common stocks from the universe of the Russell 1000^® Growth Index, utilizing INTECH's mathematical investment process. The Russell 1000^® Growth Index is an unmanaged index that measures the performance of those Russell 1000 companies with higher price-to-book ratios and higher forecasted growth values.

The Fund pursues its investment objective by applying a mathematical investment process to construct an investment portfolio from the universe of common stocks within its named benchmark index. The goal of this process is to build a portfolio of stocks in a more efficient combination than the named benchmark index. The process seeks to capitalize on the natural volatility of the market by searching for stocks within the index that have high relative volatility (providing the potential for excess returns) but that essentially move in opposite directions or have low correlation to each other (providing the potential for lower relative risk). By constructing the portfolio in this manner and periodically rebalancing the portfolio to maintain potentially more efficient weightings, INTECH's mathematical investment process seeks to create a portfolio that, over time, produces returns in excess of its named benchmark index with risks similar to that of the benchmark index. The rebalancing techniques used by INTECH may result in a higher portfolio turnover compared to a "buy and hold" fund strategy.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The biggest risk is that the Fund's returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Growth Securities Risk. Securities of companies perceived to be "growth" companies may be more volatile than other stocks and may involve special risks. If a company's growth potential is not realized, the securities purchased may not perform as expected, reducing the Fund's returns. In addition, because different types of stocks tend to shift in and out of favor depending on market and economic conditions, "growth" stocks may perform differently from the market as a whole and other types of securities.

Market Risk. The value of the Fund's portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases. Further, regardless of how well individual companies or securities perform, the value of the Fund's portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Investment Process Risk. The proprietary mathematical investment process used by INTECH may not achieve the desired results. On an occasional basis, INTECH considers changes to its mathematical investment process. These changes may result in changes to the portfolio, might not provide the intended results, and may adversely impact the Fund's performance.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund's performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

The biggest risk is that the Fund's returns will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund's performance has varied over time. Class S Shares, Class A Shares, Class C Shares, and Class I Shares of the Fund commenced operations on July 6, 2009, after the reorganization of each corresponding class of shares of Janus Adviser INTECH Risk-Managed Growth Fund ("JAD predecessor fund") into each respective share class of the Fund. Class T Shares of the Fund commenced operations on July 6, 2009.

• The performance shown for Class S Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund's Class S Shares prior to the reorganization, calculated using the fees and expenses of the JAD predecessor fund's Class S Shares, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class A Shares reflects the performance of the JAD predecessor fund's Class A Shares from September 30, 2004 to July 6, 2009 (prior to the reorganization), calculated using the fees and expenses of Class A Shares of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers. Performance shown for certain periods prior to September 30, 2004 reflects the historical performance of the JAD predecessor fund's Class S Shares (formerly named Class I Shares), calculated using the fees and expenses of Class S Shares of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class C Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund's Class C Shares prior to the reorganization, calculated using the fees and expenses of the JAD predecessor fund's Class C Shares, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class I Shares reflects the performance of the JAD predecessor fund's Class I Shares from November 28, 2005 to July 6, 2009 (prior to the reorganization), calculated using the fees and expenses of Class I Shares of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers. Performance shown for certain periods prior to November 28, 2005 reflects the historical performance of the JAD predecessor fund's Class S Shares (formerly named Class I Shares), calculated using the fees and expenses of Class S Shares of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers.
• The performance shown for Class T Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund's Class S Shares prior to the reorganization, calculated using the fees and expenses of Class S Shares, net of any applicable fee and expense limitations or waivers.

If Class A Shares, Class I Shares, and Class T Shares of the Fund had been available during periods prior to July 6, 2009, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund's commencement of Class S Shares, Class A Shares, Class C Shares, Class I Shares, and Class T Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund's average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-877-335-2687

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/advisor/mutual-funds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class S Shares (calendar year-end)

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Second Quarter 2009  15.04%          Worst Quarter:  Fourth Quarter 2008   −25.11%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund's year-to-date return as of the calendar quarter ended September 30, 2012 was 16.23%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns are only shown for Class S Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class S Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

After-tax returns are calculated using distributions for the Fund's Class S Shares for periods following July 6, 2009; and for the JAD predecessor fund's Class S Shares (formerly named Class I Shares) for periods prior to July 6, 2009. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class S Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class S Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

INTECH U.S. Growth Fund | Class A, C, S, I, T Shares | Class A

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class A

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class A

Management Fees

rr_ManagementFeesOverAssets

0.50%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.17%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.92%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleYear01

663

3 Years

rr_ExpenseExampleYear03

851

5 Years

rr_ExpenseExampleYear05

1,055

10 Years

rr_ExpenseExampleYear10

1,641

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

663

3 Years

rr_ExpenseExampleNoRedemptionYear03

851

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,055

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,641

INTECH U.S. Growth Fund | Class A, C, S, I, T Shares | Class C

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class C

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

1.00%

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class C

Management Fees

rr_ManagementFeesOverAssets

0.50%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

0.21%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.71%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleYear01

274

3 Years

rr_ExpenseExampleYear03

539

5 Years

rr_ExpenseExampleYear05

928

10 Years

rr_ExpenseExampleYear10

2,019

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

174

3 Years

rr_ExpenseExampleNoRedemptionYear03

539

5 Years

rr_ExpenseExampleNoRedemptionYear05

928

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,019

INTECH U.S. Growth Fund | Class A, C, S, I, T Shares | Class S

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class S

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class S

Management Fees

rr_ManagementFeesOverAssets

0.50%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.32%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.07%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleYear01

109

3 Years

rr_ExpenseExampleYear03

340

5 Years

rr_ExpenseExampleYear05

590

10 Years

rr_ExpenseExampleYear10

1,306

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

109

3 Years

rr_ExpenseExampleNoRedemptionYear03

340

5 Years

rr_ExpenseExampleNoRedemptionYear05

590

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,306

2004

rr_AnnualReturn2004

12.34%

2005

rr_AnnualReturn2005

6.90%

2006

rr_AnnualReturn2006

6.90%

2007

rr_AnnualReturn2007

10.30%

2008

rr_AnnualReturn2008

(42.71%)

2009

rr_AnnualReturn2009

32.84%

2010

rr_AnnualReturn2010

17.50%

2011

rr_AnnualReturn2011

1.73%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

16.23%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

15.04%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(25.11%)

INTECH U.S. Growth Fund | Class A, C, S, I, T Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class I

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class I

Management Fees

rr_ManagementFeesOverAssets

0.50%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.12%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.62%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleYear01

63

3 Years

rr_ExpenseExampleYear03

199

5 Years

rr_ExpenseExampleYear05

346

10 Years

rr_ExpenseExampleYear10

774

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

63

3 Years

rr_ExpenseExampleNoRedemptionYear03

199

5 Years

rr_ExpenseExampleNoRedemptionYear05

346

10 Years

rr_ExpenseExampleNoRedemptionYear10

774

INTECH U.S. Growth Fund | Class A, C, S, I, T Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class T

Management Fees

rr_ManagementFeesOverAssets

0.50%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.33%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.83%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleYear01

85

3 Years

rr_ExpenseExampleYear03

265

5 Years

rr_ExpenseExampleYear05

460

10 Years

rr_ExpenseExampleYear10

1,025

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

85

3 Years

rr_ExpenseExampleNoRedemptionYear03

265

5 Years

rr_ExpenseExampleNoRedemptionYear05

460

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,025

INTECH U.S. Growth Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class A

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class A Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[1]

1 Year

rr_AverageAnnualReturnYear01

(3.80%)

5 Years

rr_AverageAnnualReturnYear05

(0.91%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

4.96%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jan. 02, 2003

INTECH U.S. Growth Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class C

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class C Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[2]

1 Year

rr_AverageAnnualReturnYear01

0.27%

5 Years

rr_AverageAnnualReturnYear05

(0.56%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

4.84%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jan. 02, 2003

INTECH U.S. Growth Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class S

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class S Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

1.73%

5 Years

rr_AverageAnnualReturnYear05

0.07%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

5.44%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jan. 02, 2003

INTECH U.S. Growth Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

2.23%

5 Years

rr_AverageAnnualReturnYear05

0.53%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

5.44%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jan. 02, 2003

INTECH U.S. Growth Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

2.03%

5 Years

rr_AverageAnnualReturnYear05

0.07%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

5.44%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jan. 02, 2003

INTECH U.S. Growth Fund | Class A, C, S, I, T Shares | Return After Taxes on Distributions | Class S

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class S Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

1.66%

5 Years

rr_AverageAnnualReturnYear05

(0.16%)

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

4.92%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jan. 02, 2003

INTECH U.S. Growth Fund | Class A, C, S, I, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class S

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class S Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[3]

1 Year

rr_AverageAnnualReturnYear01

1.22%

5 Years

rr_AverageAnnualReturnYear05

0.04%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

4.57%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jan. 02, 2003

INTECH U.S. Growth Fund | Class A, C, S, I, T Shares | Russell 1000 Growth Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Russell 1000^® Growth Index

1 Year

rr_AverageAnnualReturnYear01

2.64%

5 Years

rr_AverageAnnualReturnYear05

2.50%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

6.30%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jan. 02, 2003

[1] Calculated assuming maximum permitted sales loads.

[2] The one year return is calculated to include the contingent deferred sales charge.

[3] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Perkins Small Cap Value Fund | Class L Shares

Fund summary

Perkins Small Cap Value Fund

INVESTMENT OBJECTIVE

Perkins Small Cap Value Fund seeks capital appreciation.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses	Perkins Small Cap Value Fund Class L Shares Class L
Operating Expenses Column [Text]	Class L
Management Fees (may adjust up or down)	0.75%
Other Expenses	0.27%
Total Annual Fund Operating Expenses	1.02%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Perkins Small Cap Value Fund Class L Shares Class L	Class L Shares	104	325	563	1,248

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 62% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objective by investing primarily in the common stocks of small companies whose stock prices are believed to be undervalued by the Fund’s portfolio managers. The Fund invests, under normal circumstances, at least 80% of its net assets in equity securities of small companies whose market capitalization, at the time of initial purchase, is less than the 12-month average of the maximum market capitalization for companies included in the Russell 2000^® Value Index. This average is updated monthly. The market capitalizations within the index will vary, but as of June 30, 2012, they ranged from approximately $85 million to $2.7 billion. The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets. The Fund may invest, under normal circumstances, up to 20% of its net assets in securities of companies having market capitalizations outside of the aforementioned market capitalization ranges. In addition, when the portfolio managers believe that market conditions are unfavorable for investing, or when they are otherwise unable to locate attractive investment opportunities, the Fund may invest up to 20% of its net assets in cash or similar investments.

The Fund’s securities selection focuses on companies that are out of favor with markets or have not yet been discovered by the broader investment community.

The Fund’s portfolio managers generally look for companies with:

• strong balance sheets and solid recurring free cash flows
• attractive relative and absolute valuation ratios or that have underperformed recently
• favorable reward to risk characteristics

The portfolio managers’ philosophy is to weigh a security’s downside risk before considering its upside potential, which may help provide an element of capital preservation.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s portfolio managers. When the Fund’s investments in cash or similar investments increase due to a lack of favorable investment opportunities or other extraordinary factors, the Fund may not participate in market advances or declines to the same extent that it would if the Fund had been fully invested.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Small-Sized Companies Risk. The Fund’s investments in securities issued by small-sized companies, which tend to be smaller, start-up companies offering emerging products or services, may involve greater risks than are customarily associated with larger, more established companies. Securities issued by small-sized companies tend to be more volatile and somewhat more speculative than securities issued by larger or more established companies and may underperform as compared to the securities of larger companies.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund's performance has varied over time. The performance shown for periods following April 21, 2003, reflects the fees and expenses of Class L Shares (formerly named Institutional Shares), net of any applicable fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class L Shares reflects the historical performance of Berger Small Cap Value Fund – Institutional Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Institutional Shares into the Fund's Class L Shares).

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund's average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund's performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Annual Total Returns for Class L Shares (calendar year-end)

Best Quarter:  Second Quarter 2009  23.27%          Worst Quarter:  Third Quarter 2002  −22.47%

The Fund's year-to-date return as of the calendar quarter ended September 30, 2012 was 6.38%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Perkins Small Cap Value Fund Class L Shares	Column	Label		1 Year	5 Years	10 Years
Class L Return Before Taxes	Class L Shares	Return Before Taxes		(3.18%)	4.85%	7.48%
Class L Return After Taxes on Distributions	Class L Shares	Return After Taxes on Distributions		(5.68%)	3.09%	5.58%
Class L Return After Taxes on Distributions and Sale of Fund Shares	Class L Shares	Return After Taxes on Distributions and Sale of Fund Shares	[1]	(0.43%)	3.60%	5.93%
Russell 2000 Value Index (reflects no deduction for expenses, fees, or taxes)		Russell 2000® Value Index		(5.50%)	(1.87%)	6.40%

After-tax returns are calculated using distributions for the Fund's Class L Shares (formerly named Institutional Shares) for the periods following April 21, 2003 and for Berger Small Cap Value Fund – Institutional Shares for periods prior to April 21, 2003. If Class L Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

INTECH U.S. Core Fund | Class A, C, S, I, T Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

INTECH U.S. Core Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

INTECH U.S. Core Fund seeks long-term growth of capital.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

SHAREHOLDER FEES
(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 73% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

73.00%

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus mutual funds. More information about these and other discounts, as well as eligibility requirements for each share class, is available from your financial professional and in the “Purchases” section on page 46 of the Fund’s Prospectus and in the “Purchases” section on page 83 of the Fund’s Statement of Additional Information.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

50,000

Expense Example [Heading]

rr_ExpenseExampleHeading

EXAMPLE:

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

If Shares are redeemed:

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

If Shares are not redeemed:

Strategy [Heading]

rr_StrategyHeading

PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund invests, under normal circumstances, at least 80% of its net assets in U.S. common stocks from the universe of the S&P 500^® Index, utilizing INTECH’s mathematical investment process. The S&P 500^® Index is an unmanaged index of 500 stocks that is generally representative of the performance of larger companies in the United States.

The Fund pursues its investment objective by applying a mathematical investment process to construct an investment portfolio from the universe of common stocks within its named benchmark index. The goal of this process is to build a portfolio of stocks in a more efficient combination than the named benchmark index. The process seeks to capitalize on the natural volatility of the market by searching for stocks within the index that have high relative volatility (providing the potential for excess returns) but that essentially move in opposite directions or have low correlation to each other (providing the potential for lower relative risk). By constructing the portfolio in this manner and periodically rebalancing the portfolio to maintain potentially more efficient weightings, INTECH’s mathematical investment process seeks to create a portfolio that, over time, produces returns in excess of its named benchmark index with risks similar to that of the benchmark index. The rebalancing techniques used by INTECH may result in a higher portfolio turnover compared to a “buy and hold” fund strategy.

Risk [Heading]

rr_RiskHeading

PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Investment Process Risk. The proprietary mathematical investment process used by INTECH may not achieve the desired results. On an occasional basis, INTECH considers changes to its mathematical investment process. These changes may result in changes to the portfolio, might not provide the intended results, and may adversely impact the Fund’s performance.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

rr_RiskLoseMoney

The biggest risk is that the Fund’s returns will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

PERFORMANCE INFORMATION

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares, the initial share class) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund commenced operations on July 6, 2009.

•   The performance shown for Class T Shares is calculated using the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers.
•   The performance shown for Class A Shares, Class C Shares, and Class S Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers.
•   The performance shown for Class I Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers.

If Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund had been available during periods prior to July 6, 2009, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, and Class I Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-877-335-2687

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

janus.com/advisor/mutual-funds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns for Class T Shares (calendar year-end)

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Best Quarter:  Second Quarter 2009  14.79%     Worst Quarter:   Fourth Quarter 2008  −21.49%

Year to Date Return, Label

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 14.92%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares, the initial share class). After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

INTECH U.S. Core Fund | Class A, C, S, I, T Shares | Class A

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class A

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class A

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.54%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.20%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.99%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleYear01

670

3 Years

rr_ExpenseExampleYear03

872

5 Years

rr_ExpenseExampleYear05

1,091

10 Years

rr_ExpenseExampleYear10

1,718

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

670

3 Years

rr_ExpenseExampleNoRedemptionYear03

872

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,091

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,718

INTECH U.S. Core Fund | Class A, C, S, I, T Shares | Class C

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class C

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

1.00%

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class C

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.54%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

0.29%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.83%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleYear01

286

3 Years

rr_ExpenseExampleYear03

576

5 Years

rr_ExpenseExampleYear05

990

10 Years

rr_ExpenseExampleYear10

2,148

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

186

3 Years

rr_ExpenseExampleNoRedemptionYear03

576

5 Years

rr_ExpenseExampleNoRedemptionYear05

990

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,148

INTECH U.S. Core Fund | Class A, C, S, I, T Shares | Class S

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class S

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class S

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.54%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.37%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.16%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleYear01

118

3 Years

rr_ExpenseExampleYear03

368

5 Years

rr_ExpenseExampleYear05

638

10 Years

rr_ExpenseExampleYear10

1,409

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

118

3 Years

rr_ExpenseExampleNoRedemptionYear03

368

5 Years

rr_ExpenseExampleNoRedemptionYear05

638

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,409

INTECH U.S. Core Fund | Class A, C, S, I, T Shares | Class I

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class I

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class I

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.54%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.18%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.72%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleYear01

74

3 Years

rr_ExpenseExampleYear03

230

5 Years

rr_ExpenseExampleYear05

401

10 Years

rr_ExpenseExampleYear10

894

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

74

3 Years

rr_ExpenseExampleNoRedemptionYear03

230

5 Years

rr_ExpenseExampleNoRedemptionYear05

401

10 Years

rr_ExpenseExampleNoRedemptionYear10

894

INTECH U.S. Core Fund | Class A, C, S, I, T Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees Column [Text]

rr_ShareholderFeesColumnName

Class T

Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)

rr_MaximumDeferredSalesChargeOverOther

none

Operating Expenses Column [Text]

rr_OperatingExpensesColumnName

Class T

Management Fees (may adjust up or down)

rr_ManagementFeesOverAssets

0.54%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.37%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.91%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleYear01

93

3 Years

rr_ExpenseExampleYear03

290

5 Years

rr_ExpenseExampleYear05

504

10 Years

rr_ExpenseExampleYear10

1,120

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleNoRedemptionByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

93

3 Years

rr_ExpenseExampleNoRedemptionYear03

290

5 Years

rr_ExpenseExampleNoRedemptionYear05

504

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,120

2004

rr_AnnualReturn2004

17.68%

2005

rr_AnnualReturn2005

11.06%

2006

rr_AnnualReturn2006

11.37%

2007

rr_AnnualReturn2007

6.40%

2008

rr_AnnualReturn2008

(36.57%)

2009

rr_AnnualReturn2009

22.91%

2010

rr_AnnualReturn2010

16.28%

2011

rr_AnnualReturn2011

4.97%

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

14.92%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

14.79%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(21.49%)

INTECH U.S. Core Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class A

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class A Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[1]

1 Year

rr_AverageAnnualReturnYear01

(1.16%)

5 Years

rr_AverageAnnualReturnYear05

(1.16%)

Since Inception

rr_AverageAnnualReturnSinceInception

6.78%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 28, 2003

INTECH U.S. Core Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class C

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class C Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

^[2]

1 Year

rr_AverageAnnualReturnYear01

2.99%

5 Years

rr_AverageAnnualReturnYear05

(0.72%)

Since Inception

rr_AverageAnnualReturnSinceInception

6.71%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 28, 2003

INTECH U.S. Core Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class S

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class S Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

4.71%

5 Years

rr_AverageAnnualReturnYear05

(0.14%)

Since Inception

rr_AverageAnnualReturnSinceInception

7.31%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 28, 2003

INTECH U.S. Core Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class I

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class I Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

5.18%

5 Years

rr_AverageAnnualReturnYear05

0.25%

Since Inception

rr_AverageAnnualReturnSinceInception

7.79%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 28, 2003

INTECH U.S. Core Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

4.97%

5 Years

rr_AverageAnnualReturnYear05

0.25%

Since Inception

rr_AverageAnnualReturnSinceInception

7.79%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 28, 2003

INTECH U.S. Core Fund | Class A, C, S, I, T Shares | Return After Taxes on Distributions | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

4.83%

5 Years

rr_AverageAnnualReturnYear05

(0.23%)

Since Inception

rr_AverageAnnualReturnSinceInception

7.07%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 28, 2003

INTECH U.S. Core Fund | Class A, C, S, I, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class T

Risk/Return:

rr_RiskReturnAbstract

Column

rr_AverageAnnualReturnColumnName

Class T Shares

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[3]

1 Year

rr_AverageAnnualReturnYear01

3.42%

5 Years

rr_AverageAnnualReturnYear05

0.18%

Since Inception

rr_AverageAnnualReturnSinceInception

6.72%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 28, 2003

INTECH U.S. Core Fund | Class A, C, S, I, T Shares | S&P 500 Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

S&P 500^® Index

1 Year

rr_AverageAnnualReturnYear01

2.11%

5 Years

rr_AverageAnnualReturnYear05

(0.25%)

Since Inception

rr_AverageAnnualReturnSinceInception

6.77%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 28, 2003

[1] Calculated assuming maximum permitted sales loads.

[2] The one year return is calculated to include the contingent deferred sales charge.

[3] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Perkins Select Value Fund | Class D Shares

Fund summary

Perkins Select Value Fund

INVESTMENT OBJECTIVE

Perkins Select Value Fund seeks capital appreciation.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses		Perkins Select Value Fund Class D Shares Class D
Operating Expenses Column [Text]		Class D
Management Fees (may adjust up or down)		0.70%
Other Expenses		1.04%
Total Annual Fund Operating Expenses	[1]	1.74%
Fee Waiver	[1]	0.55%
Total Annual Fund Operating Expenses After Fee Waiver	[1]	1.19%

EXAMPLE:

The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Perkins Select Value Fund Class D Shares Class D	Class D Shares	177	548	944	2,052

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the period December 15, 2011 to June 30, 2012, the Fund’s portfolio turnover rate was 80% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objective by investing primarily in common stocks selected for their capital appreciation potential. The Fund primarily invests in the common stocks of companies of any size whose stock prices the portfolio managers believe to be undervalued. The Fund may also invest in foreign equity and debt securities, which may include investments in emerging markets. In addition, when the portfolio managers believe that market conditions are unfavorable for investing, or when they are otherwise unable to locate attractive investment opportunities, the Fund’s cash or similar investments may increase.

The Fund focuses on companies that have fallen out of favor with the market or that appear to be temporarily misunderstood by the investment community. The Fund’s portfolio managers generally look for companies with:

• strong balance sheets and solid recurring free cash flows
• attractive relative and absolute valuation ratios or that have underperformed recently
• favorable reward to risk characteristics

The Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices, as substitutes for securities in which the Fund invests. The Fund may invest in derivative instruments (by taking long and/or short positions) for different purposes, including hedging (to offset risks associated with an investment, currency exposure, or market conditions) and to earn income and enhance returns. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the Fund’s portfolio managers. When the Fund’s investments in cash or similar investments increase due to a lack of favorable investment opportunities or other extraordinary factors, the Fund may not participate in market advances or declines to the same extent that it would if the Fund had been fully invested.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The Fund does not have a full calendar year of operations. Performance information for certain periods is included in the Fund’s first annual and/or semiannual report.

[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding any performance adjustments to management fees, administrative services fees payable pursuant to the Transfer Agency Agreement, brokerage commissions, interest, dividends, taxes, acquired fund fees and expenses, and extraordinary expenses) to 1.00% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	JANUS INVESTMENT FUND
Prospectus Date	rr_ProspectusDate	Oct. 26, 2012
Janus Real Return Fund | Class D Shares
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Fund summary Janus Real Return Fund (formerly named Janus Real Return Allocation Fund)
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Janus Real Return Fund seeks real return consistent with preservation of capital.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE FUND
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	November 1, 2013
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover:
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 45% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	45.00%
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE:
Expense Example by Year [Heading]	rr_ExpenseExampleByYearHeading	The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers or recoupments (if applicable) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Fund pursues its investment objective by primarily investing in U.S. Treasury securities, short-duration high-yield/high-risk debt, commodity-linked investments, and equity securities. The Fund’s investments in U.S. Treasury securities may also include Treasury Inflation Protected Securities, also known as TIPS. As utilized by the Fund, each of these types of investments may be considered an “inflation-related investment,” which are those that may provide what is known as “real return,” or a rate of return above the rate of inflation over a full market cycle. Due to the nature of securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds. The Fund may invest up to 90% of its net assets in short-duration high-yield/high-risk debt securities. The Fund’s investments in short-duration high-yield/high-risk securities include debt rated below investment grade, also known as “junk bonds.” Securities rated below investment grade may include their unrated equivalents or other high-yielding securities the portfolio managers believe offer attractive risk/return characteristics. The Fund may also invest in certain investment grade debt instruments, including corporate bonds, government bonds, municipal bonds, mortgage-backed securities, zero-coupon bonds, and agency securities. The Fund may invest in foreign debt securities. To seek exposure to the commodities markets, the Fund may invest in commodity-linked investments such as commodity-related exchange-traded funds (“ETFs”), commodity index-linked swap agreements, commodity options and futures, and options on futures that provide exposure to the investment returns of the commodities markets. The Fund may also invest in other commodity-linked derivative instruments, such as commodity-linked notes (“structured notes”). The Fund’s investments in equity securities may include common stock, preferred stock, and convertible securities, all of which may include exposure to foreign markets. The Fund may invest in companies of any market capitalization. The Fund’s equity investments may also include securities of real estate-related companies, including, but not limited to, real estate investment trusts (“REITs”) and similar REIT-like entities, such as foreign entities that have REIT characteristics. The Fund may also invest in derivative instruments (by taking long and/or short positions) for various purposes, including hedging by shorting interest rate futures against long positions in TIPS, using inflation index swaps to hedge against unexpected changes in the rate of inflation, using interest rate swaps to hedge against changes in interest rates, to increase or decrease the Fund’s exposure to a particular market, to manage or adjust the risk profile of the Fund related to an investment, and to earn income and enhance returns. The Fund’s exposure to derivatives will vary, is not limited to those derivatives listed, and could be significant at times. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission. The Fund may also use reverse repurchase agreements to generate income as part of its inflation-related strategies. Proceeds from reverse repurchase agreement transactions may be invested in other securities or instruments to attempt to increase the Fund’s investment return. The Fund may also invest in money market instruments, buy backs or dollar rolls, other securitized debt products, bank loans, various when-issued securities, exchange-traded notes, and other investment companies. In addition to considering economic factors such as the rate of inflation and the effect of interest rates on the Fund’s investments, the portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.
Risk [Heading]	rr_RiskHeading	PRINCIPAL INVESTMENT RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money. Inflation-Related Investment Risk. Inflation index swaps and other inflation-linked securities are subject to inflation risk. A swap held long by the Fund can potentially lose value if the rate of inflation over the life of the swap is less than the fixed rate that the Fund agrees to pay at the initiation of the swap. Except for the Fund’s investments in U.S. Treasury securities, which are guaranteed as to principal by the U.S. Treasury, the inflation-adjusted principal value of inflation-linked securities repaid at maturity may be less than the original principal. Because of the inflation-linked adjustment feature, inflation-linked securities typically have lower yields than conventional fixed-rate securities. In the event of deflation, where prices decline over time, the principal and income of inflation-linked securities will likely decline, resulting in losses to the Fund. High-Yield/High-Risk Bond Risk. The Fund may invest up to 90% of its net assets in higher-yielding/higher-risk bonds, also known as “junk” bonds. High-yield/high-risk bonds may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value. Commodity-Linked Investments Risk. The Fund may invest in various commodity-linked investments that provide exposure to the commodities markets. Such exposure may subject the Fund to greater volatility than investments in traditional securities. The value of a given commodity-linked derivative investment typically is based upon the price movements of a physical commodity (such as heating oil, livestock, or agricultural products), a commodity futures contract or commodity index, or some other readily measurable economic variable. The value of commodity-linked derivative instruments may therefore be affected by changes in overall market movements, volatility of the underlying benchmark, changes in interest rates, or other factors affecting a particular industry or commodity such as drought, floods, weather, livestock disease, embargoes, tariffs, and international economic, political, and regulatory developments. Exchange-Traded Funds Risk. The Fund may invest in ETFs which are typically open-end investment companies that are traded on a national securities exchange. ETFs typically incur fees, such as investment advisory fees and other operating expenses that are separate from those of the Fund, which will be indirectly paid by the Fund. As a result, the cost of investing in the Fund may be higher than the cost of investing directly in ETFs and may be higher than other mutual funds that invest directly in stocks and bonds. Further, the price movement of an ETF may fluctuate against the underlying securities or commodities it tracks and may result in a loss. Because the value of ETF shares depends on the demand in the market, the Fund may not be able to purchase or sell an ETF at the most optimal time, which could adversely affect the Fund’s performance. The ETFs in which the Fund invests are subject to specific risks, depending on the investment strategy of the ETF. In turn, the Fund will be subject to substantially the same risks as those associated with direct exposure to the securities or commodities held by the ETF. Because the Fund may invest in a broad range of ETFs, such risks may include, but are not limited to, leverage risk, foreign exposure risk, and commodities risk. Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth. Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities. Sovereign Debt Risk. The Fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However, investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner. Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited. Counterparty Risk. Certain derivative and “over-the-counter” instruments, such as swaps and forwards, are subject to the risk that the other party to a contract will not fulfill its contractual obligations. Leverage Risk. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. In particular, certain commodity-linked investments may subject the Fund to leveraged market exposure to commodities. Leverage also occurs when the Fund increases its assets available for investment through borrowings, reverse repurchase agreements, or similar transactions. The Fund’s use of leverage can magnify the effect of any gains or losses, causing the Fund to be more volatile than if it had not been leveraged. There is no assurance that any leveraging strategy will be successful. Reverse Repurchase Agreement Risk. Reverse repurchase agreements involve leverage risk, counterparty risk, and the risk that the value of securities that the Fund is obligated to repurchase under the agreement may decline below the repurchase price. When the Fund invests reverse repurchase transaction proceeds, the Fund is at risk for any fluctuations in the value of securities in which the proceeds are invested. To the extent the Fund uses reverse repurchase agreements, the value of an investment in the Fund may be more volatile, and such transactions may increase the Fund’s overall investment exposure. Additionally, interest expenses related to reverse repurchase transactions could exceed the rate of return on debt obligations and other investments held by the Fund, thereby reducing returns to shareholders. Foreign Exposure Risk. The Fund normally has significant exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries. Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money. Growth Securities Risk. The Fund invests in companies after assessing their growth potential. Securities of companies perceived to be “growth” companies may be more volatile than other stocks and may involve special risks. If the portfolio managers’ perception of a company’s growth potential is not realized, the securities purchased may not perform as expected, reducing the Fund’s returns. In addition, because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “growth” stocks may perform differently from the market as a whole and other types of securities. Real Estate Risk. An investment in the Fund may be subject to many of the same risks as a direct investment in real estate. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets. Nondiversification Risk. The Fund is classified as nondiversified under the Investment Company Act of 1940, as amended. This gives the Fund’s portfolio managers more flexibility to hold larger positions in a smaller number of securities. As a result, an increase or decrease in the value of a single security held by the Fund may have a greater impact on the Fund’s net asset value and total return. Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Risk Lose Money [Text]	rr_RiskLoseMoney	Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.
Risk Nondiversified Status [Text]	rr_RiskNondiversifiedStatus	Nondiversification Risk. The Fund is classified as nondiversified under the Investment Company Act of 1940, as amended. This gives the Fund’s portfolio managers more flexibility to hold larger positions in a smaller number of securities. As a result, an increase or decrease in the value of a single security held by the Fund may have a greater impact on the Fund’s net asset value and total return.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	PERFORMANCE INFORMATION
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The Fund does not have a full calendar year of operations. Performance information for certain periods is included in the Fund’s first annual and/or semiannual report.
Performance One Year or Less [Text]	rr_PerformanceOneYearOrLess	The Fund does not have a full calendar year of operations.
Janus Real Return Fund | Class D Shares | Class D
Risk/Return:	rr_RiskReturnAbstract
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class D
Management Fees	rr_ManagementFeesOverAssets	0.55%
Other Expenses	rr_OtherExpensesOverAssets	0.97%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.52%	[2]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	0.64%	[2]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	0.88%	[2]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class D Shares
1 Year	rr_ExpenseExampleYear01	154
3 Years	rr_ExpenseExampleYear03	479
5 Years	rr_ExpenseExampleYear05	827
10 Years	rr_ExpenseExampleYear10	1,808

[1] Other Expenses are based on the estimated expenses that the Fund expects to incur.

[2] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding administrative services fees payable pursuant to the Transfer Agency Agreement, brokerage commissions, interest, dividends, taxes, acquired fund fees and expenses, and extraordinary expenses) to 0.76% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees. For a period of three years subsequent to the Fund's commencement of operations (May 13, 2011) or until the Fund's assets exceed the first breakpoint in the investment advisory fee schedule, whichever occurs first, Janus Capital may recover from the Fund fees and expenses previously waived or reimbursed, which could then be considered a deferral, if the Fund's expense ratio, including recovered expenses, falls below the expense limit.

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Janus Government Money Market Fund | Class T Shares

Fund summary

Janus Government Money Market Fund

INVESTMENT OBJECTIVES

Janus Government Money Market Fund seeks capital preservation and liquidity

with current income as a secondary objective.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses

Janus Government Money Market Fund

Class T Shares

Class T

Operating Expenses Column [Text]

Class T

Management Fees

0.20%

Other Expenses

0.51%

Total Annual Fund Operating Expenses

0.71%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)

Expense Example, By Year, Column [Text]

1 Year

3 Years

5 Years

10 Years

Janus Government Money Market Fund Class T Shares Class T

Class T Shares

73

227

395

883

PRINCIPAL INVESTMENT STRATEGIES

The Fund pursues its investment objectives by investing exclusively in obligations issued and/or guaranteed as to principal and interest by the United States Government or by its agencies and instrumentalities, and repurchase agreements secured by such obligations. Although U.S. Government agencies and instrumentalities may be chartered or sponsored by Acts of Congress, their securities are not issued by, and may not be guaranteed by (i.e., backed by the full faith and credit of), the United States Treasury. Some government agency and instrumentality securities not backed by the full faith and credit of the United States are supported by the issuer’s ability to borrow from the U.S. Treasury, some are supported only by the credit of the issuer, and some are supported by the United States in some other way. For securities not backed by the full faith and credit of the U.S. Treasury, the Fund must look principally to the agency or instrumentality issuing or guaranteeing the securities for repayment and may not be able to assert a claim against the United States if the agency or instrumentality does not meet its commitment. The Fund’s investments in securities issued by U.S. Government agencies and instrumentalities may be significant.

The Fund will:

• invest in high quality, short-term money market instruments that present minimal credit risks, as determined by Janus Capital

• invest only in U.S. dollar-denominated instruments that have a remaining maturity of 397 days or less (as calculated pursuant to Rule 2a-7 under the Investment Company Act of 1940, as amended)

• maintain a dollar-weighted average portfolio maturity of 60 days or less and maintain a dollar-weighted average portfolio life (portfolio maturity measured without reference to any maturity shortening provisions of adjustable rate securities by reference to their interest rate reset dates) of 120 days or less

PRINCIPAL INVESTMENT RISKS

Market Risk. The Fund’s yield will vary as the short-term securities in its portfolio mature and the proceeds are reinvested in securities with different interest rates. For capital preservation and liquidity, the Fund may have a greater concentration in short-term securities including, but not limited to, investing up to all of its assets in overnight securities, which may result in a reduction of the Fund’s yield. Over time, the real value of the Fund’s yield may be eroded by inflation. Although the Fund invests only in high-quality, short-term money market instruments, there is a risk that the value of the securities it holds will fall as a result of changes in interest rates, an issuer’s actual or perceived creditworthiness, or an issuer’s ability to meet its obligations. The credit quality of the Fund’s holdings can change rapidly in certain market environments and any downgrade or default of a portfolio security could cause the Fund’s share price or yield to fall.

Collateral Risk. With respect to collateral received in repurchase transactions or other investments, the Fund may have significant exposure to government agencies not secured by the full faith and credit of the United States. Such exposure, depending on market conditions, could have a negative impact on the Fund, including minimizing the value of any collateral.

Money Market Risk. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares, the initial share class) of the Fund commenced operations with the Fund’s inception. The performance shown for Class T Shares is calculated using the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table shows how the Fund’s returns over different periods average out. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Annual Total Returns for Class T Shares (calendar year-end)

Best Quarter:  Fourth Quarter 2006  1.21%          Worst Quarter:  Third Quarter 2011  0.00%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 0.00%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns

Column

Label

1 Year

5 Years

10 Years

Since Inception

Inception Date

Janus Government Money Market Fund Class T Shares Class T Return Before Taxes

Class T Shares

Return Before Taxes

none

1.29%

1.64%

2.99%

Feb. 14, 1995

The 7-day yield on December 31, 2011 was 0.00% for Janus Government Money Market Fund.

XML

Janus Growth Allocation Fund | Class D Shares

Fund summary

Janus Growth Allocation Fund

INVESTMENT OBJECTIVE

Janus Growth Allocation Fund seeks total return through a primary emphasis on growth of capital with a secondary emphasis on income.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses		Janus Growth Allocation Fund Class D Shares Class D
Operating Expenses Column [Text]		Class D
Management Fees		0.05%
Other Expenses	[1]	0.26%
Acquired Fund Fees and Expenses		0.76%
Total Annual Fund Operating Expenses		1.07%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses (including the operating expenses of the underlying funds) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example (USD $)	Expense Example, By Year, Column [Text]	1 Year	3 Years	5 Years	10 Years
Janus Growth Allocation Fund Class D Shares Class D	Class D Shares	109	340	590	1,306

Portfolio Turnover:

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 18% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES

The Fund seeks to achieve its investment objective by investing in other Janus mutual funds (“underlying funds”) that represent a variety of asset classes and investment styles. The Fund pursues this objective by investing in a diversified portfolio of underlying funds resulting in an allocation of the Fund’s investments that normally provides exposure of approximately 80% to stocks and 20% to bonds and money market securities. The target allocation and the allocation of the Fund’s assets among underlying funds are based on quantitative and qualitative analysis. Because it invests in other funds, the Fund is considered a “fund of funds.”

The Fund’s asset allocation is intended to diversify investments among stocks, bonds, and cash equivalents. The portfolio manager regularly reviews the allocation of Fund assets in the underlying funds and may modify the underlying funds’ weightings or substitute other underlying funds to emphasize and mitigate risk exposures that may arise as a result of the implementation of the allocations. An independent asset allocation service provides evaluations of asset allocations that the portfolio manager may use in implementing the allocations among the underlying funds. The portfolio manager continually monitors asset class allocations and periodically rebalances the Fund’s investments in the underlying funds. The portfolio manager may change the Fund’s asset class allocations, the underlying funds, an underlying fund’s asset category, or weightings among asset classes or underlying funds without prior shareholder notice.

The Fund will normally allocate approximately 80% of its investments to underlying funds that provide varying exposure to common stocks of large U.S.-based companies, small- to mid-capitalization companies, and international companies (including those with exposure to emerging markets); and approximately 20% of its investments to underlying bond funds and money market instruments. Refer to Appendix A in this Prospectus for a brief description of the investment strategies of each of the currently available underlying funds.

When market conditions dictate a more defensive strategy, the Fund or an underlying fund may temporarily hold cash or invest its assets in temporary investments. In that case, the Fund may take positions that are inconsistent with its investment objective. As a result, the Fund may not achieve its investment objective.

PRINCIPAL INVESTMENT RISKS

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking growth of capital and, to a lesser extent, income. Investments in a portfolio with common stock exposure tend to be more volatile than many other investment choices.

Main Risks Associated with the Fund
Allocation Risk. The Fund’s ability to achieve its investment objective depends largely upon the portfolio manager’s allocation of assets among the underlying funds and other securities, using the optimization process (a process that utilizes quantitative analysis of a number of factors, such as historical risk, performance, fund classifications, and the relationship among underlying funds) and the judgment of the portfolio manager. You could lose money on your investment in the Fund as a result of these allocations. The Fund will typically invest in a number of different underlying funds; however, to the extent that the Fund invests a significant portion of its assets in a single underlying fund, it will be more sensitive to the risks associated with that fund and any investments in which that fund concentrates.

Affiliated Fund Risk. Janus Capital has the authority to select and substitute underlying affiliated mutual funds. The fees paid to Janus Capital by some Janus mutual funds are generally higher than the fees paid to Janus Capital by the Fund or by other funds and share classes available for investment by the Fund. These conditions may create a conflict of interest when selecting underlying affiliated mutual funds and share classes for investment. Janus Capital, however, is a fiduciary to the Fund and its shareholders and is legally obligated to act in their best interest when selecting underlying affiliated mutual funds.

Main Risks Associated with the Underlying Funds and Securities
The biggest risk is that the underlying funds’ returns will vary, and you could lose money.

Market Risk. Approximately 80% of the Fund’s assets are allocated to equity investments through investments in underlying funds. The value of an underlying fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if a portfolio manager’s belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of an underlying fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money.

Fixed-Income Securities Risk. Approximately 20% of the Fund’s assets are allocated to fixed-income securities through investments in underlying funds. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause an underlying fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which an underlying fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that an underlying fund’s portfolio manager would like or at the price that the portfolio manager believes the security is currently worth.

Foreign Exposure Risk. Certain underlying funds may have significant exposure to foreign markets as a result of their investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, an underlying fund’s returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. A market swing in one or more countries or regions where an underlying fund has invested a significant amount of its assets may have a greater effect on an underlying fund’s performance than it would in a more geographically diversified portfolio. An underlying fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Emerging Markets Risk. The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities involve a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. In addition, an underlying fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of an underlying fund’s investments. To the extent that an underlying fund invests a significant portion of its assets in the securities of issuers in or companies of a single country or region, it is more likely to be impacted by events or conditions affecting that country or region, which could have a negative impact on the Fund’s performance. Some of the risks of investing directly in foreign and emerging market securities may be reduced when an underlying fund invests indirectly in foreign securities through various other investment vehicles including derivatives, which also involve other risks.

Sovereign Debt Risk. An underlying fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Exchange-Traded Funds Risk. Certain underlying funds may purchase shares of exchange-traded funds (“ETFs”) to gain exposure to a particular portion of the market. ETFs are pooled investment vehicles, which may be managed or unmanaged, that generally seek to track the performance of a specific index. ETFs are traded on an exchange at market prices that may vary from the net asset value of their underlying investments. When an underlying fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF’s expenses. ETFs have certain inherent risks generally associated with investments in a portfolio of securities in which the ETF is invested, including the risk that the general level of stock prices may decline, thereby adversely affecting the value of each unit of the ETF. ETFs also involve the risk that an active trading market for an ETF’s shares may not develop or be maintained.

Exchange-Traded Notes Risk. Certain underlying funds may invest in exchange-traded notes (“ETNs”), which are debt securities whose returns are linked to a particular index. ETNs are typically linked to the performance of a commodities index that reflects the potential return on unleveraged investments in futures contracts of physical commodities, plus a specified rate of interest that could be earned on cash collateral. ETNs are subject to credit risk. The value of an ETN may vary and may be influenced by time to maturity, level of supply and demand for the ETN, volatility and lack of liquidity in underlying commodities markets, changes in the applicable interest rates, changes in the issuer’s credit rating, and economic, legal, political, or geographic events that affect the referenced commodity. When an underlying fund invests in ETNs it will bear its proportionate share of any fees and expenses borne by the ETN. There may be restrictions on an underlying fund’s right to redeem its investment in an ETN, which is meant to be held until maturity. An underlying fund’s decision to sell its ETN holdings may be limited by the availability of a secondary market.

Derivatives Risk. Certain underlying funds may invest in derivatives. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

PERFORMANCE INFORMATION

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares, the predecessor share class. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses in effect during the periods shown, net of any applicable fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. Performance information for each underlying fund is available in its prospectus and/or the most recent annual or semiannual report. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Annual Total Returns for Class D Shares (calendar year-end)

Best Quarter:  Second Quarter 2009  18.37%        Worst Quarter:  Fourth Quarter 2008  −18.05%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 11.53%.

Average Annual Total Returns (periods ended 12/31/11)

Average Annual Total Returns Janus Growth Allocation Fund Class D Shares	Column	Label		1 Year	5 Years	Since Inception	Inception Date
Class D Return Before Taxes	Class D Shares	Return Before Taxes		(6.44%)	1.67%	4.30%	Dec. 30, 2005
Class D Return After Taxes on Distributions	Class D Shares	Return After Taxes on Distributions		(6.87%)	1.03%	3.68%	Dec. 30, 2005
Class D Return After Taxes on Distributions and Sale of Fund Shares	Class D Shares	Return After Taxes on Distributions and Sale of Fund Shares	[1]	(4.03%)	1.16%	3.44%	Dec. 30, 2005
S&P 500 Index (reflects no deduction for expenses, fees, or taxes)		S&P 500® Index		2.11%	(0.25%)	2.26%	Dec. 30, 2005
Growth Allocation Index (reflects no deduction for expenses, fees, or taxes)		Growth Allocation Index		(2.07%)	0.80%	3.31%	Dec. 30, 2005

The Growth Allocation Index is an internally-calculated, hypothetical combination of unmanaged indices that combines total returns from the Dow Jones Wilshire 5000 Index (50%), the MSCI EAFE^® Index (25%), the Barclays U.S. Aggregate Bond Index (20%), and the Morgan Stanley Capital International Emerging Markets Free Index^sm (5%).

After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; and for the Fund’s Class J Shares, the predecessor share class, for the periods prior to February 16, 2010. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

[1] Other Expenses are based on the estimated expenses that the Fund expects to incur.

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 26, 2012

Janus High-Yield Fund | Class D Shares

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund summary

Janus High-Yield Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVES

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Janus High-Yield Fund seeks to obtain high current income.

Objective, Secondary [Text Block]

rr_ObjectiveSecondaryTextBlock

Capital appreciation is a secondary investment objective when consistent with its primary investment objective.

Expense [Heading]

rr_ExpenseHeading

FEES AND EXPENSES OF THE FUND

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover:

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 61% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

61.00%

Expense Example [Heading]

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EXAMPLE:

Expense Example by Year [Heading]

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The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example Narrative [Text Block]

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The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

Strategy [Heading]

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PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

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The Fund pursues its investment objectives by investing, under normal circumstances, at least 80% of its net assets in high-yield/high-risk securities rated below investment grade. Securities rated below investment grade may include their unrated equivalents or other high-yielding securities the portfolio managers believe offer attractive risk/return characteristics. The Fund may at times invest all of its assets in such securities. The Fund may also invest in bank loans, money market instruments, and foreign debt securities (which may include investments in emerging markets). Due to the nature of securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

In addition, the Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. In particular, the Fund may use interest rate futures to manage portfolio risk. The Fund’s exposure to derivatives will vary. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

In addition to considering economic factors such as the effect of interest rates on the Fund’s investments, the portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income-producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

Risk [Heading]

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PRINCIPAL INVESTMENT RISKS

Risk Narrative [Text Block]

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Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which the Fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the Fund would like or at the price that the portfolio managers believe the security is currently worth.

High-Yield/High-Risk Bond Risk. The Fund may invest without limit in higher-yielding/higher-risk bonds, also known as “junk” bonds. High-yield/high-risk bonds may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Bank Loan Risk. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. Participation interests and assignments involve credit, interest rate, and liquidity risk. In addition, the bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. To the extent the Fund invests in foreign debt securities, such investments are sensitive to changes in interest rates. Additionally, investments in securities of foreign governments involve the risk that a foreign government may not be willing or able to pay interest or repay principal when due. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

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Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Risk Not Insured Depository Institution [Text]

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An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

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PERFORMANCE INFORMATION

Performance Narrative [Text Block]

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The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares, the predecessor share class. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses in effect during the periods shown, net of any applicable fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Performance Information Illustrates Variability of Returns [Text]

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The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

Performance Additional Market Index [Text]

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The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.

Performance Availability Phone [Text]

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1-800-525-3713

Performance Availability Website Address [Text]

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janus.com/allfunds

Performance Past Does Not Indicate Future [Text]

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The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart [Heading]

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Annual Total Returns for Class D Shares (calendar year-end)

Bar Chart Closing [Text Block]

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Best Quarter:  Second Quarter 2009  14.93%          Worst Quarter:  Fourth Quarter 2008  −12.96%

Year to Date Return, Label

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The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 10.80%.

Performance Table Heading

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Average Annual Total Returns (periods ended 12/31/11)

Performance Table Uses Highest Federal Rate

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After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

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Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Explanation after Tax Higher

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If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Performance Table Narrative

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After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; and for the Fund’s Class J Shares, the predecessor share class, for the periods prior to February 16, 2010. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Performance Table Closing [Text Block]

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Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Janus High-Yield Fund | Class D Shares | Class D

Risk/Return:

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Operating Expenses Column [Text]

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Class D

Management Fees

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0.57%

Other Expenses

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0.19%

Total Annual Fund Operating Expenses

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0.76%

Expense Example, By Year, Column [Text]

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Class D Shares

1 Year

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78

3 Years

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243

5 Years

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422

10 Years

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942

2002

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2.56%

2003

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16.04%

2004

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9.42%

2005

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2.77%

2006

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11.10%

2007

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1.35%

2008

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(19.32%)

2009

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40.86%

2010

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15.80%

2011

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3.32%

Bar Chart, Year to Date Return, Date

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Sep. 30, 2012

Bar Chart, Year to Date Return

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10.80%

Highest Quarterly Return, Label

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Best Quarter:

Highest Quarterly Return, Date

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Jun. 30, 2009

Highest Quarterly Return

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14.93%

Lowest Quarterly Return, Label

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Worst Quarter:

Lowest Quarterly Return, Date

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Dec. 31, 2008

Lowest Quarterly Return

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(12.96%)

Janus High-Yield Fund | Class D Shares | Return Before Taxes | Class D

Risk/Return:

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Column

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Class D Shares

Label

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Return Before Taxes

1 Year

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3.32%

5 Years

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6.62%

10 Years

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7.44%

Since Inception

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7.85%

Inception Date

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Dec. 29, 1995

Janus High-Yield Fund | Class D Shares | Return After Taxes on Distributions | Class D

Risk/Return:

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Column

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Class D Shares

Label

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Return After Taxes on Distributions

1 Year

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0.72%

5 Years

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3.40%

10 Years

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4.49%

Since Inception

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4.55%

Inception Date

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Dec. 29, 1995

Janus High-Yield Fund | Class D Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class D

Risk/Return:

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Column

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Class D Shares

Label

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Return After Taxes on Distributions and Sale of Fund Shares

^[1]

1 Year

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2.15%

5 Years

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3.68%

10 Years

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4.58%

Since Inception

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4.66%

Inception Date

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Dec. 29, 1995

Janus High-Yield Fund | Class D Shares | Barclays U.S. Corporate High-Yield Bond Index (reflects no deduction for expenses, fees, or taxes)

Risk/Return:

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Label

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Barclays U.S. Corporate High-Yield Bond Index

1 Year

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4.98%

5 Years

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7.54%

10 Years

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8.85%

Since Inception

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7.18%

Inception Date

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Dec. 29, 1995

[1] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.