Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Jan. 28, 2015

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

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

FUND SUMMARY

Janus Forty Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Janus Forty 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 51% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

51.00%

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 92 of the Fund’s Prospectus and in the “Purchases” section on page 82 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 normally investing primarily in a core group of 20-40 common stocks selected for their growth potential. The Fund may invest in companies of any size, from larger, well-established companies to smaller, emerging growth companies. The Fund may also invest in foreign securities, which may include investments in emerging markets.

The portfolio manager applies a “bottom up” approach in choosing investments. In other words, the portfolio manager looks at companies one at a time to determine if a company is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.

The Fund may lend portfolio securities on a short-term or long-term basis, in an amount equal to up to one-third of its total assets as determined at the time of the loan origination.

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 or if the 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 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. Market risk may affect a single issuer, industry, economic sector, or the market as a whole.

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 manager’s 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.

Nondiversification Risk. The Fund is classified as nondiversified under the Investment Company Act of 1940, as amended. This gives the Fund’s portfolio manager 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.

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.

Securities Lending Risk. The Fund may seek to earn additional income through lending its securities to certain qualified broker-dealers and institutions. There is the risk that when portfolio securities are lent, the securities may not be returned on a timely basis, and the Fund may experience delays and costs in recovering the security or gaining access to the collateral provided to the Fund to collateralize the loan. If the Fund is unable to recover a security on loan, the Fund may use the collateral to purchase replacement securities in the market. There is a risk that the value of the collateral could decrease below the cost of the replacement security by the time the replacement investment is made, resulting in a loss to the Fund.

Management Risk. The Fund is an actively managed investment portfolio and is therefore subject to the risk that the investment strategies employed for the Fund may fail to produce the intended results. The Fund may underperform its benchmark index or other mutual funds with similar investment objectives.

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 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 manager 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 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, Class I Shares, and Class R Shares of the Fund commenced operations on July 6, 2009, after the reorganization of each corresponding class of shares of Janus Adviser Forty 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 S Shares reflects the performance of the JAD predecessor fund’s Class S Shares (formerly named Class I Shares) from August 1, 2000 to July 6, 2009 (prior to the reorganization), 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. For the periods prior to August 1, 2000, the performance shown for Class S Shares reflects the historical performance of the Retirement Shares of Janus Aspen Series – Forty Portfolio (as a result of a separate prior reorganization of those Retirement Shares into the JAD predecessor fund). The performance shown for certain periods prior to August 1, 2000 was calculated using the fees and expenses of Class S Shares of the JAD predecessor fund, without the effect of any 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. For the periods August 1, 2000 to September 30, 2004, the performance shown for Class A Shares reflects the historical performance of the JAD predecessor fund’s Class S Shares (formerly named Class I Shares). For the periods prior to August 1, 2000, the performance shown for Class A Shares reflects the historical performance of the Retirement Shares of Janus Aspen Series – Forty Portfolio (as a result of a separate prior reorganization of those Retirement Shares into the JAD predecessor fund). The performance shown for certain periods prior to September 30, 2004 was calculated using the fees and expenses of Class S Shares of the JAD predecessor fund, without the effect of any fee and expense limitations or waivers.
• The performance shown for Class C Shares reflects the performance of the JAD predecessor fund’s Class C Shares from September 30, 2002 to July 6, 2009 (prior to the reorganization), calculated using the fees and expenses of Class C Shares of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers. For the periods August 1, 2000 to September 30, 2002, the performance shown for Class C Shares reflects the historical performance of the JAD predecessor fund’s Class S Shares (formerly named Class I Shares). For the periods prior to August 1, 2000, the performance shown for Class C Shares reflects the historical performance of the Retirement Shares of Janus Aspen Series – Forty Portfolio (as a result of a separate prior reorganization of those Retirement Shares into the JAD predecessor fund). The performance shown for certain periods prior to September 30, 2002 was calculated using the fees and expenses of Class S Shares of the JAD predecessor fund, without the effect of any 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. For the periods August 1, 2000 to November 28, 2005, the performance shown for Class I Shares reflects the historical performance of the JAD predecessor fund’s Class S Shares (formerly named Class I Shares). For the periods prior to August 1, 2000, the performance shown for Class I Shares reflects the historical performance of the Retirement Shares of Janus Aspen Series – Forty Portfolio (as a result of a separate prior reorganization of those Retirement Shares into the JAD predecessor fund). The performance shown for certain periods prior to November 28, 2005 was calculated using the fees and expenses of Class S Shares of the JAD predecessor fund, without the effect of any fee and expense limitations or waivers.
• The performance shown for Class N Shares reflects the performance of the Fund’s Class S Shares from July 6, 2009 to May 31, 2012, calculated using the fees and expenses of Class S Shares, net of any applicable fee and expense limitations or waivers. For the period from August 1, 2000 to July 6, 2009, the performance shown for Class N Shares reflects the performance of Class S Shares (formerly named Class I Shares) of the JAD predecessor fund (prior to the reorganization of those Class S Shares into the Fund), 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. For the periods prior to August 1, 2000, the performance shown for Class N Shares reflects the historical performance of the Retirement Shares of Janus Aspen Series – Forty Portfolio (as a result of a separate prior reorganization of those Retirement Shares into the JAD predecessor fund). The performance for certain periods prior to August 1, 2000 was calculated using the fees and expenses of Class S Shares of the JAD predecessor fund, without the effect of any fee and expense limitations or waivers.
• The performance shown for Class R Shares reflects the performance of the JAD predecessor fund’s Class R Shares from September 30, 2004 to July 6, 2009 (prior to the reorganization), calculated using the fees and expenses of Class R Shares of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers. For the periods August 1, 2000 to September 30, 2004, the performance shown for Class R Shares reflects the historical performance of the JAD predecessor fund’s Class S Shares (formerly named Class I Shares). For the periods prior to August 1, 2000, the performance shown for Class R Shares reflects the historical performance of the Retirement Shares of Janus Aspen Series – Forty Portfolio (as a result of a separate prior reorganization of those Retirement Shares into the JAD predecessor fund). The performance shown for certain periods prior to September 30, 2004 was calculated using the fees and expenses of Class R Shares of the JAD predecessor fund, without the effect of any fee and expense limitations or waivers.
• The performance shown for Class T Shares reflects the performance of the JAD predecessor fund’s Class S Shares (formerly named Class I Shares) from August 1, 2000 to July 6, 2009 (prior to the reorganization), 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. For the periods prior to August 1, 2000, the performance shown for Class T Shares reflects the historical performance of the Retirement Shares of Janus Aspen Series – Forty Portfolio (as a result of a separate prior reorganization of those Retirement Shares into the JAD predecessor fund). The performance shown for certain periods prior to August 1, 2000 was calculated using the fees and expenses of Class S Shares of the JAD predecessor fund, without the effect of any fee and expense limitations or waivers.

If Class A Shares, Class C Shares, Class I Shares, Class R Shares, and Class T Shares of the Fund had been available during each period prior to July 6, 2009, or Class N Shares of the Fund had been available during periods prior to May 31, 2012, 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, Class N Shares, Class R 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 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 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:  2nd Quarter 2009  20.90%          Worst Quarter:  4th Quarter 2008  −25.11%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/14)

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

The Russell 1000^® Growth Index measures the performance of those Russell 1000^® companies with higher price-to-book ratios and higher forecasted growth values. This index is used to calculate the performance fee adjustment.

The S&P 500^® Index is a commonly recognized, market-capitalization weighted index of 500 widely held equity securities, designed to measure broad U.S. equity performance.

After-tax returns are calculated using distributions for the Fund’s Class S Shares for periods following July 6, 2009; for the JAD predecessor fund’s Class S Shares (formerly named Class I Shares) for the periods August 1, 2000 to July 6, 2009; and actual distributions for other classes of shares for periods prior to August 1, 2000. 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.

Janus Forty 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

0.48%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.19%

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

Janus Forty 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

0.48%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

0.19%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.67%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleYear01

270

3 Years

rr_ExpenseExampleYear03

526

5 Years

rr_ExpenseExampleYear05

907

10 Years

rr_ExpenseExampleYear10

1,976

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

rr_ExpenseExampleNoRedemptionByYearColumnName

Class C Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

170

3 Years

rr_ExpenseExampleNoRedemptionYear03

526

5 Years

rr_ExpenseExampleNoRedemptionYear05

907

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,976

Janus Forty 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

0.48%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.29%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.02%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class S 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 S Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

104

3 Years

rr_ExpenseExampleNoRedemptionYear03

325

5 Years

rr_ExpenseExampleNoRedemptionYear05

563

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,248

2005

rr_AnnualReturn2005

14.60%

2006

rr_AnnualReturn2006

10.18%

2007

rr_AnnualReturn2007

35.57%

2008

rr_AnnualReturn2008

(44.02%)

2009

rr_AnnualReturn2009

43.53%

2010

rr_AnnualReturn2010

5.62%

2011

rr_AnnualReturn2011

(7.32%)

2012

rr_AnnualReturn2012

23.65%

2013

rr_AnnualReturn2013

31.73%

2014

rr_AnnualReturn2014

8.57%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

20.90%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(25.11%)

Janus Forty 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

0.48%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.12%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.60%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class I 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 I Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

61

3 Years

rr_ExpenseExampleNoRedemptionYear03

192

5 Years

rr_ExpenseExampleNoRedemptionYear05

335

10 Years

rr_ExpenseExampleNoRedemptionYear10

750

Janus Forty 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

0.48%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.04%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.52%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class N Shares

1 Year

rr_ExpenseExampleYear01

53

3 Years

rr_ExpenseExampleYear03

167

5 Years

rr_ExpenseExampleYear05

291

10 Years

rr_ExpenseExampleYear10

653

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

rr_ExpenseExampleNoRedemptionByYearColumnName

Class N Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

53

3 Years

rr_ExpenseExampleNoRedemptionYear03

167

5 Years

rr_ExpenseExampleNoRedemptionYear05

291

10 Years

rr_ExpenseExampleNoRedemptionYear10

653

Janus Forty 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

0.48%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.50%

Other Expenses

rr_OtherExpensesOverAssets

0.29%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.27%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class R 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 R Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

129

3 Years

rr_ExpenseExampleNoRedemptionYear03

403

5 Years

rr_ExpenseExampleNoRedemptionYear05

697

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,534

Janus Forty 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

0.48%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.29%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.77%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class T 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 T Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

79

3 Years

rr_ExpenseExampleNoRedemptionYear03

246

5 Years

rr_ExpenseExampleNoRedemptionYear05

428

10 Years

rr_ExpenseExampleNoRedemptionYear10

954

Janus Forty 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

^[1]

1 Year

rr_AverageAnnualReturnYear01

2.28%

5 Years

rr_AverageAnnualReturnYear05

10.39%

10 Years

rr_AverageAnnualReturnYear10

8.60%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

10.47%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 01, 1997

Janus Forty 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

^[2]

1 Year

rr_AverageAnnualReturnYear01

6.93%

5 Years

rr_AverageAnnualReturnYear05

10.83%

10 Years

rr_AverageAnnualReturnYear10

8.41%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

10.13%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 01, 1997

Janus Forty 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

8.57%

5 Years

rr_AverageAnnualReturnYear05

11.60%

10 Years

rr_AverageAnnualReturnYear10

9.06%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

10.72%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 01, 1997

Janus Forty 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

8.88%

5 Years

rr_AverageAnnualReturnYear05

12.02%

10 Years

rr_AverageAnnualReturnYear10

9.06%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

10.72%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 01, 1997

Janus Forty 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

9.07%

5 Years

rr_AverageAnnualReturnYear05

11.60%

10 Years

rr_AverageAnnualReturnYear10

9.06%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

10.72%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 01, 1997

Janus Forty 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

8.18%

5 Years

rr_AverageAnnualReturnYear05

11.27%

10 Years

rr_AverageAnnualReturnYear10

8.77%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

10.47%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 01, 1997

Janus Forty 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

8.81%

5 Years

rr_AverageAnnualReturnYear05

11.85%

10 Years

rr_AverageAnnualReturnYear10

9.06%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

10.72%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 01, 1997

Janus Forty Fund | Class A, C, S, I, N, R, 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

(0.23%)

5 Years

rr_AverageAnnualReturnYear05

8.70%

10 Years

rr_AverageAnnualReturnYear10

7.49%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

9.79%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 01, 1997

Janus Forty Fund | Class A, C, S, I, N, R, 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

11.38%

5 Years

rr_AverageAnnualReturnYear05

9.08%

10 Years

rr_AverageAnnualReturnYear10

7.32%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

9.24%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 01, 1997

Janus Forty Fund | Class A, C, S, I, N, R, 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

13.05%

5 Years

rr_AverageAnnualReturnYear05

15.81%

10 Years

rr_AverageAnnualReturnYear10

8.49%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

6.66%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 01, 1997

Janus Forty Fund | Class A, C, S, I, N, R, 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

13.69%

5 Years

rr_AverageAnnualReturnYear05

15.45%

10 Years

rr_AverageAnnualReturnYear10

7.67%

Since Inception of Predecessor Fund

rr_AverageAnnualReturnSinceInception

7.47%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 01, 1997

[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.