Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Jan. 28, 2015

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

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

FUND SUMMARY

Janus Research Fund

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

Janus Research 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 44% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

44.00%

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 investing primarily in 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.

Janus Capital’s equity research analysts, overseen by the Portfolio Oversight Team led by Janus Capital’s Director of Research Carmel Wellso (the “Research Team”), select investments for the Fund that represent the Research Team’s high-conviction investment ideas in all market capitalizations and styles. The Research Team, comprised of sector specialists, conducts fundamental analysis with a focus on “bottom up” research, quantitative modeling, and valuation analysis. Using this research process, analysts rate their stocks based upon attractiveness. Analysts bring their high-conviction ideas to their respective sector teams. Sector teams compare the appreciation and risk potential of each of the team’s high-conviction ideas and construct a sector portfolio that is intended to maximize the best risk-reward opportunities. Although the Research Team may find high-conviction investment ideas anywhere in the world, the Research Team emphasizes investments in securities of U.S.-based issuers.

Positions may be sold when, among other things, there is no longer high conviction in the return potential of the investment or if the risk characteristics have caused a re-evaluation of the opportunity. This may occur if the stock has appreciated and reflects the anticipated value, if another company represents a better risk-reward opportunity, or if the investment’s fundamental characteristics deteriorate. Securities may also be sold from the portfolio to rebalance sector weightings.

Ms. Wellso oversees the investment process and is responsible for the day-to-day management of the Fund. It is expected that the Fund will be broadly diversified among a variety of industry sectors. The Fund intends to be fully invested under normal circumstances. However, under unusual circumstances, if the Research Team does not have high conviction in enough investment opportunities, the Fund’s uninvested assets may be held in cash or similar instruments.

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 investment personnel’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 investment personnel’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. The Fund’s Research Team compares and broadly matches the Fund’s sector weights to those of a growth-based index. If growth stocks are out of favor, sectors that are larger in a growth index may underperform, leading to Fund underperformance relative to indices less biased toward growth stocks.

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 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. 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, 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.
• The performance shown for Class N Shares for periods prior to May 31, 2012, 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 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 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 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.

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:  2nd Quarter 2009  22.23%          Worst Quarter:  4th Quarter 2008  −25.30%

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 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 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 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 Research 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

0.52%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.16%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.93%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleYear01

664

3 Years

rr_ExpenseExampleYear03

854

5 Years

rr_ExpenseExampleYear05

1,060

10 Years

rr_ExpenseExampleYear10

1,652

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

rr_ExpenseExampleNoRedemptionByYearColumnName

Class A Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

664

3 Years

rr_ExpenseExampleNoRedemptionYear03

854

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,060

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,652

Janus Research 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

0.52%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses

rr_OtherExpensesOverAssets

0.15%

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 Research 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

0.52%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.29%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.06%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleYear01

108

3 Years

rr_ExpenseExampleYear03

337

5 Years

rr_ExpenseExampleYear05

585

10 Years

rr_ExpenseExampleYear10

1,294

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

rr_ExpenseExampleNoRedemptionByYearColumnName

Class S Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

108

3 Years

rr_ExpenseExampleNoRedemptionYear03

337

5 Years

rr_ExpenseExampleNoRedemptionYear05

585

10 Years

rr_ExpenseExampleNoRedemptionYear10

1,294

Janus Research 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

0.52%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.13%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.65%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleYear01

66

3 Years

rr_ExpenseExampleYear03

208

5 Years

rr_ExpenseExampleYear05

362

10 Years

rr_ExpenseExampleYear10

810

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

rr_ExpenseExampleNoRedemptionByYearColumnName

Class I Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

66

3 Years

rr_ExpenseExampleNoRedemptionYear03

208

5 Years

rr_ExpenseExampleNoRedemptionYear05

362

10 Years

rr_ExpenseExampleNoRedemptionYear10

810

Janus Research 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

0.52%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.03%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.55%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class N 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 N Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

56

3 Years

rr_ExpenseExampleNoRedemptionYear03

176

5 Years

rr_ExpenseExampleNoRedemptionYear05

307

10 Years

rr_ExpenseExampleNoRedemptionYear10

689

Janus Research 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

0.52%

Distribution/Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.28%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.80%

Expense Example, By Year, Column [Text]

rr_ExpenseExampleByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleYear01

82

3 Years

rr_ExpenseExampleYear03

255

5 Years

rr_ExpenseExampleYear05

444

10 Years

rr_ExpenseExampleYear10

990

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

rr_ExpenseExampleNoRedemptionByYearColumnName

Class T Shares

1 Year

rr_ExpenseExampleNoRedemptionYear01

82

3 Years

rr_ExpenseExampleNoRedemptionYear03

255

5 Years

rr_ExpenseExampleNoRedemptionYear05

444

10 Years

rr_ExpenseExampleNoRedemptionYear10

990

2005

rr_AnnualReturn2005

6.82%

2006

rr_AnnualReturn2006

8.65%

2007

rr_AnnualReturn2007

24.52%

2008

rr_AnnualReturn2008

(44.36%)

2009

rr_AnnualReturn2009

43.01%

2010

rr_AnnualReturn2010

20.97%

2011

rr_AnnualReturn2011

(3.93%)

2012

rr_AnnualReturn2012

16.63%

2013

rr_AnnualReturn2013

35.12%

2014

rr_AnnualReturn2014

13.96%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter:

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

22.23%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter:

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(25.30%)

Janus Research 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

^[1]

1 Year

rr_AverageAnnualReturnYear01

7.28%

5 Years

rr_AverageAnnualReturnYear05

14.36%

10 Years

rr_AverageAnnualReturnYear10

8.31%

Since Inception

rr_AverageAnnualReturnSinceInception

10.80%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 03, 1993

Janus Research 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

^[2]

1 Year

rr_AverageAnnualReturnYear01

11.99%

5 Years

rr_AverageAnnualReturnYear05

14.85%

10 Years

rr_AverageAnnualReturnYear10

8.14%

Since Inception

rr_AverageAnnualReturnSinceInception

10.34%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 03, 1993

Janus Research 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

13.65%

5 Years

rr_AverageAnnualReturnYear05

15.55%

10 Years

rr_AverageAnnualReturnYear10

8.79%

Since Inception

rr_AverageAnnualReturnSinceInception

10.96%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 03, 1993

Janus Research 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

14.10%

5 Years

rr_AverageAnnualReturnYear05

16.04%

10 Years

rr_AverageAnnualReturnYear10

9.15%

Since Inception

rr_AverageAnnualReturnSinceInception

11.33%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 03, 1993

Janus Research 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

14.25%

5 Years

rr_AverageAnnualReturnYear05

15.85%

10 Years

rr_AverageAnnualReturnYear10

9.15%

Since Inception

rr_AverageAnnualReturnSinceInception

11.33%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 03, 1993

Janus Research 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

13.96%

5 Years

rr_AverageAnnualReturnYear05

15.85%

10 Years

rr_AverageAnnualReturnYear10

9.15%

Since Inception

rr_AverageAnnualReturnSinceInception

11.33%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 03, 1993

Janus Research 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

10.39%

5 Years

rr_AverageAnnualReturnYear05

15.02%

10 Years

rr_AverageAnnualReturnYear10

8.73%

Since Inception

rr_AverageAnnualReturnSinceInception

10.04%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 03, 1993

Janus Research 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

^[3]

1 Year

rr_AverageAnnualReturnYear01

10.61%

5 Years

rr_AverageAnnualReturnYear05

12.78%

10 Years

rr_AverageAnnualReturnYear10

7.50%

Since Inception

rr_AverageAnnualReturnSinceInception

9.29%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 03, 1993

Janus Research Fund | Class A, C, S, I, N, 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

rr_AverageAnnualReturnSinceInception

8.79%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 03, 1993

Janus Research Fund | Class A, C, S, I, N, 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

rr_AverageAnnualReturnSinceInception

9.49%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 03, 1993

[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.