Label	Element	Value
Risk Return Abstract	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	JANUS INVESTMENT FUND
Prospectus Date	rr_ProspectusDate	Jan. 28, 2022
Class A C S I N R T Shares | Janus Henderson Forty Fund
Risk Return Abstract	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	<span style="color:#000000;font-family:Times New Roman;font-size:15.20pt;font-weight:bold;margin-left:3pt;">Janus Henderson Forty Fund</span>
Objective [Heading]	rr_ObjectiveHeading	<span style="color:#FFFFFF;font-family:Times New Roman;font-size:10.45pt;font-weight:bold;margin-left:0.0%;text-transform:uppercase;">Investment Objective</span>
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Janus Henderson Forty Fund seeks long-term growth of capital.
Expense [Heading]	rr_ExpenseHeading	<span style="color:#FFFFFF;font-family:Times New Roman;font-size:10.45pt;font-weight:bold;margin-left:0.0%;text-transform:uppercase;">Fees and Expenses of the Fund</span>
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. 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 Henderson 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 97 of the Fund’s Prospectus and in the “Purchases” section on page 82 of the Fund’s Statement of Additional Information. In addition, please see Appendix A – Intermediary Sales Charge Waivers and Discounts. You may also incur brokerage commissions charged by your broker or financial intermediary when buying Class I Shares or Class N Shares of the Fund that are not reflected in the table or in the example below.
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	<span style="font-family:Times New Roman;font-size:9.50pt;font-weight:bold;">Portfolio Turnover:</span>
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 31% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	31.00%
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	<span style="font-family:Times New Roman;font-size:9.50pt;"> 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 </span><span style="font-family:Times New Roman;font-size:9.50pt;">$50,000</span><span style="font-family:Times New Roman;font-size:9.50pt;"> in the Fund or in other Janus Henderson 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 97 of the Fund’s Prospectus and in the “Purchases” section on page 82 of the Fund’s Statement of Additional Information. In addition, please see Appendix A – Intermediary Sales Charge Waivers and Discounts. You may also incur brokerage commissions charged by your broker or financial intermediary when buying Class I Shares or Class N Shares of the Fund that are not reflected in the table or in the example below.</span>
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	$ 50,000
Expense Example [Heading]	rr_ExpenseExampleHeading	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;font-weight:bold;margin-left:3pt;">EXAMPLE:</span>
Expense Example by Year [Heading]	rr_ExpenseExampleByYearHeading	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;"> 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. Class C Shares automatically convert to Class A Shares after eight years. The Example for Class C Shares for the ten-year period reflects the conversion to Class A Shares. Although your actual costs may be higher or lower, based on these assumptions your costs would be:</span>
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	<span style="color:#FFFFFF;font-family:Times New Roman;font-size:10.45pt;font-weight:bold;margin-left:0.0%;text-transform:uppercase;">Principal investment strategies</span>
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Fund pursues its investment objective by normally investing primarily in a core group of 30-40 common stocks selected for their growth potential. The Fund may invest in companies of any size, but will invest primarily in larger, well-established companies. The Fund may also invest in foreign securities, which may include investments in emerging markets. The Fund is classified as non-diversified, which allows it to hold larger positions in a smaller number of companies, compared to a fund that is classified as diversified. As of September 30, 2021, the Fund held stocks of 39 companies. Of these holdings, 30 comprised approximately 91.16% of the Fund’s holdings.The portfolio managers apply a “bottom up” approach that focuses on fundamental research and considers, among other factors, a company’s sustainable competitive advantages, long-term growth potential, and shareholder value. The Fund generally sells a security when, in the portfolio managers’ opinion, there is a deterioration in a company’s financials, the investment thesis for owning the position has changed, or if the security exceeds its targeted value.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	<span style="color:#FFFFFF;font-family:Times New Roman;font-size:10.45pt;font-weight:bold;margin-left:0.0%;text-transform:uppercase;">Principal investment risks</span>
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. The principal risks associated with investing in the Fund are set forth below.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. Market risk may affect a single issuer, industry, economic sector, or the market as a whole. Market risk may be magnified if certain social, political, economic, and other conditions and events (such as terrorism, conflicts, social unrest, natural disasters, epidemics and pandemics, including COVID-19) adversely interrupt the global economy and financial markets.Portfolio 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.Growth Securities Risk. The Fund invests in companies that the portfolio managers believe have 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.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.Issuer Concentration Risk.  The Fund’s portfolio may be comprised of a relatively small number of issuers in comparison to other funds. As a result, the Fund may be subject to greater risks than a fund that invests in a greater number of issuers. A change in the value of any single investment held by the Fund may affect the overall value of the Fund more than it would affect a fund that holds more investments. In particular, the Fund may be more susceptible to adverse developments affecting any single issuer in the Fund and may be susceptible to greater losses because of these developments.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 or more established 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 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, if any, 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.Industry and Sector Risk. Although the Fund does not concentrate its investments in specific industries or industry sectors, it may have a significant portion of its assets invested in securities of companies conducting similar business, or business within the same economic sector. Companies in the same industry or economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments than funds that invest more broadly. As the Fund’s portfolio becomes more concentrated, the Fund is less able to spread risk and potentially reduce the risk of loss and volatility. In addition, the Fund may be overweight or underweight in certain industries or sectors relative to its benchmark index, which may cause the Fund’s performance to be more or less sensitive to developments affecting those sectors.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	<span style="font-family:Times New Roman;font-size:9.50pt;">The biggest risk is that the Fund’s returns will vary, and you could lose money.</span>
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;font-style:italic;">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.</span>
Risk Nondiversified Status [Text]	rr_RiskNondiversifiedStatus	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;font-style:italic;font-weight:bold;">Nondiversification Risk.</span><span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;"> 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.</span>
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	<span style="color:#FFFFFF;font-family:Times New Roman;font-size:10.45pt;font-weight:bold;margin-left:0.0%;text-transform:uppercase;">Performance information</span>
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 (the “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 the 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 a broad-based securities market index, as well as to one or more supplemental indices that have investment characteristics similar to those of the Fund. 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 janushenderson.com/performance or by calling 1-877-335-2687.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	<span style="font-family:Times New Roman;font-size:9.50pt;">The bar chart depicts the change in performance from year to year during the periods indicated. </span><span style="font-family:Times New Roman;font-size:9.50pt;">The bar chart figures do not </span><span style="font-family:Times New Roman;font-size:9.50pt;">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.</span><span style="font-family:Times New Roman;font-size:9.50pt;"> The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index, as well as to one or more supplemental indices that have investment characteristics similar to those of the Fund. All figures assume reinvestment of dividends and distributions.</span>
Performance Additional Market Index [Text]	rr_PerformanceAdditionalMarketIndex	<span style="font-family:Times New Roman;font-size:9.50pt;"> The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index, as well as to one or more supplemental indices that have investment characteristics similar to those of the Fund. All figures assume reinvestment of dividends and distributions.</span>
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;font-style:italic;">1-877-335-2687</span>
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;font-style:italic;"> janushenderson.com/performance</span>
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;font-style:italic;">The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.</span>
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	<span style="font-family:Times New Roman;font-size:9.50pt;">The bar chart figures do not </span><span style="font-family:Times New Roman;font-size:9.50pt;">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.</span>
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best Quarter:2nd Quarter 202026.53%Worst Quarter:4th Quarter 2018– 14.69%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns (periods ended 12/31/21)
Performance Table Does Reflect Sales Loads	rr_PerformanceTableDoesReflectSalesLoads	<span style="color:#000000;font-family:Times New Roman;font-size:7.60pt;">The one year return is calculated to include the contingent deferred sales charge.</span>
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;"> 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. </span>
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">Actual </span><span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">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-advantaged account, such as a 401(k) plan or an IRA.</span>
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">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.</span>
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The Fund’s primary benchmark index is the Russell 1000 Growth Index. The Fund also compares its performance to the S&P 500 Index. The Russell 1000 Growth Index is used to calculate the Fund’s performance fee adjustment. The indices are described below.•The Russell 1000 Growth Index measures the performance of those Russell 1000 companies with higher price-to-book ratios and higher forecasted growth values.•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-advantaged 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 janushenderson.com/performance or by calling 1-877-335-2687.
Class A C S I N R T Shares | Janus Henderson Forty Fund | Class A
Risk Return Abstract	rr_RiskReturnAbstract
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
Management Fees	rr_ManagementFeesOverAssets	0.68%	[1]
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.09%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.02%
1 Year	rr_ExpenseExampleYear01	$ 673
3 Years	rr_ExpenseExampleYear03	881
5 Years	rr_ExpenseExampleYear05	1,106
10 Years	rr_ExpenseExampleYear10	1,751
1 Year	rr_ExpenseExampleNoRedemptionYear01	673
3 Years	rr_ExpenseExampleNoRedemptionYear03	881
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,106
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,751
Class A C S I N R T Shares | Janus Henderson Forty Fund | Class C
Risk Return Abstract	rr_RiskReturnAbstract
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%
Management Fees	rr_ManagementFeesOverAssets	0.68%	[1]
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	0.09%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.77%
1 Year	rr_ExpenseExampleYear01	$ 280
3 Years	rr_ExpenseExampleYear03	557
5 Years	rr_ExpenseExampleYear05	959
10 Years	rr_ExpenseExampleYear10	1,886
1 Year	rr_ExpenseExampleNoRedemptionYear01	180
3 Years	rr_ExpenseExampleNoRedemptionYear03	557
5 Years	rr_ExpenseExampleNoRedemptionYear05	959
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,886
Class A C S I N R T Shares | Janus Henderson Forty Fund | Class S
Risk Return Abstract	rr_RiskReturnAbstract
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
Management Fees	rr_ManagementFeesOverAssets	0.68%	[1]
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.27%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.20%
1 Year	rr_ExpenseExampleYear01	$ 122
3 Years	rr_ExpenseExampleYear03	381
5 Years	rr_ExpenseExampleYear05	660
10 Years	rr_ExpenseExampleYear10	1,455
1 Year	rr_ExpenseExampleNoRedemptionYear01	122
3 Years	rr_ExpenseExampleNoRedemptionYear03	381
5 Years	rr_ExpenseExampleNoRedemptionYear05	660
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,455
2012	rr_AnnualReturn2012	23.65%
2013	rr_AnnualReturn2013	31.73%
2014	rr_AnnualReturn2014	8.57%
2015	rr_AnnualReturn2015	11.75%
2016	rr_AnnualReturn2016	1.92%
2017	rr_AnnualReturn2017	29.10%
2018	rr_AnnualReturn2018	1.04%
2019	rr_AnnualReturn2019	36.30%
2020	rr_AnnualReturn2020	38.60%
2021	rr_AnnualReturn2021	22.48%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2020
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	26.53%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2018
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(14.69%)
Class A C S I N R T Shares | Janus Henderson Forty Fund | Class I
Risk Return Abstract	rr_RiskReturnAbstract
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
Management Fees	rr_ManagementFeesOverAssets	0.68%	[1]
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.09%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.77%
1 Year	rr_ExpenseExampleYear01	$ 79
3 Years	rr_ExpenseExampleYear03	246
5 Years	rr_ExpenseExampleYear05	428
10 Years	rr_ExpenseExampleYear10	954
1 Year	rr_ExpenseExampleNoRedemptionYear01	79
3 Years	rr_ExpenseExampleNoRedemptionYear03	246
5 Years	rr_ExpenseExampleNoRedemptionYear05	428
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 954
Class A C S I N R T Shares | Janus Henderson Forty Fund | Class N
Risk Return Abstract	rr_RiskReturnAbstract
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
Management Fees	rr_ManagementFeesOverAssets	0.68%	[1]
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.02%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.70%
1 Year	rr_ExpenseExampleYear01	$ 72
3 Years	rr_ExpenseExampleYear03	224
5 Years	rr_ExpenseExampleYear05	390
10 Years	rr_ExpenseExampleYear10	871
1 Year	rr_ExpenseExampleNoRedemptionYear01	72
3 Years	rr_ExpenseExampleNoRedemptionYear03	224
5 Years	rr_ExpenseExampleNoRedemptionYear05	390
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 871
Class A C S I N R T Shares | Janus Henderson Forty Fund | Class R
Risk Return Abstract	rr_RiskReturnAbstract
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
Management Fees	rr_ManagementFeesOverAssets	0.68%	[1]
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.50%
Other Expenses	rr_OtherExpensesOverAssets	0.27%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.45%
1 Year	rr_ExpenseExampleYear01	$ 148
3 Years	rr_ExpenseExampleYear03	459
5 Years	rr_ExpenseExampleYear05	792
10 Years	rr_ExpenseExampleYear10	1,735
1 Year	rr_ExpenseExampleNoRedemptionYear01	148
3 Years	rr_ExpenseExampleNoRedemptionYear03	459
5 Years	rr_ExpenseExampleNoRedemptionYear05	792
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,735
Class A C S I N R T Shares | Janus Henderson Forty Fund | Class T
Risk Return Abstract	rr_RiskReturnAbstract
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
Management Fees	rr_ManagementFeesOverAssets	0.68%	[1]
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.27%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.95%
1 Year	rr_ExpenseExampleYear01	$ 97
3 Years	rr_ExpenseExampleYear03	303
5 Years	rr_ExpenseExampleYear05	525
10 Years	rr_ExpenseExampleYear10	1,166
1 Year	rr_ExpenseExampleNoRedemptionYear01	97
3 Years	rr_ExpenseExampleNoRedemptionYear03	303
5 Years	rr_ExpenseExampleNoRedemptionYear05	525
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,166
Class A C S I N R T Shares | Janus Henderson Forty Fund | Return Before Taxes | Class A
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	15.60%	[2]
5 Years	rr_AverageAnnualReturnYear05	23.41%	[2]
10 Years	rr_AverageAnnualReturnYear10	19.19%	[2]
Since Inception	rr_AverageAnnualReturnSinceInception	12.94%	[2]
Inception Date	rr_AverageAnnualReturnInceptionDate	May 01, 1997	[2]
Class A C S I N R T Shares | Janus Henderson Forty Fund | Return Before Taxes | Class C
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	20.90%	[3]
5 Years	rr_AverageAnnualReturnYear05	24.09%	[3]
10 Years	rr_AverageAnnualReturnYear10	19.13%	[3]
Since Inception	rr_AverageAnnualReturnSinceInception	12.51%	[3]
Inception Date	rr_AverageAnnualReturnInceptionDate	May 01, 1997	[3]
Class A C S I N R T Shares | Janus Henderson Forty Fund | Return Before Taxes | Class S
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	22.48%
5 Years	rr_AverageAnnualReturnYear05	24.72%
10 Years	rr_AverageAnnualReturnYear10	19.78%
Since Inception	rr_AverageAnnualReturnSinceInception	13.09%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 01, 1997
Class A C S I N R T Shares | Janus Henderson Forty Fund | Return Before Taxes | Class I
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	22.98%
5 Years	rr_AverageAnnualReturnYear05	25.25%
10 Years	rr_AverageAnnualReturnYear10	20.26%
Since Inception	rr_AverageAnnualReturnSinceInception	13.41%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 01, 1997
Class A C S I N R T Shares | Janus Henderson Forty Fund | Return Before Taxes | Class N
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	23.08%
5 Years	rr_AverageAnnualReturnYear05	25.33%
10 Years	rr_AverageAnnualReturnYear10	20.33%
Since Inception	rr_AverageAnnualReturnSinceInception	13.30%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 01, 1997
Class A C S I N R T Shares | Janus Henderson Forty Fund | Return Before Taxes | Class R
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	22.20%
5 Years	rr_AverageAnnualReturnYear05	24.41%
10 Years	rr_AverageAnnualReturnYear10	19.46%
Since Inception	rr_AverageAnnualReturnSinceInception	12.82%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 01, 1997
Class A C S I N R T Shares | Janus Henderson Forty Fund | Return Before Taxes | Class T
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	22.78%
5 Years	rr_AverageAnnualReturnYear05	25.04%
10 Years	rr_AverageAnnualReturnYear10	20.07%
Since Inception	rr_AverageAnnualReturnSinceInception	13.23%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 01, 1997
Class A C S I N R T Shares | Janus Henderson Forty Fund | Return After Taxes on Distributions | Class S
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	19.64%
5 Years	rr_AverageAnnualReturnYear05	21.97%
10 Years	rr_AverageAnnualReturnYear10	16.35%
Since Inception	rr_AverageAnnualReturnSinceInception	11.68%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 01, 1997
Class A C S I N R T Shares | Janus Henderson Forty Fund | Return After Taxes on Distributions and Sale of Fund Shares | Class S
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	15.15%
5 Years	rr_AverageAnnualReturnYear05	19.54%
10 Years	rr_AverageAnnualReturnYear10	15.33%
Since Inception	rr_AverageAnnualReturnSinceInception	11.12%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 01, 1997
Class A C S I N R T Shares | Janus Henderson Forty Fund | S&P 500® Index (reflects no deduction for expenses, fees, or taxes) | Class A
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	28.71%
5 Years	rr_AverageAnnualReturnYear05	18.47%
10 Years	rr_AverageAnnualReturnYear10	16.55%
Since Inception	rr_AverageAnnualReturnSinceInception	9.53%
Class A C S I N R T Shares | Janus Henderson Forty Fund | S&P 500® Index (reflects no deduction for expenses, fees, or taxes) | Class C
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	28.71%
5 Years	rr_AverageAnnualReturnYear05	18.47%
10 Years	rr_AverageAnnualReturnYear10	16.55%
Since Inception	rr_AverageAnnualReturnSinceInception	9.53%
Class A C S I N R T Shares | Janus Henderson Forty Fund | S&P 500® Index (reflects no deduction for expenses, fees, or taxes) | Class S
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	28.71%
5 Years	rr_AverageAnnualReturnYear05	18.47%
10 Years	rr_AverageAnnualReturnYear10	16.55%
Since Inception	rr_AverageAnnualReturnSinceInception	9.53%
Class A C S I N R T Shares | Janus Henderson Forty Fund | S&P 500® Index (reflects no deduction for expenses, fees, or taxes) | Class I
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	28.71%
5 Years	rr_AverageAnnualReturnYear05	18.47%
10 Years	rr_AverageAnnualReturnYear10	16.55%
Since Inception	rr_AverageAnnualReturnSinceInception	9.53%
Class A C S I N R T Shares | Janus Henderson Forty Fund | S&P 500® Index (reflects no deduction for expenses, fees, or taxes) | Class N
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	28.71%
5 Years	rr_AverageAnnualReturnYear05	18.47%
10 Years	rr_AverageAnnualReturnYear10	16.55%
Since Inception	rr_AverageAnnualReturnSinceInception	9.53%
Class A C S I N R T Shares | Janus Henderson Forty Fund | S&P 500® Index (reflects no deduction for expenses, fees, or taxes) | Class R
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	28.71%
5 Years	rr_AverageAnnualReturnYear05	18.47%
10 Years	rr_AverageAnnualReturnYear10	16.55%
Since Inception	rr_AverageAnnualReturnSinceInception	9.53%
Class A C S I N R T Shares | Janus Henderson Forty Fund | S&P 500® Index (reflects no deduction for expenses, fees, or taxes) | Class T
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	28.71%
5 Years	rr_AverageAnnualReturnYear05	18.47%
10 Years	rr_AverageAnnualReturnYear10	16.55%
Since Inception	rr_AverageAnnualReturnSinceInception	9.53%
Class A C S I N R T Shares | Janus Henderson Forty Fund | Russell 1000® Growth Index (reflects no deduction for expenses, fees, or taxes) | Class A
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	27.60%
5 Years	rr_AverageAnnualReturnYear05	25.32%
10 Years	rr_AverageAnnualReturnYear10	19.79%
Since Inception	rr_AverageAnnualReturnSinceInception	10.18%
Class A C S I N R T Shares | Janus Henderson Forty Fund | Russell 1000® Growth Index (reflects no deduction for expenses, fees, or taxes) | Class C
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	27.60%
5 Years	rr_AverageAnnualReturnYear05	25.32%
10 Years	rr_AverageAnnualReturnYear10	19.79%
Since Inception	rr_AverageAnnualReturnSinceInception	10.18%
Class A C S I N R T Shares | Janus Henderson Forty Fund | Russell 1000® Growth Index (reflects no deduction for expenses, fees, or taxes) | Class S
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	27.60%
5 Years	rr_AverageAnnualReturnYear05	25.32%
10 Years	rr_AverageAnnualReturnYear10	19.79%
Since Inception	rr_AverageAnnualReturnSinceInception	10.18%
Class A C S I N R T Shares | Janus Henderson Forty Fund | Russell 1000® Growth Index (reflects no deduction for expenses, fees, or taxes) | Class I
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	27.60%
5 Years	rr_AverageAnnualReturnYear05	25.32%
10 Years	rr_AverageAnnualReturnYear10	19.79%
Since Inception	rr_AverageAnnualReturnSinceInception	10.18%
Class A C S I N R T Shares | Janus Henderson Forty Fund | Russell 1000® Growth Index (reflects no deduction for expenses, fees, or taxes) | Class N
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	27.60%
5 Years	rr_AverageAnnualReturnYear05	25.32%
10 Years	rr_AverageAnnualReturnYear10	19.79%
Since Inception	rr_AverageAnnualReturnSinceInception	10.18%
Class A C S I N R T Shares | Janus Henderson Forty Fund | Russell 1000® Growth Index (reflects no deduction for expenses, fees, or taxes) | Class R
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	27.60%
5 Years	rr_AverageAnnualReturnYear05	25.32%
10 Years	rr_AverageAnnualReturnYear10	19.79%
Since Inception	rr_AverageAnnualReturnSinceInception	10.18%
Class A C S I N R T Shares | Janus Henderson Forty Fund | Russell 1000® Growth Index (reflects no deduction for expenses, fees, or taxes) | Class T
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	27.60%
5 Years	rr_AverageAnnualReturnYear05	25.32%
10 Years	rr_AverageAnnualReturnYear10	19.79%
Since Inception	rr_AverageAnnualReturnSinceInception	10.18%

[1] This fee may adjust up or down monthly based on the Fund’s performance relative to its benchmark index over the performance measurement period. For more information regarding performance-based advisory fees, refer to “Management Expenses” in the Fund’s Prospectus.

[2] Calculated assuming maximum permitted sales loads.

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