Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	JANUS INVESTMENT FUND
Prospectus Date	rr_ProspectusDate	Jan. 26, 2018
Janus Henderson U.S. Growth Opportunities Fund | Class A, C, S, I, N, T Shares
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	FUND SUMMARY Janus Henderson U.S. Growth Opportunities Fund
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Janus Henderson U.S. Growth Opportunities Fund seeks long-term capital appreciation.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE FUND
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	SHAREHOLDER FEES (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	February 1, 2019
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. The portfolio turnover rate of Henderson US Growth Opportunities Fund (the “Predecessor Fund”) and the Fund for the fiscal year August 1, 2016 to July 31, 2017 was 27% of the average value of the portfolio. The portfolio turnover rate of the Fund for the fiscal period August 1, 2017 to September 30, 2017 was 2% of the average value of the portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	2.00%
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 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 96 of the Fund’s Prospectus and in the “Purchases” section on page 84 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 N Shares of the Fund that are not reflected in the table or in the example below.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	$ 50,000
Expenses Restated to Reflect Current [Text]	rr_ExpensesRestatedToReflectCurrent	Other Expenses have been restated to reflect the estimated expenses that the Fund expects to incur.
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE:
Expense Example by Year [Heading]	rr_ExpenseExampleByYearHeading	The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses without waivers remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following Example is based on expenses without waivers. The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.
Expense Example by, Year, Caption [Text]	rr_ExpenseExampleByYearCaption	If Shares are redeemed:
Expense Example, No Redemption, By Year, Caption [Text]	rr_ExpenseExampleNoRedemptionByYearCaption	If Shares are not redeemed:
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Fund pursues its investment objective by investing, under normal circumstances, at least 80% of its net assets (plus any borrowings for investment purposes) in equity securities of U.S. companies. The Fund seeks to invest primarily in common stocks of U.S. companies of any market capitalization. In selecting stocks, the Fund uses bottom-up, fundamental analysis to identify companies with strong growth characteristics and experienced management. Security selection is based upon an analysis of the earnings growth prospects of a company, the quality of a company’s management, and the unique competitive advantages of a company. The Fund’s bottom-up approach is supplemented with top-down considerations. The Fund may also invest in securities issued by smaller companies and in less seasoned issuers. The Fund generally sells a stock when, in the portfolio managers’ opinion, there is deterioration in the company’s fundamentals or if the security is no longer attractively valued. Investments may also be sold if the portfolio managers believe a higher conviction investment opportunity arises. There is no limitation on the market capitalization range of companies in which the Fund may invest. The Fund may invest a significant portion of its assets in smaller and less seasoned issuers. The Fund may also, from time to time, invest in exchange-traded funds (“ETFs”).
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 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. Sector Risk.  At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business within an economic sector. Companies in the same economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that economic sector 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. Small- and Mid-Sized Companies Risk.  The Fund’s investments in securities issued by small- and mid-sized companies, which can include smaller, start-up companies offering emerging products or services, may involve greater risks than are customarily associated with larger, more established companies. For example, while small- and mid-sized companies may realize more substantial growth than larger or more established issuers, they may also suffer more significant losses as a result of their narrow product lines, limited operating history, greater exposure to competitive threats, limited financial resources, limited trading markets, and the potential lack of management depth. Securities issued by small- and mid-sized companies tend to be more volatile and somewhat more speculative than securities issued by larger or more established companies and may underperform as compared to the securities of larger or more established companies. These holdings are also subject to wider price fluctuations and tend to be less liquid than stocks of larger or more established companies, which could have a significant adverse effect on the Fund’s returns, especially as market conditions change. 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. Exchange-Traded Funds Risk.  The Fund may invest in ETFs to gain exposure to a particular portion of the market. ETFs are typically open-end investment companies, which may seek to track the performance of a specific index or be actively managed. ETFs are traded on a national securities exchange at market prices that may vary from the net asset value of their underlying investments. Accordingly, there may be times when an ETF trades at a premium or discount. When the Fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF’s expenses. The Fund is also subject to the risks associated with the securities in which the ETF invests. 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. Returns shown prior to June 5, 2017 are those of the Predecessor Fund, Henderson US Growth Opportunities Fund. The Predecessor Fund was advised by Henderson Global Investors (North America) Inc. and subadvised by Geneva. Class A Shares, Class C Shares, Class I Shares and Class R6 Shares of the Predecessor Fund were reorganized into Class A Shares, Class C Shares, Class I Shares and Class N Shares, respectively, of the Fund on June 2, 2017. Class A Shares, Class C Shares and Class I Shares of the Predecessor Fund commenced operations with the Predecessor Fund’s inception on December 18, 2014. Class R6 Shares of the Predecessor Fund commenced operations on November 30, 2015. Class S Shares and Class T Shares of the Fund commenced operations on June 5, 2017. The performance shown for Class A Shares prior to June 5, 2017 reflects the performance of Class A Shares of the Predecessor Fund and is calculated using the fees and expenses of Class A Shares of the Predecessor Fund, in effect during the periods shown, net of any applicable fee and expense limitations or waivers. The performance shown for Class C Shares prior to June 5, 2017 reflects the performance of Class C Shares of the Predecessor Fund and is calculated using the fees and expenses of Class C Shares of the Predecessor Fund, in effect during the periods shown, net of any applicable fee and expense limitations or waivers. The performance shown for Class I Shares prior to June 5, 2017 reflects the performance of Class I Shares of the Predecessor Fund and is calculated using the fees and expenses of Class I Shares of the Predecessor Fund, in effect during the periods shown, net of any applicable fee and expense limitations or waivers. The performance shown for Class N Shares prior to June 5, 2017 reflects the performance of Class R6 Shares of the Predecessor Fund and is calculated using the fees and expenses of R6 Shares of the Predecessor Fund, in effect during the periods shown, net of any applicable fee and expense limitations or waivers, except that for periods prior to November 30, 2015, performance shown for Class N Shares reflects the performance of Class I Shares of the Predecessor Fund, calculated using the estimated fees and expenses of Class N Shares, net of any applicable fee and expense limitations or waivers. The performance shown for Class S Shares prior to June 5, 2017 reflects the performance of Class I Shares of the Predecessor Fund, calculated using the estimated fees and expenses of Class S Shares, net of any applicable fee and expense limitations or waivers. The performance shown for Class T Shares prior to June 5, 2017 reflects the performance of Class I Shares of the Predecessor Fund, calculated using the estimated fees and expenses of Class T Shares, net of any applicable fee and expense limitations or waivers. Returns of the Fund will be different from the Predecessor Fund as they have different expenses. 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. 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 (and the Predecessor Fund’s) past performance (before and after taxes) does not necessarily indicate how the Fund 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	The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. The bar chart depicts the change in performance from year to year during the periods indicated.
Performance Additional Market Index [Text]	rr_PerformanceAdditionalMarketIndex	The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. 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	janushenderson.com/performance
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Fund’s (and the Predecessor Fund’s) past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Annual Total Returns for Class I Shares (calendar year-end)
Bar Chart Does Not Reflect Sales Loads [Text]	rr_BarChartDoesNotReflectSalesLoads	The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best Quarter:  1st Quarter 2017  6.63%          Worst Quarter:  3rd Quarter 2015  – 3.36%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns (periods ended 12/31/17)
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The Fund’s primary benchmark index is the Russell 3000® Growth Index. The index is described below. The Russell 3000® Growth Index is an unmanaged market capitalization weighted index of common stock prices that measures the performance of the broad growth segment of the U.S. equity universe. It includes those Russell 3000® Index companies with higher price-to-book ratios and higher forecasted growth values. The Russell 3000® Index measures the performance of the largest 3000 U.S. companies representing approximately 98% of the investable U.S. equity market. It is not possible to invest directly in an index. After-tax returns are calculated using distributions for the Predecessor Fund’s Class I Shares for the period prior to June 5, 2017. If Class I Shares of the Fund had been available during periods prior to June 5, 2017, the distributions used to calculate the after-tax returns may have been different. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA. After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.
Performance Table Closing [Text Block]	rr_PerformanceTableClosingTextBlock	Updated performance information is available at janushenderson.com/performance or by calling 1-877-335-2687.
Janus Henderson U.S. Growth Opportunities Fund | Class A, C, S, I, N, T Shares | Class A
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	Class A
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	5.75%
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class A
Management Fees	rr_ManagementFeesOverAssets	0.75%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	1.62%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.62%	[2]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	1.48%	[2]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.14%	[2]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class A Shares
1 Year	rr_ExpenseExampleYear01	$ 825
3 Years	rr_ExpenseExampleYear03	1,343
5 Years	rr_ExpenseExampleYear05	1,885
10 Years	rr_ExpenseExampleYear10	$ 3,359
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class A Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 825
3 Years	rr_ExpenseExampleNoRedemptionYear03	1,343
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,885
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 3,359
Janus Henderson U.S. Growth Opportunities Fund | Class A, C, S, I, N, T Shares | Class C
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	Class C
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	1.00%
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class C
Management Fees	rr_ManagementFeesOverAssets	0.75%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	1.58%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	3.33%	[2]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	1.48%	[2]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.85%	[2]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class C Shares
1 Year	rr_ExpenseExampleYear01	$ 436
3 Years	rr_ExpenseExampleYear03	1,024
5 Years	rr_ExpenseExampleYear05	1,736
10 Years	rr_ExpenseExampleYear10	$ 3,622
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class C Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 336
3 Years	rr_ExpenseExampleNoRedemptionYear03	1,024
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,736
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 3,622
Janus Henderson U.S. Growth Opportunities Fund | Class A, C, S, I, N, T Shares | Class S
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	Class S
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class S
Management Fees	rr_ManagementFeesOverAssets	0.75%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	1.78%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.78%	[2]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	1.46%	[2]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.32%	[2]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class S Shares
1 Year	rr_ExpenseExampleYear01	$ 281
3 Years	rr_ExpenseExampleYear03	862
5 Years	rr_ExpenseExampleYear05	1,469
10 Years	rr_ExpenseExampleYear10	$ 3,109
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class S Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 281
3 Years	rr_ExpenseExampleNoRedemptionYear03	862
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,469
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 3,109
Janus Henderson U.S. Growth Opportunities Fund | Class A, C, S, I, N, T Shares | Class I
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	Class I
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class I
Management Fees	rr_ManagementFeesOverAssets	0.75%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	1.60%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.35%	[2]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	1.49%	[2]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	0.86%	[2]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class I Shares
1 Year	rr_ExpenseExampleYear01	$ 238
3 Years	rr_ExpenseExampleYear03	733
5 Years	rr_ExpenseExampleYear05	1,255
10 Years	rr_ExpenseExampleYear10	$ 2,686
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class I Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 238
3 Years	rr_ExpenseExampleNoRedemptionYear03	733
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,255
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 2,686
2015	rr_AnnualReturn2015	7.35%
2016	rr_AnnualReturn2016	1.85%
2017	rr_AnnualReturn2017	19.36%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Mar. 31, 2017
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	6.63%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2015
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(3.36%)
Janus Henderson U.S. Growth Opportunities Fund | Class A, C, S, I, N, T Shares | Class N
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	Class N
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class N
Management Fees	rr_ManagementFeesOverAssets	0.75%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	1.53%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.28%	[2]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	1.45%	[2]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	0.83%	[2]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class N Shares
1 Year	rr_ExpenseExampleYear01	$ 231
3 Years	rr_ExpenseExampleYear03	712
5 Years	rr_ExpenseExampleYear05	1,220
10 Years	rr_ExpenseExampleYear10	$ 2,615
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class N Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 231
3 Years	rr_ExpenseExampleNoRedemptionYear03	712
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,220
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 2,615
Janus Henderson U.S. Growth Opportunities Fund | Class A, C, S, I, N, T Shares | Class T
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	Class T
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class T
Management Fees	rr_ManagementFeesOverAssets	0.75%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	1.72%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.47%	[2]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	1.41%	[2]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.06%	[2]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class T Shares
1 Year	rr_ExpenseExampleYear01	$ 250
3 Years	rr_ExpenseExampleYear03	770
5 Years	rr_ExpenseExampleYear05	1,316
10 Years	rr_ExpenseExampleYear10	$ 2,806
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class T Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 250
3 Years	rr_ExpenseExampleNoRedemptionYear03	770
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,316
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 2,806
Janus Henderson U.S. Growth Opportunities Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class A
Risk/Return:	rr_RiskReturnAbstract
Column	rr_AverageAnnualReturnColumnName	Class A Shares
Label	rr_AverageAnnualReturnLabel	Return Before Taxes	[3]
1 Year	rr_AverageAnnualReturnYear01	12.32%
Since Inception	rr_AverageAnnualReturnSinceInception	7.06%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 18, 2014
Janus Henderson U.S. Growth Opportunities Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class C
Risk/Return:	rr_RiskReturnAbstract
Column	rr_AverageAnnualReturnColumnName	Class C Shares
Label	rr_AverageAnnualReturnLabel	Return Before Taxes	[4]
1 Year	rr_AverageAnnualReturnYear01	17.38%
Since Inception	rr_AverageAnnualReturnSinceInception	8.36%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 18, 2014
Janus Henderson U.S. Growth Opportunities 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	18.33%
Since Inception	rr_AverageAnnualReturnSinceInception	7.58%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 18, 2014
Janus Henderson U.S. Growth Opportunities 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	19.36%
Since Inception	rr_AverageAnnualReturnSinceInception	9.42%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 18, 2014
Janus Henderson U.S. Growth Opportunities 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	19.18%
Since Inception	rr_AverageAnnualReturnSinceInception	8.76%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 18, 2014
Janus Henderson U.S. Growth Opportunities 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	18.61%
Since Inception	rr_AverageAnnualReturnSinceInception	7.84%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 18, 2014
Janus Henderson U.S. Growth Opportunities Fund | Class A, C, S, I, N, T Shares | Return After Taxes on Distributions | Class I
Risk/Return:	rr_RiskReturnAbstract
Column	rr_AverageAnnualReturnColumnName	Class I Shares
Label	rr_AverageAnnualReturnLabel	Return After Taxes on Distributions
1 Year	rr_AverageAnnualReturnYear01	19.14%
Since Inception	rr_AverageAnnualReturnSinceInception	9.35%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 18, 2014
Janus Henderson U.S. Growth Opportunities Fund | Class A, C, S, I, N, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class I
Risk/Return:	rr_RiskReturnAbstract
Column	rr_AverageAnnualReturnColumnName	Class I Shares
Label	rr_AverageAnnualReturnLabel	Return After Taxes on Distributions and Sale of Fund Shares
1 Year	rr_AverageAnnualReturnYear01	11.14%
Since Inception	rr_AverageAnnualReturnSinceInception	7.33%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 18, 2014
Janus Henderson U.S. Growth Opportunities Fund | Class A, C, S, I, N, T Shares | Russell 3000® Growth Index (reflects no deduction for expenses, fees, or taxes)
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Russell 3000® Growth Index
1 Year	rr_AverageAnnualReturnYear01	29.59%
Since Inception	rr_AverageAnnualReturnSinceInception	13.32%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 18, 2014

[1] Other Expenses have been restated to reflect the estimated expenses that the Fund expects to incur.

[2] Janus Capital has contractually agreed to waive its investment advisory fee and/or reimburse operating expenses to the extent that the Fund’s total annual fund operating expenses (excluding the fees payable pursuant to a Rule 12b-1 plan, shareholder servicing fees, such as transfer agency fees (including out-of-pocket costs), administrative services fees and any networking/omnibus/administrative fees payable by any share class; brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) exceed 0.80% until at least February 1, 2019. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

[3] Calculated assuming maximum permitted sales loads.

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