Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	JANUS INVESTMENT FUND
Prospectus Date	rr_ProspectusDate	Jan. 28, 2020
Janus Henderson Global Real Estate Fund | Class A, C, S, I, N, T Shares
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	FUND SUMMARY Janus Henderson Global Real Estate Fund
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Janus Henderson Global Real Estate Fund seeks total return through a combination of capital appreciation and current income.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE FUND
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	SHAREHOLDER FEES (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	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 any performance adjustments to management fees, 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 0.91% for at least a one-year period commencing on January 28, 2020. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover:
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 61% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	61.00%
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus 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 148 of the Fund’s Prospectus and in the “Purchases” section on page 85 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.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	$ 50,000
Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]	rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees	“Acquired Fund” refers to any underlying fund (including, but not limited to, exchange-traded funds) in which a fund invests or has invested during the period. Acquired fund fees and expenses are indirect expenses a fund may incur as a result of investing in shares of an underlying fund. To the extent that the Fund invests in Acquired Funds, the Fund’s “Total Annual Fund Operating Expenses” may not correlate to the “Ratio of gross expenses to average net assets” presented in the Financial Highlights tables because that ratio includes only the direct operating expenses incurred by the Fund, not the indirect costs of investing in Acquired Funds.
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 real estate-related companies. Such companies may include those in the real estate industry or real estate-related industries. These securities may include common stocks, preferred stocks, and other equity securities, including, but not limited to, real estate investment trusts (“REITs”) and similar REIT-like entities, such as foreign entities that have REIT characteristics. The Fund may invest in shares of companies through initial public offerings. As a fundamental policy, the Fund will concentrate 25% or more of its net assets in securities of issuers in real estate or real estate-related industries. The Fund’s investment in companies engaged in businesses outside the real estate industry which possess significant real estate holdings will be deemed to be in the real estate industry for purposes of the Fund’s investment objective and its policy on industry concentration. Real estate-related industries are comprised of companies that, in the opinion of the portfolio managers, at the time of investment, generally (i) derive at least 50% of their revenue from ownership, construction, extraction, financing, management, operation, sales or development of real estate, or from businesses which have a clear relationship to these activities; (ii) have at least 50% of their assets in real estate; or (iii) have more than 50% of their net asset value accounted for by real estate. A REIT is a company dedicated to owning, and usually operating, income-producing real estate, or to financing real estate. REITs pool investors’ funds for investment primarily in income-producing real estate or real estate-related loans or interests. Under the Internal Revenue Code of 1986, as amended (the “Internal Revenue Code”), a REIT is not taxed on income it distributes to its shareholders if it complies with several requirements relating to its organization, ownership, assets and income, and a requirement that it generally distributes to its shareholders at least 90% of its taxable income (other than net capital gains) for each taxable year. The Fund also invests in non-U.S. real estate and real estate-related companies. The Fund expects under normal market conditions to maintain investments in issuers that are economically tied to different countries throughout the world, including the United States. The Fund may also invest in companies or issuers that are economically tied to emerging markets. In choosing investments for the Fund, the portfolio managers apply a “bottom up” approach that utilizes the portfolio managers’ knowledge of issuers in the Americas and the Asia Pacific and European regions. The portfolio managers may also apply a “top down” analysis of property markets and sectors, economics, and capital markets in seeking to limit the Fund’s exposures to various risks. 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.
Strategy Portfolio Concentration [Text]	rr_StrategyPortfolioConcentration	As a fundamental policy, the Fund will concentrate 25% or more of its net assets in securities of issuers in real estate or real estate-related industries.
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 interested in investments focused in the real estate industry or real estate-related industries, including common stocks. Common stocks tend to be more volatile than many other investment choices. Real Estate Securities Risk.  An investment in the Fund may be subject to many of the same risks as a direct investment in real estate. The value of real estate-related companies’ securities is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the company. Investments in REITs involve the same risks as other real estate investments. In addition, a REIT could fail to qualify for tax-free pass-through of its income under the Internal Revenue Code or fail to maintain its exemption from registration under the Investment Company Act of 1940, as amended, which could produce adverse economic consequences for the REIT and its investors, including the Fund. Concentration Risk.  Since the Fund concentrates its assets in the real estate or real estate-related industry, an investment in the Fund will be closely linked to performance of the real estate markets. As a result, the Fund may be subject to greater risks and its net asset value may fluctuate more than a fund that does not concentrate its investments. Foreign Exposure Risk.  The Fund normally has significant exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries. Market Risk.  The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money. Market risk may affect a single issuer, industry, economic sector, or the market as a whole. Initial Public Offering Risk.  The Fund’s purchase of shares issued in an initial public offering (“IPO”) exposes it to the risks associated with companies that have little operating history as public companies, as well as to the risks inherent in those sectors of the market where these new issuers operate. Although IPO investments may have had a positive impact on the Fund’s performance in the past, there can be no assurance that the Fund will identify favorable IPO investment opportunities in the future. In addition, as the Fund increases in size, the impact of IPOs on the Fund’s performance will generally decrease. Emerging Markets Risk.  The risks of foreign investing are heightened when investing in emerging markets. Emerging markets securities involve a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. There is a risk in developing countries that a future economic or political crisis could lead to price controls, forced mergers of companies, expropriation or confiscatory taxation, imposition or enforcement of foreign ownership limits, seizure, nationalization, sanctions or imposition of restrictions by various governmental entities on investment and trading, or creation of government monopolies, any of which may have a detrimental effect on the Fund’s investments. In addition, the Fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of the Fund’s investments. To the extent that the Fund invests a significant portion of its assets in the securities of emerging markets issuers in or companies of a single country or region, it is more likely to be impacted by events or conditions affecting that country or region, which could have a negative impact on the Fund’s performance. As of September 30, 2019, approximately 5.6% of the Fund’s investments were in emerging markets (i.e., countries included in the MSCI Emerging Markets IndexSM). 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 I Shares, Class A Shares, Class C Shares, and Class S Shares of the Fund commenced operations on July 6, 2009, after the reorganization of each corresponding class of shares of Janus Adviser Global Real Estate 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 January 26, 2018. The performance shown for Class I Shares, Class A Shares, Class C Shares, and Class S Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund’s Class I Shares, Class A Shares, Class C Shares, and Class S Shares prior to the reorganization, calculated using the fees and expenses of each respective share class of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers. The performance shown for Class T Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund’s Class I Shares prior to the reorganization, calculated using the fees and expenses of Class T Shares, without the effect of any fee and expense limitations or waivers. The performance shown for Class N Shares for periods prior to January 26, 2018, reflects the performance of the Fund’s Class I Shares from July 6, 2009, calculated using the fees and expenses of Class I Shares, net of any applicable fee and expense limitations or waivers. The performance shown for Class N Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund’s Class I Shares, 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. If Class T Shares of the Fund had been available during periods prior to July 6, 2009 or Class N Shares of the Fund had been available during periods prior to January 26, 2018, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class I Shares, Class A Shares, Class C Shares, Class S Shares, Class N Shares, and Class T Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers. The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. 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	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. 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 past performance (before and after taxes) does not necessarily indicate how it will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Annual Total Returns for Class I Shares (calendar year-end)
Bar Chart Does Not Reflect Sales Loads [Text]	rr_BarChartDoesNotReflectSalesLoads	The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best Quarter: 1st Quarter 2012 16.29%          Worst Quarter: 3rd Quarter 2011 – 20.40%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns (periods ended 12/31/19)
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-advantaged 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 FTSE EPRA Nareit Global Index. The primary index is used to calculate the Fund’s performance fee adjustment. The Fund also compares its performance to the FTSE EPRA Nareit Global Net Index (the “Net Index”). Both indices are composed of the same holdings. However, the FTSE EPRA Nareit Global Index reflects no deduction for foreign withholding taxes, whereas the Net Index reflects deduction for such taxes. The indices are described below. The FTSE EPRA Nareit Global Index and the Net Index are global market capitalization-weighted indices composed of listed real estate securities in the North American, European, Asian, and South American real estate markets including both developed and emerging market countries. After-tax returns are calculated using distributions for the Fund’s Class I Shares for periods following July 6, 2009; and for the JAD predecessor fund’s Class I Shares for periods prior to July 6, 2009. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-advantaged 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 Global Real Estate 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	0.85%	[1]
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.26%
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.37%	[3]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	0.01%	[3]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.36%	[3]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class A Shares
1 Year	rr_ExpenseExampleYear01	$ 706
3 Years	rr_ExpenseExampleYear03	984
5 Years	rr_ExpenseExampleYear05	1,282
10 Years	rr_ExpenseExampleYear10	$ 2,127
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class A Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 706
3 Years	rr_ExpenseExampleNoRedemptionYear03	984
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,282
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 2,127
Janus Henderson Global Real Estate 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	0.85%	[1]
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	0.27%
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.13%	[3]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	none	[3]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	2.13%	[3]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class C Shares
1 Year	rr_ExpenseExampleYear01	$ 316
3 Years	rr_ExpenseExampleYear03	667
5 Years	rr_ExpenseExampleYear05	1,144
10 Years	rr_ExpenseExampleYear10	$ 2,462
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class C Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 216
3 Years	rr_ExpenseExampleNoRedemptionYear03	667
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,144
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 2,462
Janus Henderson Global Real Estate 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	0.85%	[1]
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.47%
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.58%	[3]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	0.05%	[3]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.53%	[3]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class S Shares
1 Year	rr_ExpenseExampleYear01	$ 161
3 Years	rr_ExpenseExampleYear03	499
5 Years	rr_ExpenseExampleYear05	860
10 Years	rr_ExpenseExampleYear10	$ 1,878
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class S Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 161
3 Years	rr_ExpenseExampleNoRedemptionYear03	499
5 Years	rr_ExpenseExampleNoRedemptionYear05	860
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,878
Janus Henderson Global Real Estate 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	0.85%	[1]
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.24%
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.10%	[3]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	none	[3]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.10%	[3]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class I Shares
1 Year	rr_ExpenseExampleYear01	$ 112
3 Years	rr_ExpenseExampleYear03	350
5 Years	rr_ExpenseExampleYear05	606
10 Years	rr_ExpenseExampleYear10	$ 1,340
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class I Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 112
3 Years	rr_ExpenseExampleNoRedemptionYear03	350
5 Years	rr_ExpenseExampleNoRedemptionYear05	606
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,340
2010	rr_AnnualReturn2010	21.13%
2011	rr_AnnualReturn2011	(13.54%)
2012	rr_AnnualReturn2012	32.37%
2013	rr_AnnualReturn2013	6.65%
2014	rr_AnnualReturn2014	14.23%
2015	rr_AnnualReturn2015	(1.94%)
2016	rr_AnnualReturn2016	3.50%
2017	rr_AnnualReturn2017	17.72%
2018	rr_AnnualReturn2018	(3.13%)
2019	rr_AnnualReturn2019	30.88%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Mar. 31, 2012
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	16.29%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2011
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(20.40%)
Janus Henderson Global Real Estate 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	0.85%	[1]
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.14%
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.00%	[3]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	none	[3]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.00%	[3]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class N Shares
1 Year	rr_ExpenseExampleYear01	$ 102
3 Years	rr_ExpenseExampleYear03	318
5 Years	rr_ExpenseExampleYear05	552
10 Years	rr_ExpenseExampleYear10	$ 1,225
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class N Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 102
3 Years	rr_ExpenseExampleNoRedemptionYear03	318
5 Years	rr_ExpenseExampleNoRedemptionYear05	552
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,225
Janus Henderson Global Real Estate 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	0.85%	[1]
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.38%
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.24%	[3]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	none	[3]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.24%	[3]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class T Shares
1 Year	rr_ExpenseExampleYear01	$ 126
3 Years	rr_ExpenseExampleYear03	393
5 Years	rr_ExpenseExampleYear05	681
10 Years	rr_ExpenseExampleYear10	$ 1,500
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class T Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 126
3 Years	rr_ExpenseExampleNoRedemptionYear03	393
5 Years	rr_ExpenseExampleNoRedemptionYear05	681
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,500
Janus Henderson Global Real Estate Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class A
Risk/Return:	rr_RiskReturnAbstract
Average Annual Return, Column Name	rr_AverageAnnualReturnColumnName	Class A Shares
Label	rr_AverageAnnualReturnLabel	Return Before Taxes	[4]
1 Year	rr_AverageAnnualReturnYear01	23.12%
5 Years	rr_AverageAnnualReturnYear05	7.12%
10 Years	rr_AverageAnnualReturnYear10	8.90%
Since Inception of Predecessor Fund	rr_AverageAnnualReturnSinceInception	5.88%
Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 28, 2007
Janus Henderson Global Real Estate Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class C
Risk/Return:	rr_RiskReturnAbstract
Average Annual Return, Column Name	rr_AverageAnnualReturnColumnName	Class C Shares
Label	rr_AverageAnnualReturnLabel	Return Before Taxes	[5]
1 Year	rr_AverageAnnualReturnYear01	28.61%
5 Years	rr_AverageAnnualReturnYear05	7.57%
10 Years	rr_AverageAnnualReturnYear10	8.73%
Since Inception of Predecessor Fund	rr_AverageAnnualReturnSinceInception	5.66%
Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 28, 2007
Janus Henderson Global Real Estate Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class S
Risk/Return:	rr_RiskReturnAbstract
Average Annual Return, Column Name	rr_AverageAnnualReturnColumnName	Class S Shares
Label	rr_AverageAnnualReturnLabel	Return Before Taxes
1 Year	rr_AverageAnnualReturnYear01	30.24%
5 Years	rr_AverageAnnualReturnYear05	8.19%
10 Years	rr_AverageAnnualReturnYear10	9.38%
Since Inception of Predecessor Fund	rr_AverageAnnualReturnSinceInception	6.24%
Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 28, 2007
Janus Henderson Global Real Estate Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class I
Risk/Return:	rr_RiskReturnAbstract
Average Annual Return, Column Name	rr_AverageAnnualReturnColumnName	Class I Shares
Label	rr_AverageAnnualReturnLabel	Return Before Taxes
1 Year	rr_AverageAnnualReturnYear01	30.88%
5 Years	rr_AverageAnnualReturnYear05	8.66%
10 Years	rr_AverageAnnualReturnYear10	9.85%
Since Inception of Predecessor Fund	rr_AverageAnnualReturnSinceInception	6.69%
Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 28, 2007
Janus Henderson Global Real Estate Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class N
Risk/Return:	rr_RiskReturnAbstract
Average Annual Return, Column Name	rr_AverageAnnualReturnColumnName	Class N Shares
Label	rr_AverageAnnualReturnLabel	Return Before Taxes
1 Year	rr_AverageAnnualReturnYear01	30.93%
5 Years	rr_AverageAnnualReturnYear05	8.68%
10 Years	rr_AverageAnnualReturnYear10	9.86%
Since Inception of Predecessor Fund	rr_AverageAnnualReturnSinceInception	6.69%
Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 28, 2007
Janus Henderson Global Real Estate Fund | Class A, C, S, I, N, T Shares | Return Before Taxes | Class T
Risk/Return:	rr_RiskReturnAbstract
Average Annual Return, Column Name	rr_AverageAnnualReturnColumnName	Class T Shares
Label	rr_AverageAnnualReturnLabel	Return Before Taxes
1 Year	rr_AverageAnnualReturnYear01	30.74%
5 Years	rr_AverageAnnualReturnYear05	8.49%
10 Years	rr_AverageAnnualReturnYear10	9.69%
Since Inception of Predecessor Fund	rr_AverageAnnualReturnSinceInception	6.06%
Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 28, 2007
Janus Henderson Global Real Estate Fund | Class A, C, S, I, N, T Shares | Return After Taxes on Distributions | Class I
Risk/Return:	rr_RiskReturnAbstract
Average Annual Return, Column Name	rr_AverageAnnualReturnColumnName	Class I Shares
Label	rr_AverageAnnualReturnLabel	Return After Taxes on Distributions
1 Year	rr_AverageAnnualReturnYear01	28.74%
5 Years	rr_AverageAnnualReturnYear05	6.77%
10 Years	rr_AverageAnnualReturnYear10	8.38%
Since Inception of Predecessor Fund	rr_AverageAnnualReturnSinceInception	5.36%
Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 28, 2007
Janus Henderson Global Real Estate 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
Average Annual Return, Column Name	rr_AverageAnnualReturnColumnName	Class I Shares
Label	rr_AverageAnnualReturnLabel	Return After Taxes on Distributions and Sale of Fund Shares
1 Year	rr_AverageAnnualReturnYear01	18.53%
5 Years	rr_AverageAnnualReturnYear05	5.99%
10 Years	rr_AverageAnnualReturnYear10	7.45%
Since Inception of Predecessor Fund	rr_AverageAnnualReturnSinceInception	4.83%
Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 28, 2007
Janus Henderson Global Real Estate Fund | Class A, C, S, I, N, T Shares | FTSE EPRA Nareit Global Index (reflects no deduction for expenses, fees, or taxes)
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	FTSE EPRA Nareit Global Index
1 Year	rr_AverageAnnualReturnYear01	23.58%
5 Years	rr_AverageAnnualReturnYear05	6.94%
10 Years	rr_AverageAnnualReturnYear10	8.91%
Since Inception of Predecessor Fund	rr_AverageAnnualReturnSinceInception	4.28%
Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 28, 2007
Janus Henderson Global Real Estate Fund | Class A, C, S, I, N, T Shares | FTSE EPRA Nareit Global Net Index (reflects no deduction for expenses, fees, or taxes, except foreign withholding taxes)
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	FTSE EPRA Nareit Global Net Index
1 Year	rr_AverageAnnualReturnYear01	22.50%
5 Years	rr_AverageAnnualReturnYear05	6.03%
10 Years	rr_AverageAnnualReturnYear10	8.10%
Since Inception of Predecessor Fund	rr_AverageAnnualReturnSinceInception
Inception Date	rr_AverageAnnualReturnInceptionDate	Nov. 28, 2007

[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] “Acquired Fund” refers to any underlying fund (including, but not limited to, exchange-traded funds) in which a fund invests or has invested during the period. Acquired fund fees and expenses are indirect expenses a fund may incur as a result of investing in shares of an underlying fund. To the extent that the Fund invests in Acquired Funds, the Fund’s “Total Annual Fund Operating Expenses” may not correlate to the “Ratio of gross expenses to average net assets” presented in the Financial Highlights tables because that ratio includes only the direct operating expenses incurred by the Fund, not the indirect costs of investing in Acquired Funds.

[3] 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 any performance adjustments to management fees, 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 0.91% for at least a one-year period commencing on January 28, 2020. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

[4] Calculated assuming maximum permitted sales loads.

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