Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	JANUS INVESTMENT FUND
Prospectus Date	rr_ProspectusDate	Jan. 26, 2018
Janus Henderson Global Life Sciences Fund | Class A, C, S, I, N, T Shares
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	FUND SUMMARY Janus Henderson Global Life Sciences Fund
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Janus Henderson Global Life Sciences Fund seeks long-term growth of capital.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE FUND
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	SHAREHOLDER FEES (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover:
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 38% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	38.00%
Expense Breakpoint Discounts	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 142 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
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE:
Expense Example by Year [Heading]	rr_ExpenseExampleByYearHeading	The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.
Expense Example by, Year, Caption [Text]	rr_ExpenseExampleByYearCaption	If Shares are redeemed:
Expense Example, No Redemption, By Year, Caption [Text]	rr_ExpenseExampleNoRedemptionByYearCaption	If Shares are not redeemed:
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Fund pursues its investment objective by investing, under normal circumstances, at least 80% of its net assets (plus any borrowings for investment purposes) in securities of companies that the portfolio managers believe have a life science orientation. In the Fund’s pursuit of companies with a life science orientation, the Fund has a fundamental policy to normally invest at least 25% of its total assets in securities of companies that are categorized in the “life sciences” sector, which may include companies in the following industry groups: pharmaceutical; biotechnology; health care services; and medical devices. Generally speaking, the “life sciences” relate to maintaining or improving quality of life. So, for example, companies with a “life science orientation” include companies engaged in research, development, production, or distribution of products or services related to health and personal care, medicine, or pharmaceuticals. The Fund implements its investment policies by investing primarily in equity securities of U.S. and foreign companies selected for their growth potential. The Fund normally invests in issuers from several different countries, which may include the United States. The Fund may, under unusual circumstances, invest in a single country. The Fund may have significant exposure to emerging markets. The Fund may also invest in U.S. and foreign debt securities. The Fund may invest in shares of companies through initial public offerings. The portfolio managers apply a “bottom up” approach in choosing investments. In other words, the portfolio managers look at companies one at a time to determine if a company is an attractive investment opportunity and if it is consistent with the Fund’s investment policies. The Fund may invest its assets in derivatives, which are instruments that have a value derived from, or directly linked to, an underlying asset, such as equity securities, fixed-income securities, commodities, currencies, interest rates, or market indices, as substitutes for securities in which the Fund invests. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the securities in which the Fund may directly invest. The Fund may invest in derivative instruments (by taking long and/or short positions) such as options and forward exchange contracts for different purposes, including hedging (to offset risks associated with an investment, currency exposure, or market conditions) and to earn income and enhance returns. 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	In the Fund’s pursuit of companies with a life science orientation, the Fund has a fundamental policy to normally invest at least 25% of its total assets in securities of companies that are categorized in the “life sciences” sector, which may include companies in the following industry groups: pharmaceutical; biotechnology; health care services; and medical devices.
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. Concentration Risk.  The Fund focuses its investments in securities of companies that are categorized in the “life sciences” sector, including companies in the pharmaceutical, biotechnology, health care services, and medical device industries. Because of this, companies in the Fund’s portfolio may share common characteristics and may be more sensitive to changes in government funding or subsidies, new or anticipated legislative changes, or technological advances. 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. To the extent the Fund invests in foreign debt securities, such investments are sensitive to changes in interest rates. Additionally, investments in securities of foreign governments involve the risk that a foreign government may not be willing or able to pay interest or repay principal when due. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries. Emerging Markets Risk.  The risks of foreign investing mentioned above 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. 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. Some of the risks of investing directly in foreign and emerging market securities may be reduced when the Fund invests indirectly in foreign securities through various other investment vehicles including derivatives, which also involve other risks. As of September 30, 2017, approximately 0.4% of the Fund’s investments were in emerging markets (i.e. countries included in the MSCI Emerging Markets IndexSM). 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. 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. 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. Derivatives Risk.  Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities or asset. Gains or losses from a derivative investment can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Leverage may cause the Fund to be more volatile than if it had not used leverage. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations. The Fund may use derivatives, including forward currency contracts, for hedging purposes. Hedging with derivatives may increase expenses, and there is no guarantee that a hedging strategy will work. While hedging can reduce or eliminate losses, it can also reduce or eliminate gains or cause losses if the market moves in a manner different from that anticipated by the Fund or if the cost of the derivative outweighs the benefit of the hedge. Geographic Concentration Risk.  To the extent the Fund invests a substantial amount of its assets in issuers located in a single country or region, the economic, political, regulatory or other developments or conditions within such country or region will generally have a greater effect on the Fund than they would on a more geographically diversified fund, which may result in greater losses 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. 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. Securities Lending Risk.  The Fund may seek to earn additional income through lending its securities to certain qualified broker-dealers and institutions. There is the risk that when portfolio securities are lent, the securities may not be returned on a timely basis, and the Fund may experience delays and costs in recovering the security or gaining access to the collateral provided to the Fund to collateralize the loan. If the Fund is unable to recover a security on loan, the Fund may use the collateral to purchase replacement securities in the market. There is a risk that the value of the collateral could decrease below the cost of the replacement security by the time the replacement investment is made, resulting in a loss to the Fund. Management Risk.  The Fund is an actively managed investment portfolio and is therefore subject to the risk that the investment strategies employed for the Fund may fail to produce the intended results. The Fund may underperform its benchmark index or other mutual funds with similar investment objectives. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Risk Lose Money [Text]	rr_RiskLoseMoney	The biggest risk is that the Fund’s returns will vary, and you could lose money.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	PERFORMANCE INFORMATION
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares, the initial share class) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund commenced operations on July 6, 2009. Class N Shares of the Fund commenced operations on January 26, 2018. The performance shown for Class T Shares is calculated using the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers. The performance shown for Class A Shares, Class C Shares, and Class S Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers. The performance shown for Class I Shares for periods prior to July 6, 2009, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses of Class J Shares, net of any applicable fee and expense limitations or waivers. The performance shown for Class N Shares for periods prior to December 31, 2017, reflects the performance of the Fund’s Class T Shares, calculated using the fees and expenses of Class T Shares, net of any applicable fee and expense limitations or waivers. If Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund had been available during periods prior to July 6, 2009 or Class N Shares of the Fund had been available during periods prior to December 31, 2017, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class N Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers. The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. All figures assume reinvestment of dividends and distributions. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at 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 T Shares (calendar year-end)
Bar Chart Does Not Reflect Sales Loads [Text]	rr_BarChartDoesNotReflectSalesLoads	The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best Quarter:  3rd Quarter 2013  16.48%          Worst Quarter:  4th Quarter 2008  – 18.91%
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 T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The Fund’s primary benchmark index is the MSCI World Health Care Index. The Fund also compares its performance to the S&P 500® Index. The indices are described below. The MSCI World Health Care Index is a capitalization weighted index that measures the performance of health care stocks from developed market countries in North America, Europe, and the Asia/Pacific Region. The index includes reinvestment of dividends, net of foreign withholding taxes. The S&P 500® Index is a commonly recognized, market-capitalization weighted index of 500 widely held equity securities, designed to measure broad U.S. equity performance. After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares, the initial share class). After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA. After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.
Performance Table Closing [Text Block]	rr_PerformanceTableClosingTextBlock	Updated performance information is available at janushenderson.com/performance or by calling 1-877-335-2687.
Janus Henderson Global Life Sciences 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	0.64%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.13%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.02%
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class A Shares
1 Year	rr_ExpenseExampleYear01	$ 673
3 Years	rr_ExpenseExampleYear03	881
5 Years	rr_ExpenseExampleYear05	1,106
10 Years	rr_ExpenseExampleYear10	$ 1,751
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class A Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 673
3 Years	rr_ExpenseExampleNoRedemptionYear03	881
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,106
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,751
Janus Henderson Global Life Sciences 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	0.64%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	0.16%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.80%
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class C Shares
1 Year	rr_ExpenseExampleYear01	$ 283
3 Years	rr_ExpenseExampleYear03	566
5 Years	rr_ExpenseExampleYear05	975
10 Years	rr_ExpenseExampleYear10	$ 2,116
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class C Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 183
3 Years	rr_ExpenseExampleNoRedemptionYear03	566
5 Years	rr_ExpenseExampleNoRedemptionYear05	975
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 2,116
Janus Henderson Global Life Sciences 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	0.64%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.28%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.17%
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class S Shares
1 Year	rr_ExpenseExampleYear01	$ 119
3 Years	rr_ExpenseExampleYear03	372
5 Years	rr_ExpenseExampleYear05	644
10 Years	rr_ExpenseExampleYear10	$ 1,420
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class S Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 119
3 Years	rr_ExpenseExampleNoRedemptionYear03	372
5 Years	rr_ExpenseExampleNoRedemptionYear05	644
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,420
Janus Henderson Global Life Sciences 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	0.64%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.13%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.77%
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class I Shares
1 Year	rr_ExpenseExampleYear01	$ 79
3 Years	rr_ExpenseExampleYear03	246
5 Years	rr_ExpenseExampleYear05	428
10 Years	rr_ExpenseExampleYear10	$ 954
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class I Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 79
3 Years	rr_ExpenseExampleNoRedemptionYear03	246
5 Years	rr_ExpenseExampleNoRedemptionYear05	428
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 954
Janus Henderson Global Life Sciences 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	0.64%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.04%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.68%
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class N Shares
1 Year	rr_ExpenseExampleYear01	$ 69
3 Years	rr_ExpenseExampleYear03	218
5 Years	rr_ExpenseExampleYear05	379
10 Years	rr_ExpenseExampleYear10	$ 847
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class N Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 69
3 Years	rr_ExpenseExampleNoRedemptionYear03	218
5 Years	rr_ExpenseExampleNoRedemptionYear05	379
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 847
Janus Henderson Global Life Sciences 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	0.64%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.28%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.92%
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class T Shares
1 Year	rr_ExpenseExampleYear01	$ 94
3 Years	rr_ExpenseExampleYear03	293
5 Years	rr_ExpenseExampleYear05	509
10 Years	rr_ExpenseExampleYear10	$ 1,131
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class T Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 94
3 Years	rr_ExpenseExampleNoRedemptionYear03	293
5 Years	rr_ExpenseExampleNoRedemptionYear05	509
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,131
2008	rr_AnnualReturn2008	(28.77%)
2009	rr_AnnualReturn2009	26.30%
2010	rr_AnnualReturn2010	8.13%
2011	rr_AnnualReturn2011	7.18%
2012	rr_AnnualReturn2012	24.66%
2013	rr_AnnualReturn2013	55.74%
2014	rr_AnnualReturn2014	34.83%
2015	rr_AnnualReturn2015	8.24%
2016	rr_AnnualReturn2016	(12.39%)
2017	rr_AnnualReturn2017	22.47%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2013
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	16.48%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(18.91%)
Janus Henderson Global Life Sciences 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	[2]
1 Year	rr_AverageAnnualReturnYear01	15.32%
5 Years	rr_AverageAnnualReturnYear05	17.99%
10 Years	rr_AverageAnnualReturnYear10	11.45%
Since Inception	rr_AverageAnnualReturnSinceInception	10.82%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 31, 1998
Janus Henderson Global Life Sciences 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	[3]
1 Year	rr_AverageAnnualReturnYear01	20.47%
5 Years	rr_AverageAnnualReturnYear05	18.49%
10 Years	rr_AverageAnnualReturnYear10	11.27%
Since Inception	rr_AverageAnnualReturnSinceInception	10.34%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 31, 1998
Janus Henderson Global Life Sciences 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	22.16%
5 Years	rr_AverageAnnualReturnYear05	19.23%
10 Years	rr_AverageAnnualReturnYear10	11.94%
Since Inception	rr_AverageAnnualReturnSinceInception	11.00%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 31, 1998
Janus Henderson Global Life Sciences 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	22.66%
5 Years	rr_AverageAnnualReturnYear05	19.68%
10 Years	rr_AverageAnnualReturnYear10	12.23%
Since Inception	rr_AverageAnnualReturnSinceInception	11.30%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 31, 1998
Janus Henderson Global Life Sciences 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	22.47%
5 Years	rr_AverageAnnualReturnYear05	19.52%
10 Years	rr_AverageAnnualReturnYear10	12.23%
Since Inception	rr_AverageAnnualReturnSinceInception	11.30%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 31, 1998
Janus Henderson Global Life Sciences 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	22.47%
5 Years	rr_AverageAnnualReturnYear05	19.52%
10 Years	rr_AverageAnnualReturnYear10	12.23%
Since Inception	rr_AverageAnnualReturnSinceInception	11.30%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 31, 1998
Janus Henderson Global Life Sciences Fund | Class A, C, S, I, N, T Shares | Return After Taxes on Distributions | Class T
Risk/Return:	rr_RiskReturnAbstract
Column	rr_AverageAnnualReturnColumnName	Class T Shares
Label	rr_AverageAnnualReturnLabel	Return After Taxes on Distributions
1 Year	rr_AverageAnnualReturnYear01	22.13%
5 Years	rr_AverageAnnualReturnYear05	17.68%
10 Years	rr_AverageAnnualReturnYear10	11.29%
Since Inception	rr_AverageAnnualReturnSinceInception	10.80%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 31, 1998
Janus Henderson Global Life Sciences Fund | Class A, C, S, I, N, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class T
Risk/Return:	rr_RiskReturnAbstract
Column	rr_AverageAnnualReturnColumnName	Class T Shares
Label	rr_AverageAnnualReturnLabel	Return After Taxes on Distributions and Sale of Fund Shares
1 Year	rr_AverageAnnualReturnYear01	12.99%
5 Years	rr_AverageAnnualReturnYear05	15.43%
10 Years	rr_AverageAnnualReturnYear10	9.97%
Since Inception	rr_AverageAnnualReturnSinceInception	9.79%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 31, 1998
Janus Henderson Global Life Sciences Fund | Class A, C, S, I, N, T Shares | MSCI World Health Care Index (reflects no deduction for expenses, fees, or taxes, except foreign withholding taxes)
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	MSCI World Health Care Index
1 Year	rr_AverageAnnualReturnYear01	19.80%
5 Years	rr_AverageAnnualReturnYear05	13.88%
10 Years	rr_AverageAnnualReturnYear10	8.94%
Since Inception	rr_AverageAnnualReturnSinceInception	5.98%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 31, 1998
Janus Henderson Global Life Sciences Fund | Class A, C, S, I, N, T Shares | S&P 500® Index (reflects no deduction for expenses, fees, or taxes)
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	S&P 500® Index
1 Year	rr_AverageAnnualReturnYear01	21.83%
5 Years	rr_AverageAnnualReturnYear05	15.79%
10 Years	rr_AverageAnnualReturnYear10	8.50%
Since Inception	rr_AverageAnnualReturnSinceInception	6.17%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 31, 1998

[1] Other Expenses for Class N Shares are based on the estimated annualized expenses that the Shares expect to incur.

[2] Calculated assuming maximum permitted sales loads.

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