Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	JANUS INVESTMENT FUND
Prospectus Date	rr_ProspectusDate	Jan. 26, 2018
Janus Henderson European Focus Fund | Class A, C, S, I, N, T Shares
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	FUND SUMMARY Janus Henderson European Focus Fund
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Janus Henderson European Focus Fund seeks long-term capital appreciation primarily through investment in equities of European companies.
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 European Focus Fund (the “Predecessor Fund”) and the Fund for the fiscal year August 1, 2016 to July 31, 2017 was 57% 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 6% of the average value of the portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	6.00%
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 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 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 European companies. Equity securities include common stocks and related securities, such as preferred stock, convertible securities, and depositary receipts. European companies are broadly defined to include any company that meets one or more of the following tests: (i) its country of organization, its primary business office and/or the principal trading market of its stock are located in Europe, (ii) 50% or more of its assets are located in Europe, or (iii) 50% or more of its revenues are derived from Europe. The portfolio manager seeks investments that will increase in value by emphasizing stock selection and may invest in companies of any size, including through initial public offerings and private placements. Stock selection is based on an opportunistic approach which seeks to exploit stock specific criteria described below and particular investment factors in Europe that are expected to drive stock prices. The portfolio manager will invest in both “growth” stocks that the portfolio manager believes are reasonably priced and “value” stocks that are, in the portfolio manager’s opinion, undervalued. Companies are evaluated using a broad range of criteria, including: (i) a company’s financial strength; (ii) competitive position in its industry; and (iii) projected future earnings and cash flows. The Fund has no limits on the geographic asset distribution of its investments within Europe. The Fund may invest in companies located in Western European countries such as the United Kingdom, Belgium, Germany, Norway, the Netherlands, Denmark, Switzerland, Finland, Sweden, Portugal, France, Austria, Italy and Spain. The Fund may also invest in issuers located in Central and Eastern European countries such as Russia, Bulgaria, the Czech Republic, Turkey and Poland. The Fund may, under unusual circumstances, invest in a single country or a limited number of countries. Country and sector allocation decisions are driven primarily by the stock selection process. However, in evaluating investment opportunities in various countries and sectors, the portfolio manager will consider: (i) the condition and growth potential of the various economies, industry sectors and securities markets; (ii) expected levels of inflation; (iii) government policies influencing business conditions; (iv) currency and taxation factors; and (v) other financial, social and political factors that may have an effect on the investment climate of the companies that are located in those markets. The Fund generally sells a stock when, in the portfolio manager’s opinion, there is a deterioration in the company’s fundamentals, the company fails to meet performance expectations, the stock achieves its target price, its earnings are disappointing or its revenue growth has slowed. The Fund may also sell a stock if the portfolio manager believes that negative country or regional factors may affect the company’s outlook, in the portfolio manager’s opinion, a superior investment opportunity arises or to meet cash requirements. The portfolio manager anticipates that the Fund will continue to hold securities of companies that grow or expand so long as the portfolio manager believes the securities continue to offer prospects of long-term growth. Some of the Fund’s investments may produce income, although income from dividends and interest will be incidental and not an important consideration in choosing investments. 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, commodities, or currencies, as substitutes for securities in which the Fund invests. In particular, the Fund may invest in derivatives such as forward currency contracts to offset risks associated with currency exposure. The Fund may engage in active and frequent trading to achieve its investment objective. The Fund does not limit its investments to companies of any particular size and may invest a significant portion of its assets in smaller and less seasoned issuers. However, in an attempt to reduce portfolio risks, the portfolio manager generally will invest across countries, industry groups and/or securities. The Fund may lend portfolio securities on a short-term or long-term basis, in an amount equal to up to one-third of its total assets as determined at the time of the loan origination.
Risk [Heading]	rr_RiskHeading	PRINCIPAL INVESTMENT RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio of European companies, including common stocks. Common stocks tend to be more volatile than many other investment choices. Foreign Exposure Risk.  The Fund normally has significant exposure to foreign markets as a result of its investments in foreign securities and derivatives that provide exposure to foreign markets, 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. 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. This risk increases to the extent the Fund focuses on issuers in a limited number of countries in Europe. Western Europe has, in certain instances, been susceptible to serious financial hardship, high debt levels and high levels of unemployment. The European Union itself has experienced difficulties in connection with the debt loads of some of its member states. Although Western Europe is developed, recent economic hardship will pose investment risk in neighboring emerging nations. 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. 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 manager’s belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money. Market risk may affect a single issuer, industry, economic sector, or the market as a whole. 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. 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. 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. 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 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. 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 2.8% of the Fund’s investments were in emerging markets (i.e. countries included in the MSCI Emerging Markets IndexSM). Portfolio Turnover Risk.  Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders. Growth Securities Risk.  The Fund may invest in companies that the portfolio manager believes 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 manager’s perception of a company’s growth potential is not realized, the securities purchased may not perform as expected, reducing the Fund’s returns. In addition, because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “growth” stocks may perform differently from the market as a whole and other types of securities. Value Investing Risk.  Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected by the portfolio manager. 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. Returns shown prior to June 5, 2017 are those of the Predecessor Fund, Henderson European Focus Fund. The Predecessor Fund was advised by Henderson Global Investors (North America) Inc. and subadvised by Henderson Investment Management Limited. 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 and Class C Shares of the Predecessor Fund commenced operations with the Predecessor Fund’s inception on August 31, 2001. Class I Shares and Class R6 Shares of the Predecessor Fund commenced operations on March 31, 2009 and November 30, 2015, respectively. 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, except that for periods prior to March 31, 2009, performance shown for Class I Shares reflects the performance of Class A Shares of the Predecessor Fund, calculated using the fees and expenses of Class A Shares of the Predecessor Fund (without sales charges or 12b-1 fees), 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 A Shares of the Predecessor Fund, calculated using the fees and expenses of Class A Shares of the Predecessor Fund (without sales charges or 12b-1 fees), 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 A Shares of the Predecessor Fund, calculated using the fees and expenses of Class A Shares of the Predecessor Fund (without sales charges or 12b-1 fees), 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 A Shares of the Predecessor Fund, calculated using the fees and expenses of Class A Shares of the Predecessor Fund (without sales charges or 12b-1 fees), 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 A Shares (calendar year-end)
Bar Chart Does Not Reflect Sales Loads [Text]	rr_BarChartDoesNotReflectSalesLoads	The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best Quarter:  2nd Quarter 2009  40.45%          Worst Quarter:  3rd Quarter 2008  – 32.08%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns (periods ended 12/31/17)
Performance Table Market Index Changed	rr_PerformanceTableMarketIndexChanged	Prior to June 5, 2017, the Predecessor Fund used the MSCI Europe Index gross of foreign withholding taxes. Effective June 5, 2017, the Fund’s performance will be compared to the MSCI Europe Index net of foreign withholding taxes because it more closely reflects the Fund’s investment universe and is consistent with the practices of other funds advised by Janus Capital.
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 A Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class A 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 Europe Index. The index is described below. The MSCI Europe Index is a free float-adjusted market capitalization index that is designed to measure developed market equity performance in Europe. The performance of the Index is listed in U.S. dollars and assumes reinvestment of net dividends. Prior to June 5, 2017, the Predecessor Fund used the MSCI Europe Index gross of foreign withholding taxes. Effective June 5, 2017, the Fund’s performance will be compared to the MSCI Europe Index net of foreign withholding taxes because it more closely reflects the Fund’s investment universe and is consistent with the practices of other funds advised by Janus Capital. After-tax returns are calculated using distributions for the Predecessor Fund’s Class A Shares for the period prior to June 5, 2017. If Class A 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 A Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class A 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 European Focus 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	0.94%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.16%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.35%	[2]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	0.01%	[2]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.34%	[2]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class A Shares
1 Year	rr_ExpenseExampleYear01	$ 705
3 Years	rr_ExpenseExampleYear03	978
5 Years	rr_ExpenseExampleYear05	1,272
10 Years	rr_ExpenseExampleYear10	$ 2,105
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class A Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 705
3 Years	rr_ExpenseExampleNoRedemptionYear03	978
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,272
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 2,105
2008	rr_AnnualReturn2008	(56.20%)
2009	rr_AnnualReturn2009	108.52%
2010	rr_AnnualReturn2010	18.33%
2011	rr_AnnualReturn2011	(18.88%)
2012	rr_AnnualReturn2012	23.43%
2013	rr_AnnualReturn2013	34.73%
2014	rr_AnnualReturn2014	(4.99%)
2015	rr_AnnualReturn2015	2.73%
2016	rr_AnnualReturn2016	(7.25%)
2017	rr_AnnualReturn2017	16.11%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	40.45%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(32.08%)
Janus Henderson European Focus 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	0.94%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	0.28%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.22%	[2]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	0.06%	[2]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	2.16%	[2]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class C Shares
1 Year	rr_ExpenseExampleYear01	$ 325
3 Years	rr_ExpenseExampleYear03	694
5 Years	rr_ExpenseExampleYear05	1,190
10 Years	rr_ExpenseExampleYear10	$ 2,554
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class C Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 225
3 Years	rr_ExpenseExampleNoRedemptionYear03	694
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,190
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 2,554
Janus Henderson European Focus 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	0.94%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.29%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.48%	[2]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	0.01%	[2]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.47%	[2]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class S Shares
1 Year	rr_ExpenseExampleYear01	$ 151
3 Years	rr_ExpenseExampleYear03	468
5 Years	rr_ExpenseExampleYear05	808
10 Years	rr_ExpenseExampleYear10	$ 1,768
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class S Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 151
3 Years	rr_ExpenseExampleNoRedemptionYear03	468
5 Years	rr_ExpenseExampleNoRedemptionYear05	808
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,768
Janus Henderson European Focus 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	0.94%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.12%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.06%	[2]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	none	[2]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.06%	[2]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class I Shares
1 Year	rr_ExpenseExampleYear01	$ 108
3 Years	rr_ExpenseExampleYear03	337
5 Years	rr_ExpenseExampleYear05	585
10 Years	rr_ExpenseExampleYear10	$ 1,294
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class I Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 108
3 Years	rr_ExpenseExampleNoRedemptionYear03	337
5 Years	rr_ExpenseExampleNoRedemptionYear05	585
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,294
Janus Henderson European Focus 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	0.94%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.05%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.99%	[2]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	none	[2]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	0.99%	[2]
Expenses Restated to Reflect Current [Text]	rr_ExpensesRestatedToReflectCurrent	Other Expenses for Class N Shares have been restated to reflect the estimated expenses that the Fund expects to incur.
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class N Shares
1 Year	rr_ExpenseExampleYear01	$ 101
3 Years	rr_ExpenseExampleYear03	315
5 Years	rr_ExpenseExampleYear05	547
10 Years	rr_ExpenseExampleYear10	$ 1,213
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class N Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 101
3 Years	rr_ExpenseExampleNoRedemptionYear03	315
5 Years	rr_ExpenseExampleNoRedemptionYear05	547
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,213
Janus Henderson European Focus 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	0.94%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.28%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.22%	[2]
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	0.01%	[2]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	1.21%	[2]
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class T Shares
1 Year	rr_ExpenseExampleYear01	$ 124
3 Years	rr_ExpenseExampleYear03	387
5 Years	rr_ExpenseExampleYear05	670
10 Years	rr_ExpenseExampleYear10	$ 1,477
Expense Example, No Redemption, By Year, Column [Text]	rr_ExpenseExampleNoRedemptionByYearColumnName	Class T Shares
1 Year	rr_ExpenseExampleNoRedemptionYear01	$ 124
3 Years	rr_ExpenseExampleNoRedemptionYear03	387
5 Years	rr_ExpenseExampleNoRedemptionYear05	670
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,477
Janus Henderson European Focus 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	9.45%
5 Years	rr_AverageAnnualReturnYear05	5.94%
10 Years	rr_AverageAnnualReturnYear10	3.74%
Since Inception	rr_AverageAnnualReturnSinceInception	12.94%
Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 31, 2001
Janus Henderson European Focus 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	14.26%
5 Years	rr_AverageAnnualReturnYear05	6.38%
10 Years	rr_AverageAnnualReturnYear10	3.56%
Since Inception	rr_AverageAnnualReturnSinceInception	12.49%
Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 31, 2001
Janus Henderson European Focus 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	15.97%
5 Years	rr_AverageAnnualReturnYear05	7.10%
10 Years	rr_AverageAnnualReturnYear10	4.31%
Since Inception	rr_AverageAnnualReturnSinceInception	13.31%
Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 31, 2001
Janus Henderson European Focus 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	16.42%
5 Years	rr_AverageAnnualReturnYear05	7.49%
10 Years	rr_AverageAnnualReturnYear10	4.36%
Since Inception	rr_AverageAnnualReturnSinceInception	13.35%
Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 31, 2001
Janus Henderson European Focus 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	16.32%
5 Years	rr_AverageAnnualReturnYear05	7.21%
10 Years	rr_AverageAnnualReturnYear10	4.36%
Since Inception	rr_AverageAnnualReturnSinceInception	13.35%
Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 31, 2001
Janus Henderson European Focus 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	16.11%
5 Years	rr_AverageAnnualReturnYear05	7.21%
10 Years	rr_AverageAnnualReturnYear10	4.36%
Since Inception	rr_AverageAnnualReturnSinceInception	13.35%
Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 31, 2001
Janus Henderson European Focus Fund | Class A, C, S, I, N, T Shares | Return After Taxes on Distributions | Class A
Risk/Return:	rr_RiskReturnAbstract
Column	rr_AverageAnnualReturnColumnName	Class A Shares
Label	rr_AverageAnnualReturnLabel	Return After Taxes on Distributions	[3]
1 Year	rr_AverageAnnualReturnYear01	9.25%
5 Years	rr_AverageAnnualReturnYear05	5.73%
10 Years	rr_AverageAnnualReturnYear10	3.23%
Since Inception	rr_AverageAnnualReturnSinceInception	11.93%
Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 31, 2001
Janus Henderson European Focus Fund | Class A, C, S, I, N, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class A
Risk/Return:	rr_RiskReturnAbstract
Column	rr_AverageAnnualReturnColumnName	Class A Shares
Label	rr_AverageAnnualReturnLabel	Return After Taxes on Distributions and Sale of Fund Shares	[3]
1 Year	rr_AverageAnnualReturnYear01	5.94%
5 Years	rr_AverageAnnualReturnYear05	4.75%
10 Years	rr_AverageAnnualReturnYear10	2.95%
Since Inception	rr_AverageAnnualReturnSinceInception	11.02%
Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 31, 2001
Janus Henderson European Focus Fund | Class A, C, S, I, N, T Shares | MSCI Europe Index (reflects no deduction for expenses, fees, or taxes, except foreign withholding taxes)
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	MSCI Europe Index
1 Year	rr_AverageAnnualReturnYear01	25.51%
5 Years	rr_AverageAnnualReturnYear05	7.37%
10 Years	rr_AverageAnnualReturnYear10	1.34%
Since Inception	rr_AverageAnnualReturnSinceInception	5.97%
Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 31, 2001
Janus Henderson European Focus Fund | Class A, C, S, I, N, T Shares | MSCI Europe Index (reflects no deduction for expenses, fees, or taxes)
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	MSCI Europe Index
1 Year	rr_AverageAnnualReturnYear01	26.24%
5 Years	rr_AverageAnnualReturnYear05	7.98%
10 Years	rr_AverageAnnualReturnYear10	1.96%
Since Inception	rr_AverageAnnualReturnSinceInception	6.54%
Inception Date	rr_AverageAnnualReturnInceptionDate	Aug. 31, 2001

[1] Other Expenses for Class A, Class C, Class S, Class I, and Class T Shares are based on annualized expenses from the Fund’s previous fiscal period. Other Expenses for Class N Shares 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 0.96% 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] Fund returns calculated assuming maximum permitted sales loads.

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