Label	Element	Value
Risk Return Abstract	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	JANUS INVESTMENT FUND
Class A C S I N R T Shares | Janus Henderson Overseas Fund
Risk Return Abstract	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	<span style="color:#000000;font-family:Times New Roman;font-size:15.20pt;font-weight:bold;margin-left:3pt;">Janus Henderson Overseas Fund</span>
Objective [Heading]	rr_ObjectiveHeading	<span style="color:#FFFFFF;font-family:Times New Roman;font-size:10.45pt;font-weight:bold;margin-left:0.0pt;text-transform:uppercase;">Investment Objective</span>
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Janus Henderson Overseas Fund seeks long-term growth of capital.
Expense [Heading]	rr_ExpenseHeading	<span style="color:#FFFFFF;font-family:Times New Roman;font-size:10.45pt;font-weight:bold;margin-left:0.0pt;text-transform:uppercase;">Fees and Expenses of the Fund</span>
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy, hold, and sell Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund. For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus Henderson 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 128 of the Fund’s Prospectus and in the “Purchases” section on page 77 of the Fund’s Statement of Additional Information. In addition, please see Appendix A – Intermediary Sales Charge Waivers and Discounts. You may also incur brokerage commissions charged by your broker or financial intermediary when buying Class I Shares or Class N Shares of the Fund that are not reflected in the table or in the example below.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	SHAREHOLDER FEES (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	<span style="font-family:Times New Roman;font-size:9.50pt;font-weight:bold;">Portfolio Turnover:</span>
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 42% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	42.00%
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	<span style="font-family:Times New Roman;font-size:9.50pt;">For Class A Shares, you may qualify for sales charge </span><span style="font-family:Times New Roman;font-size:9.50pt;">discounts if you and your family invest, or agree to invest in the future, at least </span><span style="font-family:Times New Roman;font-size:9.50pt;">$50,000</span><span style="font-family:Times New Roman;font-size:9.50pt;"> in the Fund or in other Janus Henderson 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 128 of the Fund’s Prospectus and in the “Purchases” section on page 77 of the Fund’s Statement of Additional Information. In addition, please see Appendix A – Intermediary Sales Charge Waivers and Discounts. You may also incur brokerage commissions charged by your broker or financial intermediary when buying Class I Shares or Class N Shares of the Fund that are not reflected in the table or in the example below.</span>
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	$ 50,000
Expense Example [Heading]	rr_ExpenseExampleHeading	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;font-weight:bold;">EXAMPLE:</span>
Expense Example by Year [Heading]	rr_ExpenseExampleByYearHeading	<span style="font-family:Times New Roman;font-size:9.50pt;">The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends </span><span style="font-family:Times New Roman;font-size:9.50pt;">and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Class C Shares automatically convert to Class A Shares after eight years. The Example for Class C Shares for the ten-year period reflects the conversion to Class A Shares. Although your actual costs may be higher or lower, based on these assumptions your costs would be:</span>
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.
Expense Example by, Year, Caption [Text]	rr_ExpenseExampleByYearCaption	If Shares are redeemed
Expense Example, No Redemption, By Year, Caption [Text]	rr_ExpenseExampleNoRedemptionByYearCaption	If Shares are not redeemed
Strategy [Heading]	rr_StrategyHeading	<span style="color:#FFFFFF;font-family:Times New Roman;font-size:10.45pt;font-weight:bold;margin-left:0.0pt;text-transform:uppercase;">Principal investment strategies</span>
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 issuers or companies from countries outside of the United States. The Fund normally invests in a portfolio of 30-50 securities of issuers from several different countries, excluding the United States, and it may, under unusual circumstances, invest all or substantially all of its assets in a single country. The Fund may invest up to 20% of its net assets, measured at the time of purchase, in U.S. issuers. An issuer is deemed to be from a country or countries outside of the United States if one or more of the following tests are met: (i) the issuer is organized in, or its primary business office or principal trading market of its equity is located in, a country outside of the United States; (ii) a majority of the issuer’s revenues are derived from outside of the United States; or (iii) a majority of the issuer’s assets are located outside of the United States. The Fund may have significant exposure to emerging markets. The Fund typically invests in equity securities (such as stocks or any other security representing an ownership interest) in all market capitalizations.Portfolio management applies a “bottom up” approach in choosing investments. In other words, portfolio management looksat 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. Portfolio management will generally consider selling a security when, among other things, the security no longer reflects portfolio management’s investment thesis, the security approaches or exceeds its targeted value, there has been a change in a security’s risk/reward potential, or a better idea is identified.The Fund may invest in equity and debt securities of real estate-related companies. These securities may include common stocks, preferred stocks, and other securities, including, but not limited to, real estate-backed securities, securities of real estate investment trusts (“REITs”) and similar REIT-like entities.The Fund may take long or short positions in derivatives. Derivatives are instruments that have a value derived from, or directly linked to, an underlying asset, such as equity securities, commodities, currencies, interest rates, or market indices. 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 types of derivatives in which the Fund may invest include options, futures, swaps, warrants, and forward currency contracts. The Fund may use derivatives to hedge, to earn income or enhance returns, as a substitute for securities in which the Fund invests, to increase or decrease the Fund’s exposure to a particular market, to adjust the Fund’s currency exposure relative to its benchmark index, to gain access to foreign markets where direct investment may be restricted or unavailable, or to manage the Fund’s risk profile.The Fund may seek to earn additional income through lending its securities to certain qualified broker-dealers and institutions on a short-term or long-term basis, in an amount equal to up to one-third of its total assets as determined at the time of the loan origination.
Risk [Heading]	rr_RiskHeading	<span style="color:#FFFFFF;font-family:Times New Roman;font-size:10.45pt;font-weight:bold;margin-left:0.0pt;text-transform:uppercase;">Principal investment risks</span>
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	<span style="color:#FFFFFF;font-family:Times New Roman;font-size:10.45pt;font-weight:bold;margin-left:0.0pt;text-transform:uppercase;">Performance information</span>
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class 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, Class I Shares, and Class R Shares of the Fund commenced operations on July 6, 2009. Class N Shares of the Fund commenced operations on May 31, 2012.•The performance shown for Class 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, Class S Shares, and Class R 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 May 31, 2012, 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, Class I Shares, and Class R 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 May 31, 2012, the performance shown for each respective share class may have been different. The performance shown for the periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, Class I Shares, Class N Shares, and Class R Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. 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 atjanushenderson.com/performance or by calling 1-877-335-2687.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">The bar chart depicts the change in performance from year to year during the periods indicated. </span><span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">The bar chart figures do not </span><span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.</span><span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">The table compares the Fund’s average annual returns for </span><span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">the periods indicated to a broad-based securities market index. All figures assume reinvestment of dividends and distributions.</span>
Performance Additional Market Index [Text]	rr_PerformanceAdditionalMarketIndex	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">The table compares the Fund’s average annual returns for </span><span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">the periods indicated to a broad-based securities market index. All figures assume reinvestment of dividends and distributions.</span>
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;font-style:italic;">1-877-335-2687</span>
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;font-style:italic;">janushenderson.com/performance</span>
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;font-style:italic;">The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.</span>
Bar Chart [Heading]	rr_BarChartHeading	Annual Total Returns for Class T Shares (calendar year-end)
Bar Chart Does Not Reflect Sales Loads [Text]	rr_BarChartDoesNotReflectSalesLoads	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">The bar chart figures do not </span><span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.</span>
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best Quarter:4th Quarter 202021.09%Worst Quarter:1st Quarter 2020– 24.83%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns (periods ended 12/31/23)
Performance Table Does Reflect Sales Loads	rr_PerformanceTableDoesReflectSalesLoads	<span style="color:#000000;font-family:Times New Roman;font-size:7.60pt;">The one year return is calculated to include the contingent deferred sales charge.</span>
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. </span>
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">Actual after-tax returns depend on your individual tax situation and may differ </span><span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-advantaged account, such as a 401(k) plan or an IRA.</span>
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">After-tax returns are only shown for Class 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.</span>
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The Fund’s primary benchmark index is the MSCI All Country World ex-USA Index. The index is described below.•The MSCI All Country World ex-USA Index is designed to measure equity market performance in global developed and emerging markets outside the United States.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-advantaged 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 atjanushenderson.com/performance or by calling 1-877-335-2687.
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Risk Lose Money [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	The biggest risk is that the Fund’s returns will vary, and you could lose money.
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Risk Not Insured Depository Institution [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	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.
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Market Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Market Risk. The value of the Fund’s portfolio may decrease due to short-term market movements and over more prolonged market downturns. As a result, the Fund’s net asset value may fluctuate and it may be more difficult to value or sell the Fund’s holdings. Market risk may affect a single issuer, industry, economic sector, or the market as a whole. Market risk may be magnified if certain social, political, economic, and other conditions and events (such as terrorism, conflicts, including related sanctions, social unrest, natural disasters, epidemics and pandemics, including COVID-19) adversely interrupt the global economy and financial markets. 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.
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Foreign Exposure Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Foreign Exposure Risk. Foreign markets can be more volatile than the U.S. market. As a result, the Fund’s returns and net asset value may be affected by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio.
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Currency Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Currency Risk. Currency risk is the risk that changes in the exchange rate between currencies will adversely affect the value (in U.S. dollar terms) of an investment. As long as the Fund holds a foreign security, its value will be affected by the value of the local currency relative to the U.S. dollar. When the Fund sells a foreign currency denominated security, its value may be worth less in U.S. dollars even if the security increases in value in its home country. U.S. dollar-denominated securities of foreign issuers may also be affected by currency risk, as the value of these securities may also be affected by changes in the issuer’s local currency.
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Emerging Markets Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Emerging Markets Risk. Emerging market securities involve a number of 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. Information about emerging market companies, including financial information, may be less available or reliable and the Adviser’s ability to conduct due diligence with respect to such companies may be limited. Accordingly, these investments may be 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 current or 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 taxation systems at the federal, regional, and local levels in developing or emerging market countries may be less transparent, inconsistently enforced, and subject to change. Emerging markets may be subject to a higher degree of corruption and fraud than developed markets,and financial institutions and transaction counterparties may have less financial sophistication, creditworthiness, and/or resources than participants in developed markets.
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Industry and Sector Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Industry and Sector Risk. Although the Fund does not concentrate its investments in specific industries, it may have a significant portion of its assets invested in securities of companies conducting similar business or businesses within the same economic sector. Companies in the same industry or economic sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments than funds that invest more broadly. As the Fund’s portfolio becomes more concentrated, the Fund is less able to spread risk and potentially reduce the risk of loss and volatility. In addition, the Fund may be overweight or underweight in certain industries or sectors relative to its benchmark index, which may cause the Fund’s performance to be more or less sensitive to developments affecting those sectors.
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Portfolio Management Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Portfolio Management Risk. The Fund is an actively managed investment portfolio and is therefore subject to the risk that the investment strategies and research process employed for the Fund may fail to produce the intended results. Accordingly,the Fund may underperform its benchmark index or other mutual funds with similar investment objectives.
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Issuer Concentration Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Issuer Concentration Risk. The Fund’s portfolio may be comprised of a relatively small number of issuers in comparison to other funds. As a result, the Fund may be subject to greater risks than a fund that invests in a greater number of issuers. A change in the value of any single investment held by the Fund may affect the overall value of the Fund more than it would affect a fund that holds more investments. In particular, the Fund may be more susceptible to adverse developments affecting any single issuer held by the Fund and may be susceptible to greater losses because of these developments.
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Geographic Concentration Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	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, social, 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. Adverse developments in certain regions could also adversely affect securities of other countries whose economies appear to be unrelated and could have a negative impact on the Fund’s performance.
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Europe Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	•Europe Risk. The Fund is subject to certain risks related to Europe. Investments in British companies may subject the Fund to social, regulatory, political, currency, security, and economic risk specific to the United Kingdom. The United Kingdom has one of the largest economies in Europe, and the United States and other European countries are substantial trading partners of the United Kingdom. As a result, the British economy may be impacted by changes to the economic health of the United States and other European countries. 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. The markets in Eastern Europe remain relatively undeveloped and can be particularly sensitive to political and economic developments.
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Small- and Mid-Sized Companies Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Small- and Mid-Sized Companies Risk. 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, small- and mid-sized companies may 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.
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Growth Securities Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Growth Securities Risk. Securities of companies perceived to be “growth” companies may be more volatile than other stocks and may involve special risks. If portfolio management’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 other types of securities and the market as a whole.
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Value Investing Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	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 portfolio management.
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Derivatives Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Derivatives Risk. Derivatives can be 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 entail the risk that the counterparty will default on its payment obligations. Derivatives used for hedging purposes may reduce or eliminate gains or cause losses if the market moves in a manner different from that anticipated by portfolio management or if the cost of the derivative outweighs the benefit of the hedge.
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Liquidity Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Liquidity Risk. The Fund may invest in securities or instruments that do not trade actively or in large volumes, and may make investments that are less liquid than other investments. Also, the Fund may make investments that may become less liquid in response to market developments or adverse investor perceptions. Investments that are illiquid or that trade in lower volumes may be more difficult to value. When there is no willing buyer and investments cannot be readily sold at the desired time or price, the Fund may have to accept a lower price or may not be able to sell the security or instrument at all. Investments in foreign securities, particularly those of issuers located in emerging market countries, tend to have greater exposure to liquidity risk than domestic securities. In unusual market conditions, even normally liquid securities may be affected by a degree of liquidity risk (i.e., if the number and capacity of traditional market participants is reduced). An inability to sell one or more portfolio positions can adversely affect the Fund’s value or prevent the Fund from being able to take advantage of other investment opportunities.
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Securities Lending Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	Securities Lending Risk. 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.
Class A C S I N R T Shares | Janus Henderson Overseas Fund | REIT Risk [Member]
Risk Return Abstract	rr_RiskReturnAbstract
Risk [Text Block]	rr_RiskTextBlock	REIT Risk. REITs are subject to certain risks inherent in the direct ownership of real estate, including without limitation, a possible lack of mortgage funds and associated interest rate risks, overbuilding, property vacancies, increases in property taxes and operating expenses, changes in zoning laws, losses due to environmental damages and changes in neighborhood values and appeal to purchasers. In addition, a REIT could fail to qualify for tax-free pass-through of its income under the Internal Revenue Code of 1986, as amended, 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. Dividends received by the Fund from a REIT generally will not constitute qualified dividend income.
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Class A
Risk Return Abstract	rr_RiskReturnAbstract
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	5.75%
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Management Fees	rr_ManagementFeesOverAssets	0.74%	[1]
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.21%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.20%
1 Year	rr_ExpenseExampleYear01	$ 690
3 Years	rr_ExpenseExampleYear03	934
5 Years	rr_ExpenseExampleYear05	1,197
10 Years	rr_ExpenseExampleYear10	1,946
1 Year	rr_ExpenseExampleNoRedemptionYear01	690
3 Years	rr_ExpenseExampleNoRedemptionYear03	934
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,197
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,946
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Class C
Risk Return Abstract	rr_RiskReturnAbstract
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	1.00%
Management Fees	rr_ManagementFeesOverAssets	0.74%	[1]
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	0.20%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.94%
1 Year	rr_ExpenseExampleYear01	$ 297
3 Years	rr_ExpenseExampleYear03	609
5 Years	rr_ExpenseExampleYear05	1,047
10 Years	rr_ExpenseExampleYear10	2,072
1 Year	rr_ExpenseExampleNoRedemptionYear01	197
3 Years	rr_ExpenseExampleNoRedemptionYear03	609
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,047
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 2,072
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Class S
Risk Return Abstract	rr_RiskReturnAbstract
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Management Fees	rr_ManagementFeesOverAssets	0.74%	[1]
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.30%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.29%
1 Year	rr_ExpenseExampleYear01	$ 131
3 Years	rr_ExpenseExampleYear03	409
5 Years	rr_ExpenseExampleYear05	708
10 Years	rr_ExpenseExampleYear10	1,556
1 Year	rr_ExpenseExampleNoRedemptionYear01	131
3 Years	rr_ExpenseExampleNoRedemptionYear03	409
5 Years	rr_ExpenseExampleNoRedemptionYear05	708
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,556
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Class I
Risk Return Abstract	rr_RiskReturnAbstract
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Management Fees	rr_ManagementFeesOverAssets	0.74%	[1]
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.17%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.91%
1 Year	rr_ExpenseExampleYear01	$ 93
3 Years	rr_ExpenseExampleYear03	290
5 Years	rr_ExpenseExampleYear05	504
10 Years	rr_ExpenseExampleYear10	1,120
1 Year	rr_ExpenseExampleNoRedemptionYear01	93
3 Years	rr_ExpenseExampleNoRedemptionYear03	290
5 Years	rr_ExpenseExampleNoRedemptionYear05	504
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,120
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Class N
Risk Return Abstract	rr_RiskReturnAbstract
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Management Fees	rr_ManagementFeesOverAssets	0.74%	[1]
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.06%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.80%
1 Year	rr_ExpenseExampleYear01	$ 82
3 Years	rr_ExpenseExampleYear03	255
5 Years	rr_ExpenseExampleYear05	444
10 Years	rr_ExpenseExampleYear10	990
1 Year	rr_ExpenseExampleNoRedemptionYear01	82
3 Years	rr_ExpenseExampleNoRedemptionYear03	255
5 Years	rr_ExpenseExampleNoRedemptionYear05	444
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 990
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Class R
Risk Return Abstract	rr_RiskReturnAbstract
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Management Fees	rr_ManagementFeesOverAssets	0.74%	[1]
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.50%
Other Expenses	rr_OtherExpensesOverAssets	0.32%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.56%
1 Year	rr_ExpenseExampleYear01	$ 159
3 Years	rr_ExpenseExampleYear03	493
5 Years	rr_ExpenseExampleYear05	850
10 Years	rr_ExpenseExampleYear10	1,856
1 Year	rr_ExpenseExampleNoRedemptionYear01	159
3 Years	rr_ExpenseExampleNoRedemptionYear03	493
5 Years	rr_ExpenseExampleNoRedemptionYear05	850
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,856
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Class T
Risk Return Abstract	rr_RiskReturnAbstract
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds)	rr_MaximumDeferredSalesChargeOverOther	none
Management Fees	rr_ManagementFeesOverAssets	0.74%	[1]
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.30%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.04%
1 Year	rr_ExpenseExampleYear01	$ 106
3 Years	rr_ExpenseExampleYear03	331
5 Years	rr_ExpenseExampleYear05	574
10 Years	rr_ExpenseExampleYear10	1,271
1 Year	rr_ExpenseExampleNoRedemptionYear01	106
3 Years	rr_ExpenseExampleNoRedemptionYear03	331
5 Years	rr_ExpenseExampleNoRedemptionYear05	574
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,271
2014	rr_AnnualReturn2014	(13.72%)
2015	rr_AnnualReturn2015	(8.55%)
2016	rr_AnnualReturn2016	(6.91%)
2017	rr_AnnualReturn2017	31.17%
2018	rr_AnnualReturn2018	(15.36%)
2019	rr_AnnualReturn2019	27.01%
2020	rr_AnnualReturn2020	16.58%
2021	rr_AnnualReturn2021	13.04%
2022	rr_AnnualReturn2022	(8.82%)
2023	rr_AnnualReturn2023	10.81%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Dec. 31, 2020
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	21.09%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Mar. 31, 2020
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(24.83%)
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Return Before Taxes | Class A
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	4.25%	[2]
5 Years	rr_AverageAnnualReturnYear05	9.57%	[2]
10 Years	rr_AverageAnnualReturnYear10	2.45%	[2]
Since Inception	rr_AverageAnnualReturnSinceInception	7.37%	[2]
Inception Date	rr_AverageAnnualReturnInceptionDate	May 02, 1994	[2]
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Return Before Taxes | Class C
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	8.93%	[3]
5 Years	rr_AverageAnnualReturnYear05	9.99%	[3]
10 Years	rr_AverageAnnualReturnYear10	2.26%	[3]
Since Inception	rr_AverageAnnualReturnSinceInception	6.83%	[3]
Inception Date	rr_AverageAnnualReturnInceptionDate	May 02, 1994	[3]
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Return Before Taxes | Class S
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	10.52%
5 Years	rr_AverageAnnualReturnYear05	10.79%
10 Years	rr_AverageAnnualReturnYear10	3.00%
Since Inception	rr_AverageAnnualReturnSinceInception	7.46%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 02, 1994
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Return Before Taxes | Class I
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	10.94%
5 Years	rr_AverageAnnualReturnYear05	11.23%
10 Years	rr_AverageAnnualReturnYear10	3.40%
Since Inception	rr_AverageAnnualReturnSinceInception	7.80%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 02, 1994
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Return Before Taxes | Class N
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	11.06%
5 Years	rr_AverageAnnualReturnYear05	11.34%
10 Years	rr_AverageAnnualReturnYear10	3.50%
Since Inception	rr_AverageAnnualReturnSinceInception	7.83%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 02, 1994
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Return Before Taxes | Class R
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	10.26%
5 Years	rr_AverageAnnualReturnYear05	10.52%
10 Years	rr_AverageAnnualReturnYear10	2.74%
Since Inception	rr_AverageAnnualReturnSinceInception	7.21%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 02, 1994
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Return Before Taxes | Class T
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	10.81%
5 Years	rr_AverageAnnualReturnYear05	11.08%
10 Years	rr_AverageAnnualReturnYear10	3.27%
Since Inception	rr_AverageAnnualReturnSinceInception	7.73%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 02, 1994
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Return After Taxes on Distributions | Class T
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	10.64%
5 Years	rr_AverageAnnualReturnYear05	10.92%
10 Years	rr_AverageAnnualReturnYear10	3.02%
Since Inception	rr_AverageAnnualReturnSinceInception	7.20%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 02, 1994
Class A C S I N R T Shares | Janus Henderson Overseas Fund | Return After Taxes on Distributions and Sale of Fund Shares | Class T
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	6.81%
5 Years	rr_AverageAnnualReturnYear05	8.98%
10 Years	rr_AverageAnnualReturnYear10	2.62%
Since Inception	rr_AverageAnnualReturnSinceInception	6.71%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 02, 1994
Class A C S I N R T Shares | Janus Henderson Overseas Fund | MSCI All Country World ex-USA Index (reflects no deduction for expenses, fees, or taxes, except foreign withholding taxes) | Class A
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	15.62%
5 Years	rr_AverageAnnualReturnYear05	7.08%
10 Years	rr_AverageAnnualReturnYear10	3.83%
Since Inception	rr_AverageAnnualReturnSinceInception
Class A C S I N R T Shares | Janus Henderson Overseas Fund | MSCI All Country World ex-USA Index (reflects no deduction for expenses, fees, or taxes, except foreign withholding taxes) | Class C
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	15.62%
5 Years	rr_AverageAnnualReturnYear05	7.08%
10 Years	rr_AverageAnnualReturnYear10	3.83%
Since Inception	rr_AverageAnnualReturnSinceInception
Class A C S I N R T Shares | Janus Henderson Overseas Fund | MSCI All Country World ex-USA Index (reflects no deduction for expenses, fees, or taxes, except foreign withholding taxes) | Class S
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	15.62%
5 Years	rr_AverageAnnualReturnYear05	7.08%
10 Years	rr_AverageAnnualReturnYear10	3.83%
Since Inception	rr_AverageAnnualReturnSinceInception
Class A C S I N R T Shares | Janus Henderson Overseas Fund | MSCI All Country World ex-USA Index (reflects no deduction for expenses, fees, or taxes, except foreign withholding taxes) | Class I
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	15.62%
5 Years	rr_AverageAnnualReturnYear05	7.08%
10 Years	rr_AverageAnnualReturnYear10	3.83%
Since Inception	rr_AverageAnnualReturnSinceInception
Class A C S I N R T Shares | Janus Henderson Overseas Fund | MSCI All Country World ex-USA Index (reflects no deduction for expenses, fees, or taxes, except foreign withholding taxes) | Class N
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	15.62%
5 Years	rr_AverageAnnualReturnYear05	7.08%
10 Years	rr_AverageAnnualReturnYear10	3.83%
Since Inception	rr_AverageAnnualReturnSinceInception
Class A C S I N R T Shares | Janus Henderson Overseas Fund | MSCI All Country World ex-USA Index (reflects no deduction for expenses, fees, or taxes, except foreign withholding taxes) | Class R
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	15.62%
5 Years	rr_AverageAnnualReturnYear05	7.08%
10 Years	rr_AverageAnnualReturnYear10	3.83%
Since Inception	rr_AverageAnnualReturnSinceInception
Class A C S I N R T Shares | Janus Henderson Overseas Fund | MSCI All Country World ex-USA Index (reflects no deduction for expenses, fees, or taxes, except foreign withholding taxes) | Class T
Risk Return Abstract	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	15.62%
5 Years	rr_AverageAnnualReturnYear05	7.08%
10 Years	rr_AverageAnnualReturnYear10	3.83%
Since Inception	rr_AverageAnnualReturnSinceInception

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

[2] Calculated assuming maximum permitted sales loads.

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