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Risk Return Abstract rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName JANUS INVESTMENT FUND
Class D Shares | Janus Henderson Global Life Sciences 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 Global Life Sciences 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 Global Life Sciences 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.
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 34% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 34.00%
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="color:#000000;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, reinvest all dividends and </span><span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:</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.
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 companies that portfolio management believes have a life science orientation. In the Fund’s pursuit of companies with a life science orientation, the Fund has a fundamental policy to normally invest at least 25% of its total assets in securities of companies that are categorized in the “life sciences” sector, which may include companies in the following industry groups: pharmaceuticals; biotechnology; health care services; agriculture; cosmetics/personal care; and medical devices. Generally speaking, the “life sciences” relate to maintaining or improving quality of life. So, for example, companies with a “life science orientation” include companies engaged in research, development, production, or distribution of products or services related to health and personal care, medicine, or pharmaceuticals. The Fund implements its investment policies by investing primarily in equity securities of U.S. and foreign companies selected for their growth potential. The Fund normally invests in issuers from several different countries, which may include the United States. An issuer is deemed to be economically tied to a country or countries 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, the country; (ii) a majority of the issuer’s revenues are derived from one or more countries; or (iii) a majority of the issuer’s assets are located in one or more countries. The Fund may, under unusual circumstances, invest in a single country. The Fund may invest in shares of companies through initial public offerings and private placements.Portfolio management applies a “bottom up” approach in choosing investments. In other words, portfolio management looks at companies one at a time to determine if a company is an attractive investment opportunity and if it is consistent with the Fund’s investment policies. In conducting the “bottom up” analysis, portfolio management considers factors including a company’s growth potential, the strength of a company’s management, and a company’s sustainable competitive advantages, returns on investment capital, and cash flow generation. Portfolio management also applies screens, which incorporate third-party inputs, to (i) seek to avoid investing in issuers that are United Nations Global Compact violators and (ii) seek to invest at least 80% of the Fund’s net assets, under normal circumstances, in issuers with an MSCI (or an equivalent third-party data provider, as determined by portfolio management) ESG rating of BB or higher.The Fund will generally consider selling a stock when, in portfolio management’s opinion, the stock shows declining fundamentals, its competitive advantages have deteriorated, or if the stock reaches its targeted value. The Fund will also consider selling a stock if, in portfolio management’s opinion, a superior investment opportunity arises.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.
Strategy Portfolio Concentration [Text] rr_StrategyPortfolioConcentration <span style="font-family:Times New Roman;font-size:9.50pt;">In the Fund’s pursuit of companies with a life science orientation, the Fund has a fundamental policy to normally </span><span style="font-family:Times New Roman;font-size:9.50pt;">invest at least 25% of its total assets in securities of companies that are categorized in the “life sciences” sector, which may include companies in the following industry groups: pharmaceuticals; biotechnology; health care services; agriculture; cosmetics/personal care; and medical devices.</span>
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 D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares, the predecessor share class. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares, calculated using the fees and expenses in effect during the periods shown, net of any applicable fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for the periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, 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 table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index, as well as to one or more supplemental indices that have investment characteristics similar to those of the Fund. All figures assume reinvestment of dividends and distributions.The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janushenderson.com/allfunds or by calling 1-800-525-3713.
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 table compares the </span><span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">Fund’s average annual returns for the periods indicated to a broad-based securities market index, as well as to one or more supplemental indices that have investment characteristics similar to those of the Fund. 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 </span><span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">Fund’s average annual returns for the periods indicated to a broad-based securities market index, as well as to one or more supplemental indices that have investment characteristics similar to those of the Fund. 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;">1-800-525-3713</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/allfunds</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 D Shares (calendar year-end)
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Best Quarter:2nd Quarter 202021.04%Worst Quarter:1st Quarter 2020– 13.64%
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12/31/23)
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 </span><span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">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.</span>
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock The Fund’s primary benchmark index is the MSCI World Health Care Index. The Fund also compares its performance to the S&P 500 Index. The indices are described below.•The MSCI World Health Care Index is a capitalization-weighted index that measures the performance of health care stocks from developed market countries.•The S&P 500 Index is a commonly recognized, market capitalization-weighted index of 500 widely held equity securities, designed to measure broad U.S. equity performance.After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; and for the Fund’s Class J Shares, the predecessor share class, for periods prior to February 16, 2010. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. 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.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock Updated performance information is available at janushenderson.com/allfunds or by calling 1-800-525-3713.
Class D Shares | Janus Henderson Global Life Sciences 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 D Shares | Janus Henderson Global Life Sciences 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 D Shares | Janus Henderson Global Life Sciences 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 D Shares | Janus Henderson Global Life Sciences 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 D Shares | Janus Henderson Global Life Sciences 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 D Shares | Janus Henderson Global Life Sciences Fund | Industry and Sector Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock Industry and Sector Risk. The Fund 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 D Shares | Janus Henderson Global Life Sciences Fund | Life Sciences Sector Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock •Life Sciences Sector Risk. The Fund focuses its investments in securities of companies that are categorized in the “life sciences” sector, including companies in the following industry groups: pharmaceuticals, biotechnology, health care services, agriculture, cosmetic/personal care, and medical devices. Because of this, companies in the Fund’s portfolio may share common characteristics and may be more sensitive to changes in government funding or subsidies, new or anticipated legislative changes, or technological advances.
Class D Shares | Janus Henderson Global Life Sciences Fund | Initial Public Offering Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock 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. There can be no assurance that the Fund will identify favorable IPO investment opportunities.
Class D Shares | Janus Henderson Global Life Sciences Fund | ESG Investment Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock ESG Investment Risk. Because the Fund considers environmental, social, and governance (“ESG”) factors in selecting securities, the Fund may perform differently than funds that do not consider ESG factors. Due to the ESG considerations and exclusionary criteria employed by the Fund, the Fund may not be invested in certain issuers, and therefore may have lower performance than portfolios that do not apply similar criteria. ESG-related information provided by issuers and third parties, which portfolio management may utilize, continues to develop, and may be incomplete, inaccurate, use different methodologies, or be applied differently across companies and industries. Further, the regulatory landscape for ESG investing in the United States is still developing and future rules and regulations may require the Fund to modify or alter its investment process. Similarly, government policies incentivizing companies to consider their environmental or social practices may fall out of favor, which could potentially limit the Fund’s investment universe. There is also a risk that the issuers identified through the investment process employed by the Fund may fail to adhere to positive environmental or social practices, which may result in selling a security when it might otherwise be disadvantageous to do so.
Class D Shares | Janus Henderson Global Life Sciences 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 D Shares | Janus Henderson Global Life Sciences 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 D Shares | Janus Henderson Global Life Sciences 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 D Shares | Janus Henderson Global Life Sciences Fund | Private Placements Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock Private Placements Risk. Investments in private placements could decrease the Fund’s liquidity profile or prevent the Fund from disposing of such securities promptly at advantageous prices. Private placements may be less liquid than other investments because such securities may not always be readily sold in broad public markets and may have no active trading market. As a result, they may be difficult to value because market quotations may not be readily available, and the Fund might be unable to dispose of such securities promptly or at prices reflecting their true value. Transaction costs may be higher for these securities, and the Fund may get only limited information about the issuer of a private placement security, so it may be less able to anticipate a loss.
Class D Shares | Janus Henderson Global Life Sciences 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 D Shares | Janus Henderson Global Life Sciences 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 D Shares | Janus Henderson Global Life Sciences Fund | Class D  
Risk Return Abstract rr_RiskReturnAbstract  
Management Fees rr_ManagementFeesOverAssets 0.64%
Other Expenses rr_OtherExpensesOverAssets 0.16%
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
2014 rr_AnnualReturn2014 34.97%
2015 rr_AnnualReturn2015 8.32%
2016 rr_AnnualReturn2016 (12.32%)
2017 rr_AnnualReturn2017 22.59%
2018 rr_AnnualReturn2018 4.34%
2019 rr_AnnualReturn2019 29.20%
2020 rr_AnnualReturn2020 25.55%
2021 rr_AnnualReturn2021 6.82%
2022 rr_AnnualReturn2022 (2.70%)
2023 rr_AnnualReturn2023 7.50%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 21.04%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (13.64%)
Class D Shares | Janus Henderson Global Life Sciences Fund | Return Before Taxes | Class D  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 7.50%
5 Years rr_AverageAnnualReturnYear05 12.63%
10 Years rr_AverageAnnualReturnYear10 11.51%
Since Inception rr_AverageAnnualReturnSinceInception 11.30%
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 31, 1998
Class D Shares | Janus Henderson Global Life Sciences Fund | Return After Taxes on Distributions | Class D  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 6.40%
5 Years rr_AverageAnnualReturnYear05 11.05%
10 Years rr_AverageAnnualReturnYear10 9.74%
Since Inception rr_AverageAnnualReturnSinceInception 10.47%
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 31, 1998
Class D Shares | Janus Henderson Global Life Sciences Fund | Return After Taxes on Distributions and Sale of Fund Shares | Class D  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 5.15%
5 Years rr_AverageAnnualReturnYear05 9.82%
10 Years rr_AverageAnnualReturnYear10 8.95%
Since Inception rr_AverageAnnualReturnSinceInception 9.82%
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 31, 1998
Class D Shares | Janus Henderson Global Life Sciences Fund | S&P 500® Index (reflects no deduction for expenses, fees, or taxes)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 26.29%
5 Years rr_AverageAnnualReturnYear05 15.69%
10 Years rr_AverageAnnualReturnYear10 12.03%
Since Inception rr_AverageAnnualReturnSinceInception 7.56%
Class D Shares | Janus Henderson Global Life Sciences Fund | MSCI World Health Care Index (reflects no deduction for expenses, fees, or taxes, except foreign withholding taxes)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 3.76%
5 Years rr_AverageAnnualReturnYear05 10.47%
10 Years rr_AverageAnnualReturnYear10 9.01%
Since Inception rr_AverageAnnualReturnSinceInception 6.72%