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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Document Type dei_DocumentType 485BPOS
Document Period End Date dei_DocumentPeriodEndDate Jul. 28, 2011
Registrant Name dei_EntityRegistrantName JANUS INVESTMENT FUND
Central Index Key dei_EntityCentralIndexKey 0000277751
Amendment Flag dei_AmendmentFlag false
Document Creation Date dei_DocumentCreationDate Jul. 28, 2011
Document Effective Date dei_DocumentEffectiveDate Jul. 29, 2011
Prospectus Date rr_ProspectusDate Jul. 29, 2011
Janus Asia Equity Fund | Class A, C, S, I, T Shares
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading FUND SUMMARY Janus Asia Equity Fund
Objective [Heading] rr_ObjectiveHeading INVESTMENT OBJECTIVE
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Janus Asia Equity Fund seeks long-term growth of capital.
FEES AND EXPENSES OF THE FUND jif277751_FundFeesAndExpensesAbstract  
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.
Expense Breakpoint Discounts jif277751_ExpenseBreakpointDiscountsAbstract  
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 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 26 of the Fund’s Prospectus and in the “Purchases” section on page 58 of the Fund’s Statement of Additional Information.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount 50,000
SHAREHOLDER FEES rr_ShareholderFeesAbstract  
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption SHAREHOLDER FEES (fees paid directly from your investment)
ANNUAL FUND OPERATING EXPENSES rr_OperatingExpensesAbstract  
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)
EXAMPLE: rr_ExpenseExampleAbstract  
Expense Example [Heading] rr_ExpenseExampleHeading EXAMPLE:
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 [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 by, Year, Caption [Text] rr_ExpenseExampleByYearCaption If Shares are redeemed:
Expense Example, No Redemption: rr_ExpenseExampleNoRedemptionAbstract  
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption If Shares are not redeemed:
Portfolio Turnover: jif277751_PortfolioTurnoverAltAbstract  
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.
Principal Investment Strategies jif277751_PrincipalInvestmentStrategiesAbstract  
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 in equity securities of Asian issuers (excluding Japanese issuers). An Asian issuer is generally considered to be any company that is (i) incorporated or has its principal business activities in an Asian country; (ii) primarily listed on the trading market of an Asian country; or (iii) derives 50% or more of its revenue from, or has 50% or more of its assets in, an Asian country. The Fund considers “Asian countries” to include, but not be limited to, Hong Kong, China, South Korea, Taiwan, Singapore, Malaysia, Thailand, Indonesia, Philippines, India, Vietnam, Pakistan, Russia, and Sri Lanka. Some of these countries may represent developing or emerging markets.

The Fund generally invests in equity securities, which consist primarily of common stocks, preferred stocks, depositary receipts, and convertible securities, but may also include other types of instruments, such as equity-linked securities and real estate investment trusts issued by Asian real estate companies. The Fund may invest in companies of any market capitalization. While the Fund intends to diversify its investments across a number of different countries, including emerging market countries, it may, under unusual circumstances, invest all or a significant portion of its assets in a single Asian country. To a more limited degree, the Fund may also invest in U.S. and foreign debt securities. Due to the nature of the securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

The portfolio manager applies a “bottom up” approach in choosing investments. In other words, the portfolio manager 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. The portfolio manager will also analyze each company from a macro perspective taking into consideration any important themes or issues that may impact the investment environment in certain regions or sectors and to estimate regional market risks.

The Fund may also invest its assets in derivatives, which are instruments that have a value derived from an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices, as substitutes for securities in which the Fund invests. The Fund intends to invest in derivatives, such as swaps, to gain access to foreign markets, in particular where direct investment may be restricted or unavailable. The Fund may also invest in derivative instruments (by taking long and/or short positions) for other purposes, including hedging, to increase or decrease the Fund’s exposure to a particular market, to manage or adjust the risk profile of the Fund related to an investment or currency exposure, and to earn income and enhance returns. The Fund’s exposure to derivatives will vary, is not limited to those derivatives listed, and could be significant at times.
Principal Investment Risks jif277751_PrincipalInvestmentRisksAbstract  
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 Asian equity portfolio, 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, including 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. A market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Emerging Markets Risk. The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities are exposed to a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. In addition, the Fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of the Fund’s investments. 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 specialized risks.

Geographic Concentration Risk. Because the Fund intends to focus its investments in a particular geographic region, the Fund’s performance is expected to be closely tied to various factors such as social, financial, economic, and political conditions within that region or country. Specifically, the Fund’s investments in Asian issuers increase the Fund’s exposure to the risks associated with volatile securities markets, adverse exchange rates, social, political and regulatory developments, and economic environmental events (such as natural disasters) which may be particular to Asian countries. Events that negatively affect the fiscal stability of Asian countries may cause the value of the Fund’s shares to decrease, in some cases significantly. As a result, the Fund is likely to be more volatile than more geographically diverse funds. In addition, many of the economies of the Asian countries in which the Fund invests are interdependent, which may cause them to experience the impact of such events at the same time or may increase the possibility that conditions in one country or region might adversely impact the issuers of securities in a different country or region.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or multiple companies 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 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.

Growth Securities Risk. Securities of companies perceived to be “growth” companies may be more volatile than other stocks and may involve special risks. The price of a “growth” security may be impacted if the company does not realize its anticipated potential or if there is a shift in the market to favor other types of securities.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations to the Fund. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance.

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.
PERFORMANCE INFORMATION jif277751_FundPastPerformanceAbstract  
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading PERFORMANCE INFORMATION
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The Fund does not have a full calendar year of operations. Performance information for certain periods will be included in the Fund’s first annual and/or semiannual report.
Performance One Year or Less [Text] rr_PerformanceOneYearOrLess The Fund does not have a full calendar year of operations.
Janus Asia Equity Fund | Class A, C, S, I, T Shares | Class A
  
SHAREHOLDER FEES rr_ShareholderFeesAbstract  
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
Redemption fee on Shares held for 90 days or less (as a percentage of amount redeemed) rr_RedemptionFeeOverRedemption none
ANNUAL FUND OPERATING EXPENSES rr_OperatingExpensesAbstract  
Operating Expenses Column [Text] rr_OperatingExpensesColumnName Class A
Management Fees (may adjust up or down) rr_ManagementFeesOverAssets 0.92%
Distribution/Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 2.73% [1]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 3.90% [2]
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets 2.32% [2]
Net Annual Fund Operating Expenses After Fee Waiver rr_NetExpensesOverAssets 1.58% [2]
EXAMPLE: rr_ExpenseExampleAbstract  
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class A Shares
1 Year rr_ExpenseExampleYear01 945
3 Years rr_ExpenseExampleYear03 1,696
Expense Example, No Redemption: rr_ExpenseExampleNoRedemptionAbstract  
Expense Example, No Redemption, By Year, Column [Text] rr_ExpenseExampleNoRedemptionByYearColumnName Class A Shares
1 Year rr_ExpenseExampleNoRedemptionYear01 945
3 Years rr_ExpenseExampleNoRedemptionYear03 1,696
Janus Asia Equity Fund | Class A, C, S, I, T Shares | Class C
  
SHAREHOLDER FEES rr_ShareholderFeesAbstract  
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%
Redemption fee on Shares held for 90 days or less (as a percentage of amount redeemed) rr_RedemptionFeeOverRedemption none
ANNUAL FUND OPERATING EXPENSES rr_OperatingExpensesAbstract  
Operating Expenses Column [Text] rr_OperatingExpensesColumnName Class C
Management Fees (may adjust up or down) rr_ManagementFeesOverAssets 0.92%
Distribution/Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 2.75% [1]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 4.67% [2]
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets 2.34% [2]
Net Annual Fund Operating Expenses After Fee Waiver rr_NetExpensesOverAssets 2.33% [2]
EXAMPLE: rr_ExpenseExampleAbstract  
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class C Shares
1 Year rr_ExpenseExampleYear01 568
3 Years rr_ExpenseExampleYear03 1,408
Expense Example, No Redemption: rr_ExpenseExampleNoRedemptionAbstract  
Expense Example, No Redemption, By Year, Column [Text] rr_ExpenseExampleNoRedemptionByYearColumnName Class C Shares
1 Year rr_ExpenseExampleNoRedemptionYear01 468
3 Years rr_ExpenseExampleNoRedemptionYear03 1,408
Janus Asia Equity Fund | Class A, C, S, I, T Shares | Class S
  
SHAREHOLDER FEES rr_ShareholderFeesAbstract  
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
Redemption fee on Shares held for 90 days or less (as a percentage of amount redeemed) rr_RedemptionFeeOverRedemption 2.00%
ANNUAL FUND OPERATING EXPENSES rr_OperatingExpensesAbstract  
Operating Expenses Column [Text] rr_OperatingExpensesColumnName Class S
Management Fees (may adjust up or down) rr_ManagementFeesOverAssets 0.92%
Distribution/Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 2.87% [1]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 4.04% [2]
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets 2.21% [2]
Net Annual Fund Operating Expenses After Fee Waiver rr_NetExpensesOverAssets 1.83% [2]
EXAMPLE: rr_ExpenseExampleAbstract  
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class S Shares
1 Year rr_ExpenseExampleYear01 406
3 Years rr_ExpenseExampleYear03 1,230
Expense Example, No Redemption: rr_ExpenseExampleNoRedemptionAbstract  
Expense Example, No Redemption, By Year, Column [Text] rr_ExpenseExampleNoRedemptionByYearColumnName Class S Shares
1 Year rr_ExpenseExampleNoRedemptionYear01 406
3 Years rr_ExpenseExampleNoRedemptionYear03 1,230
Janus Asia Equity Fund | Class A, C, S, I, T Shares | Class I
  
SHAREHOLDER FEES rr_ShareholderFeesAbstract  
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
Redemption fee on Shares held for 90 days or less (as a percentage of amount redeemed) rr_RedemptionFeeOverRedemption 2.00%
ANNUAL FUND OPERATING EXPENSES rr_OperatingExpensesAbstract  
Operating Expenses Column [Text] rr_OperatingExpensesColumnName Class I
Management Fees (may adjust up or down) rr_ManagementFeesOverAssets 0.92%
Distribution/Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 2.64% [1]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 3.56% [2]
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets 2.23% [2]
Net Annual Fund Operating Expenses After Fee Waiver rr_NetExpensesOverAssets 1.33% [2]
EXAMPLE: rr_ExpenseExampleAbstract  
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class I Shares
1 Year rr_ExpenseExampleYear01 359
3 Years rr_ExpenseExampleYear03 1,091
Expense Example, No Redemption: rr_ExpenseExampleNoRedemptionAbstract  
Expense Example, No Redemption, By Year, Column [Text] rr_ExpenseExampleNoRedemptionByYearColumnName Class I Shares
1 Year rr_ExpenseExampleNoRedemptionYear01 359
3 Years rr_ExpenseExampleNoRedemptionYear03 1,091
Janus Asia Equity Fund | Class A, C, S, I, T Shares | Class T
  
SHAREHOLDER FEES rr_ShareholderFeesAbstract  
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
Redemption fee on Shares held for 90 days or less (as a percentage of amount redeemed) rr_RedemptionFeeOverRedemption 2.00%
ANNUAL FUND OPERATING EXPENSES rr_OperatingExpensesAbstract  
Operating Expenses Column [Text] rr_OperatingExpensesColumnName Class T
Management Fees (may adjust up or down) rr_ManagementFeesOverAssets 0.92%
Distribution/Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 2.87% [1]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 3.79% [2]
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets 2.21% [2]
Net Annual Fund Operating Expenses After Fee Waiver rr_NetExpensesOverAssets 1.58% [2]
EXAMPLE: rr_ExpenseExampleAbstract  
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class T Shares
1 Year rr_ExpenseExampleYear01 381
3 Years rr_ExpenseExampleYear03 1,158
Expense Example, No Redemption: rr_ExpenseExampleNoRedemptionAbstract  
Expense Example, No Redemption, By Year, Column [Text] rr_ExpenseExampleNoRedemptionByYearColumnName Class T Shares
1 Year rr_ExpenseExampleNoRedemptionYear01 381
3 Years rr_ExpenseExampleNoRedemptionYear03 1,158
Janus Asia Equity Fund | Class D Shares
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading FUND SUMMARY Janus Asia Equity Fund
Objective [Heading] rr_ObjectiveHeading INVESTMENT OBJECTIVE
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Janus Asia Equity Fund seeks long-term growth of capital.
FEES AND EXPENSES OF THE FUND jif277751_FundFeesAndExpensesAbstract  
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.
SHAREHOLDER FEES rr_ShareholderFeesAbstract  
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption SHAREHOLDER FEES (fees paid directly from your investment)
ANNUAL FUND OPERATING EXPENSES rr_OperatingExpensesAbstract  
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)
EXAMPLE: rr_ExpenseExampleAbstract  
Expense Example [Heading] rr_ExpenseExampleHeading EXAMPLE:
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 [Heading] rr_ExpenseExampleByYearHeading The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and 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 without waivers remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Portfolio Turnover: jif277751_PortfolioTurnoverAltAbstract  
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.
Principal Investment Strategies jif277751_PrincipalInvestmentStrategiesAbstract  
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 in equity securities of Asian issuers (excluding Japanese issuers). An Asian issuer is generally considered to be any company that is (i) incorporated or has its principal business activities in an Asian country; (ii) primarily listed on the trading market of an Asian country; or (iii) derives 50% or more of its revenue from, or has 50% or more of its assets in, an Asian country. The Fund considers “Asian countries” to include, but not be limited to, Hong Kong, China, South Korea, Taiwan, Singapore, Malaysia, Thailand, Indonesia, Philippines, India, Vietnam, Pakistan, Russia, and Sri Lanka. Some of these countries may represent developing or emerging markets.

The Fund generally invests in equity securities, which consist primarily of common stocks, preferred stocks, depositary receipts, and convertible securities, but may also include other types of instruments, such as equity-linked securities and real estate investment trusts issued by Asian real estate companies. The Fund may invest in companies of any market capitalization. While the Fund intends to diversify its investments across a number of different countries, including emerging market countries, it may, under unusual circumstances, invest all or a significant portion of its assets in a single Asian country. To a more limited degree, the Fund may also invest in U.S. and foreign debt securities. Due to the nature of the securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

The portfolio manager applies a “bottom up” approach in choosing investments. In other words, the portfolio manager 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. The portfolio manager will also analyze each company from a macro perspective taking into consideration any important themes or issues that may impact the investment environment in certain regions or sectors and to estimate regional market risks.

The Fund may also invest its assets in derivatives, which are instruments that have a value derived from an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices, as substitutes for securities in which the Fund invests. The Fund intends to invest in derivatives, such as swaps, to gain access to foreign markets, in particular where direct investment may be restricted or unavailable. The Fund may also invest in derivative instruments (by taking long and/or short positions) for other purposes, including hedging, to increase or decrease the Fund’s exposure to a particular market, to manage or adjust the risk profile of the Fund related to an investment or currency exposure, and to earn income and enhance returns. The Fund’s exposure to derivatives will vary, is not limited to those derivatives listed, and could be significant at times.
Principal Investment Risks jif277751_PrincipalInvestmentRisksAbstract  
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 Asian equity portfolio, 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, including 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. A market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Emerging Markets Risk. The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities are exposed to a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. In addition, the Fund’s investments may be denominated in foreign currencies and therefore, changes in the value of a country’s currency compared to the U.S. dollar may affect the value of the Fund’s investments. 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 specialized risks.

Geographic Concentration Risk. Because the Fund intends to focus its investments in a particular geographic region, the Fund’s performance is expected to be closely tied to various factors such as social, financial, economic, and political conditions within that region or country. Specifically, the Fund’s investments in Asian issuers increase the Fund’s exposure to the risks associated with volatile securities markets, adverse exchange rates, social, political and regulatory developments, and economic environmental events (such as natural disasters) which may be particular to Asian countries. Events that negatively affect the fiscal stability of Asian countries may cause the value of the Fund’s shares to decrease, in some cases significantly. As a result, the Fund is likely to be more volatile than more geographically diverse funds. In addition, many of the economies of the Asian countries in which the Fund invests are interdependent, which may cause them to experience the impact of such events at the same time or may increase the possibility that conditions in one country or region might adversely impact the issuers of securities in a different country or region.

Market Risk. The value of the Fund’s portfolio may decrease if the value of an individual company or multiple companies 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 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.

Growth Securities Risk. Securities of companies perceived to be “growth” companies may be more volatile than other stocks and may involve special risks. The price of a “growth” security may be impacted if the company does not realize its anticipated potential or if there is a shift in the market to favor other types of securities.

Derivatives Risk. Derivatives can be highly volatile and involve risks in addition to the risks of the underlying referenced securities. Gains or losses from a derivative can be substantially greater than the derivative’s original cost, and can therefore involve leverage. Derivatives can be complex instruments and may involve analysis that differs from that required for other investment types used by the Fund. If the value of a derivative does not correlate well with the particular market or other asset class to which the derivative is intended to provide exposure, the derivative may not produce the anticipated result. Derivatives can also reduce the opportunity for gain or result in losses by offsetting positive returns in other investments. Derivatives can be less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations to the Fund. If the counterparty to a derivative transaction defaults, the Fund would risk the loss of the net amount of the payments that it contractually is entitled to receive. To the extent the Fund enters into short derivative positions, the Fund may be exposed to risks similar to those associated with short sales, including the risk that the Fund’s losses are theoretically unlimited.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance.

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.
PERFORMANCE INFORMATION jif277751_FundPastPerformanceAbstract  
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading PERFORMANCE INFORMATION
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The Fund does not have a full calendar year of operations. Performance information for certain periods will be included in the Fund’s first annual and/or semiannual report.
Performance One Year or Less [Text] rr_PerformanceOneYearOrLess The Fund does not have a full calendar year of operations.
Janus Asia Equity Fund | Class D Shares | Class D
  
SHAREHOLDER FEES rr_ShareholderFeesAbstract  
Shareholder Fees Column [Text] rr_ShareholderFeesColumnName Class D
Redemption fee on Shares held for 90 days or less (as a percentage of amount redeemed) rr_RedemptionFeeOverRedemption 2.00%
ANNUAL FUND OPERATING EXPENSES rr_OperatingExpensesAbstract  
Operating Expenses Column [Text] rr_OperatingExpensesColumnName Class D
Management Fees (may adjust up or down) rr_ManagementFeesOverAssets 0.92%
Other Expenses rr_OtherExpensesOverAssets 2.99% [1]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 3.91% [3]
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets 2.38% [3]
Net Annual Fund Operating Expenses After Fee Waiver rr_NetExpensesOverAssets 1.53% [3]
EXAMPLE: rr_ExpenseExampleAbstract  
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class D Shares
1 Year rr_ExpenseExampleYear01 393
3 Years rr_ExpenseExampleYear03 1,192
[1] Since the Fund is new, Other Expenses are based on the estimated expenses that the Fund expects to incur in its initial fiscal period. Other Expenses may include acquired fund fees and expenses (indirect expenses the Fund may incur as a result of investing in the shares of an underlying fund), which are currently estimated to be less than 0.01%. "Acquired Fund" refers to any underlying fund (including, but not limited to, exchange-traded funds) in which a fund invests or has invested during the period.
[2] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding any performance adjustments to management fees, the distribution and shareholder servicing fees - applicable to Class A Shares, Class C Shares, and Class S Shares; administrative services fees payable pursuant to the Transfer Agency Agreement - applicable to Class S Shares and Class T Shares; brokerage commissions; interest; dividends; taxes; and extraordinary expenses including, but not limited to, acquired fund fees and expenses) to 1.25% until at least February 1, 2012. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.
[3] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding any performance adjustments to management fees, administrative services fees payable pursuant to the Transfer Agency Agreement, brokerage commissions, interest, dividends, taxes, and extraordinary expenses including, but not limited to, acquired fund fees and expenses) to 1.25% until at least February 1, 2012. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.