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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName JANUS INVESTMENT FUND
Prospectus Date rr_ProspectusDate Oct. 26, 2012
Janus Conservative Allocation Fund | Class A, C, S, I, T Shares
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund summary

Janus Conservative Allocation Fund
Objective [Heading] rr_ObjectiveHeading INVESTMENT OBJECTIVE
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Janus Conservative Allocation Fund seeks total return through a primary emphasis on income with a secondary emphasis on growth of capital.
Expense [Heading] rr_ExpenseHeading FEES AND EXPENSES OF THE FUND
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund. Each share class has different expenses, but represents an investment in the same Fund.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption SHAREHOLDER FEES
(fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover:
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 10% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 10.00%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts For Class A Shares, you may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Fund or in other Janus 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 45 of the Fund’s Prospectus and in the “Purchases” section on page 63 of the Fund’s Statement of Additional Information.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount 50,000
Expense Example [Heading] rr_ExpenseExampleHeading EXAMPLE:
Expense Example by Year [Heading] rr_ExpenseExampleByYearHeading The Example assumes that you invest $10,000 in the Fund for the time periods indicated and reinvest all dividends and distributions. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses (including the operating expenses of the underlying funds) remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption If Shares are redeemed:
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption If Shares are not redeemed:
Strategy [Heading] rr_StrategyHeading PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock The Fund seeks to achieve its investment objective by investing in other Janus mutual funds (“underlying funds”) that represent a variety of asset classes and investment styles. The Fund pursues this objective by investing in a diversified portfolio of underlying funds resulting in an allocation of the Fund’s investments that normally provides exposure of approximately 40% to stocks and 60% to bonds and money market securities. The target allocation and the allocation of the Fund’s assets among underlying funds are based on quantitative and qualitative analysis. Because it invests in other funds, the Fund is considered a “fund of funds.”

The Fund’s asset allocation is intended to diversify investments among stocks, bonds, and cash equivalents. The portfolio manager regularly reviews the allocation of Fund assets in the underlying funds and may modify the underlying funds’ weightings or substitute other underlying funds to emphasize and mitigate risk exposures that may arise as a result of the implementation of the allocations. An independent asset allocation service provides evaluations of asset allocations that the portfolio manager may use in implementing the allocations among the underlying funds. The portfolio manager continually monitors asset class allocations and periodically rebalances the Fund’s investments in the underlying funds. The portfolio manager may change the Fund’s asset class allocations, the underlying funds, an underlying fund’s asset category, or weightings among asset classes or underlying funds without prior shareholder notice.

The Fund will normally allocate approximately 60% of its investments to underlying bond funds and money market instruments; and approximately 40% of its investments to underlying funds that provide varying exposure to common stocks of large U.S.-based companies, small- to mid-capitalization companies, and international companies (including those with exposure to emerging markets). Refer to Appendix A in this Prospectus for a brief description of the investment strategies of each of the currently available underlying funds.

When market conditions dictate a more defensive strategy, the Fund or an underlying fund may temporarily hold cash or invest its assets in temporary investments. In that case, the Fund may take positions that are inconsistent with its investment objective. As a result, the Fund may not achieve its investment objective.
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 income and, to a lesser extent, growth of capital. Investments in a portfolio with common stock exposure tend to be more volatile than many other investment choices.

Main Risks Associated with the Fund
Allocation Risk. The Fund’s ability to achieve its investment objective depends largely upon the portfolio manager’s allocation of assets among the underlying funds and other securities, using the optimization process (a process that utilizes quantitative analysis of a number of factors, such as historical risk, performance, fund classifications, and the relationship among underlying funds) and the judgment of the portfolio manager. You could lose money on your investment in the Fund as a result of these allocations. The Fund will typically invest in a number of different underlying funds; however, to the extent that the Fund invests a significant portion of its assets in a single underlying fund, it will be more sensitive to the risks associated with that fund and any investments in which that fund concentrates.

Affiliated Fund Risk. Janus Capital has the authority to select and substitute underlying affiliated mutual funds. The fees paid to Janus Capital by some Janus mutual funds are generally higher than the fees paid to Janus Capital by the Fund or by other funds and share classes available for investment by the Fund. These conditions may create a conflict of interest when selecting underlying affiliated mutual funds and share classes for investment. Janus Capital, however, is a fiduciary to the Fund and its shareholders and is legally obligated to act in their best interest when selecting underlying affiliated mutual funds.

Main Risks Associated with the Underlying Funds and Securities
The biggest risk is that the underlying funds’ returns will vary, and you could lose money.

Fixed-Income Securities Risk. Approximately 60% of the Fund’s assets are allocated to fixed-income securities through investments in underlying funds. Typically, the values of fixed-income securities change inversely with prevailing interest rates. Therefore, a fundamental risk of fixed-income securities is interest rate risk, which is the risk that their value will generally decline as prevailing interest rates rise, which may cause an underlying fund’s net asset value to likewise decrease. How specific fixed-income securities may react to changes in interest rates will depend on the specific characteristics of each security. Fixed-income securities are also subject to credit risk, prepayment risk, valuation risk, and liquidity risk. Credit risk is the risk that the credit strength of an issuer of a fixed-income security will weaken and/or that the issuer will be unable to make timely principal and interest payments and that the security may go into default. Prepayment risk is the risk that during periods of falling interest rates, certain fixed-income securities with higher interest rates, such as mortgage- and asset-backed securities, may be prepaid by their issuers thereby reducing the amount of interest payments. Valuation risk is the risk that one or more of the fixed-income securities in which an underlying fund invests are priced incorrectly due to factors such as incomplete data, market instability, or human error. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that an underlying fund’s portfolio manager would like or at the price that the portfolio manager believes the security is currently worth.

Mortgage-Backed Securities Risk. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of securities. Investments in mortgage-backed securities are subject to both extension risk, where borrowers extend the duration of their mortgages in times of rising interest rates, and prepayment risk, where borrowers pay off their mortgages sooner than expected in times of declining interest rates. These risks may reduce the Fund’s returns. In addition, investments in mortgage-backed securities, including those comprised of subprime mortgages, may be subject to a higher degree of credit risk, valuation risk, and liquidity risk than various other types of fixed-income securities.

Market Risk. Approximately 40% of the Fund’s assets are allocated to equity investments through investments in underlying funds. The value of an underlying fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases or if a portfolio manager’s belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of an underlying 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.

Foreign Exposure Risk. Certain underlying funds may have significant exposure to foreign markets as a result of their investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, an underlying fund’s 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 an underlying fund has invested a significant amount of its assets may have a greater effect on an underlying fund’s performance than it would in a more geographically diversified portfolio. An underlying fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

Emerging Markets Risk. The risks of foreign investing mentioned above are heightened when investing in emerging markets. Emerging markets securities involve a number of additional risks, which may result from less government supervision and regulation of business and industry practices (including the potential lack of strict finance and accounting controls and standards), stock exchanges, brokers, and listed companies, making these investments potentially more volatile in price and less liquid than investments in developed securities markets, resulting in greater risk to investors. In addition, an underlying 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 an underlying fund’s investments. To the extent that an underlying 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 an underlying fund invests indirectly in foreign securities through various other investment vehicles including derivatives, which also involve other risks.

Sovereign Debt Risk. An underlying fund may invest in U.S. and foreign government debt securities (“sovereign debt”). Investments in U.S. sovereign debt are considered low risk. However investments in non-U.S. sovereign debt can involve a high degree of risk, including the risk that the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or to pay the interest on its sovereign debt in a timely manner.

Exchange-Traded Funds Risk. Certain underlying funds may purchase shares of exchange-traded funds (“ETFs”) to gain exposure to a particular portion of the market. ETFs are pooled investment vehicles, which may be managed or unmanaged, that generally seek to track the performance of a specific index. ETFs are traded on an exchange at market prices that may vary from the net asset value of their underlying investments. When an underlying fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF’s expenses. ETFs have certain inherent risks generally associated with investments in a portfolio of securities in which the ETF is invested, including the risk that the general level of stock prices may decline, thereby adversely affecting the value of each unit of the ETF. ETFs also involve the risk that an active trading market for an ETF’s shares may not develop or be maintained.

Exchange-Traded Notes Risk. Certain underlying funds may invest in exchange-traded notes (“ETNs”), which are debt securities whose returns are linked to a particular index. ETNs are typically linked to the performance of a commodities index that reflects the potential return on unleveraged investments in futures contracts of physical commodities, plus a specified rate of interest that could be earned on cash collateral. ETNs are subject to credit risk. The value of an ETN may vary and may be influenced by time to maturity, level of supply and demand for the ETN, volatility and lack of liquidity in underlying commodities markets, changes in the applicable interest rates, changes in the issuer’s credit rating, and economic, legal, political, or geographic events that affect the referenced commodity. When an underlying fund invests in ETNs it will bear its proportionate share of any fees and expenses borne by the ETN. There may be restrictions on an underlying fund’s right to redeem its investment in an ETN, which is meant to be held until maturity. An underlying fund’s decision to sell its ETN holdings may be limited by the availability of a secondary market.

Derivatives Risk. Certain underlying funds may invest in derivatives. 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 less liquid than other types of investments and entail the risk that the counterparty will default on its payment obligations.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Risk Lose Money [Text] rr_RiskLoseMoney The biggest risk is that the Fund’s returns will vary, and you could lose money.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading PERFORMANCE INFORMATION
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares, the initial share class) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund commenced operations on July 6, 2009.
  • 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 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 each respective share class, without the effect of any fee and expense limitations or waivers.
If Class A Shares, Class C Shares, Class S Shares, and Class I Shares of the Fund had been available during periods prior to July 6, 2009, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, and Class I 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. Performance information for each underlying fund is available in its prospectus and/or the most recent annual or semiannual report. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. 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 at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.
Performance Additional Market Index [Text] rr_PerformanceAdditionalMarketIndex The table compares the Fund’s average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-877-335-2687
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress janus.com/advisor/mutual-funds
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns for Class T Shares (calendar year-end)
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Best Quarter:  Second Quarter 2009  10.64%          Worst Quarter:  Third Quarter 2008   −6.58%
Year to Date Return, Label rr_YearToDateReturnLabel The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 9.25%.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12/31/11)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock The Conservative Allocation Index is an internally-calculated, hypothetical combination of unmanaged indices that combines total returns from the Barclays U.S. Aggregate Bond Index (60%), the Dow Jones Wilshire 5000 Index (28%), and the Morgan Stanley Capital International Europe, Australasia, Far East Index (“MSCI EAFE®”) Index (12%).

After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares, the initial share class). After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.
Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Class A
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees Column [Text] rr_ShareholderFeesColumnName Class A
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 5.75%
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther none
Operating Expenses Column [Text] rr_OperatingExpensesColumnName Class A
Management Fees rr_ManagementFeesOverAssets 0.05%
Distribution/Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.18% [1]
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.64%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.11%
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class A Shares
1 Year rr_ExpenseExampleYear01 682
3 Years rr_ExpenseExampleYear03 908
5 Years rr_ExpenseExampleYear05 1,151
10 Years rr_ExpenseExampleYear10 1,849
Expense Example, No Redemption, By Year, Column [Text] rr_ExpenseExampleNoRedemptionByYearColumnName Class A Shares
1 Year rr_ExpenseExampleNoRedemptionYear01 682
3 Years rr_ExpenseExampleNoRedemptionYear03 908
5 Years rr_ExpenseExampleNoRedemptionYear05 1,151
10 Years rr_ExpenseExampleNoRedemptionYear10 1,849
Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Class C
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees Column [Text] rr_ShareholderFeesColumnName Class C
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther 1.00%
Operating Expenses Column [Text] rr_OperatingExpensesColumnName Class C
Management Fees rr_ManagementFeesOverAssets 0.05%
Distribution/Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.20% [1]
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.64%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.89%
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class C Shares
1 Year rr_ExpenseExampleYear01 292
3 Years rr_ExpenseExampleYear03 594
5 Years rr_ExpenseExampleYear05 1,021
10 Years rr_ExpenseExampleYear10 2,212
Expense Example, No Redemption, By Year, Column [Text] rr_ExpenseExampleNoRedemptionByYearColumnName Class C Shares
1 Year rr_ExpenseExampleNoRedemptionYear01 192
3 Years rr_ExpenseExampleNoRedemptionYear03 594
5 Years rr_ExpenseExampleNoRedemptionYear05 1,021
10 Years rr_ExpenseExampleNoRedemptionYear10 2,212
Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Class S
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees Column [Text] rr_ShareholderFeesColumnName Class S
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther none
Operating Expenses Column [Text] rr_OperatingExpensesColumnName Class S
Management Fees rr_ManagementFeesOverAssets 0.05%
Distribution/Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.33% [1]
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.64%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.27%
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class S Shares
1 Year rr_ExpenseExampleYear01 129
3 Years rr_ExpenseExampleYear03 403
5 Years rr_ExpenseExampleYear05 697
10 Years rr_ExpenseExampleYear10 1,534
Expense Example, No Redemption, By Year, Column [Text] rr_ExpenseExampleNoRedemptionByYearColumnName Class S Shares
1 Year rr_ExpenseExampleNoRedemptionYear01 129
3 Years rr_ExpenseExampleNoRedemptionYear03 403
5 Years rr_ExpenseExampleNoRedemptionYear05 697
10 Years rr_ExpenseExampleNoRedemptionYear10 1,534
Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Class I
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees Column [Text] rr_ShareholderFeesColumnName Class I
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther none
Operating Expenses Column [Text] rr_OperatingExpensesColumnName Class I
Management Fees rr_ManagementFeesOverAssets 0.05%
Distribution/Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.18% [1]
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.64%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.87%
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class I Shares
1 Year rr_ExpenseExampleYear01 89
3 Years rr_ExpenseExampleYear03 278
5 Years rr_ExpenseExampleYear05 482
10 Years rr_ExpenseExampleYear10 1,073
Expense Example, No Redemption, By Year, Column [Text] rr_ExpenseExampleNoRedemptionByYearColumnName Class I Shares
1 Year rr_ExpenseExampleNoRedemptionYear01 89
3 Years rr_ExpenseExampleNoRedemptionYear03 278
5 Years rr_ExpenseExampleNoRedemptionYear05 482
10 Years rr_ExpenseExampleNoRedemptionYear10 1,073
Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Class T
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees Column [Text] rr_ShareholderFeesColumnName Class T
Maximum Sales Charge (load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (load) (as a percentage of the lower of original purchase price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther none
Operating Expenses Column [Text] rr_OperatingExpensesColumnName Class T
Management Fees rr_ManagementFeesOverAssets 0.05%
Distribution/Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.33% [1]
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.64%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.02%
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class T Shares
1 Year rr_ExpenseExampleYear01 104
3 Years rr_ExpenseExampleYear03 325
5 Years rr_ExpenseExampleYear05 563
10 Years rr_ExpenseExampleYear10 1,248
Expense Example, No Redemption, By Year, Column [Text] rr_ExpenseExampleNoRedemptionByYearColumnName Class T Shares
1 Year rr_ExpenseExampleNoRedemptionYear01 104
3 Years rr_ExpenseExampleNoRedemptionYear03 325
5 Years rr_ExpenseExampleNoRedemptionYear05 563
10 Years rr_ExpenseExampleNoRedemptionYear10 1,248
2006 rr_AnnualReturn2006 11.09%
2007 rr_AnnualReturn2007 10.19%
2008 rr_AnnualReturn2008 (16.01%)
2009 rr_AnnualReturn2009 23.37%
2010 rr_AnnualReturn2010 10.60%
2011 rr_AnnualReturn2011 1.39%
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Sep. 30, 2012
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 9.25%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter:
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 10.64%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter:
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (6.58%)
Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class A
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class A Shares
Label rr_AverageAnnualReturnLabel Return Before Taxes [2]
1 Year rr_AverageAnnualReturnYear01 (4.40%)
5 Years rr_AverageAnnualReturnYear05 3.68%
Since Inception rr_AverageAnnualReturnSinceInception 4.83%
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2005
Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class C
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class C Shares
Label rr_AverageAnnualReturnLabel Return Before Taxes [3]
1 Year rr_AverageAnnualReturnYear01 (0.28%)
5 Years rr_AverageAnnualReturnYear05 4.15%
Since Inception rr_AverageAnnualReturnSinceInception 5.10%
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2005
Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class S
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class S Shares
Label rr_AverageAnnualReturnLabel Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 1.13%
5 Years rr_AverageAnnualReturnYear05 4.63%
Since Inception rr_AverageAnnualReturnSinceInception 5.59%
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2005
Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class I
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class I Shares
Label rr_AverageAnnualReturnLabel Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 1.59%
5 Years rr_AverageAnnualReturnYear05 5.07%
Since Inception rr_AverageAnnualReturnSinceInception 6.04%
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2005
Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class T
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class T Shares
Label rr_AverageAnnualReturnLabel Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 1.39%
5 Years rr_AverageAnnualReturnYear05 5.07%
Since Inception rr_AverageAnnualReturnSinceInception 6.04%
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2005
Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Return After Taxes on Distributions | Class T
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class T Shares
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 0.44%
5 Years rr_AverageAnnualReturnYear05 3.96%
Since Inception rr_AverageAnnualReturnSinceInception 5.00%
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2005
Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class T
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class T Shares
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions and Sale of Fund Shares [4]
1 Year rr_AverageAnnualReturnYear01 0.99%
5 Years rr_AverageAnnualReturnYear05 3.73%
Since Inception rr_AverageAnnualReturnSinceInception 4.63%
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2005
Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | S&P 500 Index (reflects no deduction for expenses, fees, or taxes)
  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel S&P 500® Index
1 Year rr_AverageAnnualReturnYear01 2.11%
5 Years rr_AverageAnnualReturnYear05 (0.25%)
Since Inception rr_AverageAnnualReturnSinceInception 2.26%
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2005
Janus Conservative Allocation Fund | Class A, C, S, I, T Shares | Conservative Allocation Index (reflects no deduction for expenses, fees, or taxes)
  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel Conservative Allocation Index
1 Year rr_AverageAnnualReturnYear01 3.61%
5 Years rr_AverageAnnualReturnYear05 3.89%
Since Inception rr_AverageAnnualReturnSinceInception 4.89%
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2005
[1] Other Expenses are based on the estimated expenses that the Fund expects to incur.
[2] Calculated assuming maximum permitted sales loads.
[3] The one year return is calculated to include the contingent deferred sales charge.
[4] If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.