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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName JANUS INVESTMENT FUND
Prospectus Date rr_ProspectusDate Oct. 26, 2012
Janus Short-Term Bond Fund | Class D Shares
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund summary

Janus Short-Term Bond Fund
Objective [Heading] rr_ObjectiveHeading INVESTMENT OBJECTIVE
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Janus Short-Term Bond Fund seeks as high a level of current income as is consistent with preservation 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.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination November 1, 2013
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 93% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 93.00%
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, 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:
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.
Strategy [Heading] rr_StrategyHeading PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock The Fund invests, under normal circumstances, at least 80% of its net assets in short- and intermediate-term securities such as corporate bonds or notes or government securities, including agency securities. The Fund may invest up to 35% of its net assets in high-yield/high risk bonds, also known as “junk bonds.” The Fund expects to maintain an average-weighted effective maturity of three years or less under normal circumstances. As of June 30, 2012, the Fund’s weighted average maturity was 2.4 years. The Fund may also invest in bank loans, mortgage-backed securities, asset-backed securities, and foreign debt securities (which may include investments in emerging markets). Due to the nature of securities in which the Fund invests, it may have relatively high portfolio turnover compared to other funds.

“Effective” maturity differs from actual maturity, which may be longer. In calculating the “effective” maturity the portfolio managers will estimate the effect of expected principal payments and call provisions on securities held in the portfolio. This gives the portfolio managers some additional flexibility in the securities they purchase, but all else being equal, could result in more volatility than if the Fund calculated an actual maturity target.

In addition, the Fund may invest its assets in derivatives, which are instruments that have a value derived from or directly linked to an underlying asset, such as equity securities, bonds, commodities, currencies, interest rates, or market indices. In particular, the Fund may use interest rate futures to manage portfolio risk. The Fund’s exposure to derivatives will vary. For purposes of meeting its 80% investment policy, the Fund may include derivatives that have characteristics similar to the Fund’s direct investments. For more information on the Fund’s use of derivatives, refer to the Fund’s shareholder reports and Form N-Q reports, which are filed with the Securities and Exchange Commission.

In addition to considering economic factors such as the effect of interest rates on the Fund’s investments, the portfolio managers apply a “bottom up” approach in choosing investments. This means that the portfolio managers look at income-producing securities one at a time to determine if a security is an attractive investment opportunity and if it is consistent with the Fund’s investment policies.
Risk [Heading] rr_RiskHeading PRINCIPAL INVESTMENT RISKS
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields will vary, and you could lose money.

Fixed-Income Securities Risk. The Fund invests in a variety of fixed-income securities. 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 the 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 the 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 the Fund would like or at the price that the portfolio managers believe the security is currently worth.

Sovereign Debt Risk. The 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.

Real Estate Risk. The Fund may be affected by risks associated with investments in real estate-related securities. The value of securities of issuers in the real estate and real estate-related industries, including real estate investment trusts, is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the issuer. These factors may impact the Fund’s investments in foreign real estate markets differently than U.S. real estate markets.

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.

Bank Loan Risk. Bank loans are obligations of companies or other entities entered into in connection with recapitalizations, acquisitions, and refinancings. The Fund’s investments in bank loans are generally acquired as a participation interest in, or assignment of, loans originated by a lender or other financial institution. These investments may include institutionally-traded floating and fixed-rate debt securities. Participation interests and assignments involve credit, interest rate, and liquidity risk. In addition, the bank loans underlying these securities often involve borrowers with low credit ratings whose financial conditions are troubled or uncertain, including companies that are highly leveraged or in bankruptcy proceedings.

Foreign Exposure Risk. The Fund may have exposure to foreign markets as a result of its investments in foreign securities, including investments in emerging markets, which can be more volatile than the U.S. markets. As a result, its returns and net asset value may be affected to a large degree by fluctuations in currency exchange rates or political or economic conditions in a particular country. In some foreign markets, there may not be protection against failure by other parties to complete transactions. It may not be possible for the Fund to repatriate capital, dividends, interest, and other income from a particular country or governmental entity. In addition, a market swing in one or more countries or regions where the Fund has invested a significant amount of its assets may have a greater effect on the Fund’s performance than it would in a more geographically diversified portfolio. To the extent the Fund invests in foreign debt securities, such investments are sensitive to changes in interest rates. Additionally, investments in securities of foreign governments involve the risk that a foreign government may not be willing or able to pay interest or repay principal when due. The Fund’s investments in emerging market countries may involve risks greater than, or in addition to, the risks of investing in more developed countries.

High-Yield/High-Risk Bond Risk. High-yield/high-risk bonds may be more sensitive than other types of bonds to economic changes, political changes, or adverse developments specific to the company that issued the bond, which may adversely affect their value.

Portfolio Turnover Risk. Increased portfolio turnover may result in higher costs, which may have a negative effect on the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

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 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 Although the Fund may be less volatile than funds that invest most of their assets in common stocks, the Fund’s returns and yields 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 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 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. The index is not actively managed and is 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/allfunds or by calling 1-800-525-3713.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.
Performance Additional Market Index [Text] rr_PerformanceAdditionalMarketIndex The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-525-3713
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress janus.com/allfunds
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 D Shares (calendar year-end)
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Best Quarter:  Second Quarter 2009  3.18%          Worst Quarter:  Second Quarter 2008  −0.90%
Year to Date Return, Label rr_YearToDateReturnLabel The Fund’s year-to-date return as of the calendar quarter ended September 30, 2012 was 3.05%.
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 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 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 the 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-deferred account, such as a 401(k) plan or an IRA.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.
Janus Short-Term Bond Fund | Class D Shares | Class D
  
Risk/Return: rr_RiskReturnAbstract  
Operating Expenses Column [Text] rr_OperatingExpensesColumnName Class D
Management Fees rr_ManagementFeesOverAssets 0.55%
Other Expenses rr_OtherExpensesOverAssets 0.19%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.74% [1]
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets 0.05% [1]
Total Annual Fund Operating Expenses After Fee Waiver rr_NetExpensesOverAssets 0.69% [1]
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class D Shares
1 Year rr_ExpenseExampleYear01 76
3 Years rr_ExpenseExampleYear03 237
5 Years rr_ExpenseExampleYear05 411
10 Years rr_ExpenseExampleYear10 918
2002 rr_AnnualReturn2002 3.57%
2003 rr_AnnualReturn2003 3.91%
2004 rr_AnnualReturn2004 1.96%
2005 rr_AnnualReturn2005 1.52%
2006 rr_AnnualReturn2006 4.21%
2007 rr_AnnualReturn2007 5.21%
2008 rr_AnnualReturn2008 4.63%
2009 rr_AnnualReturn2009 8.56%
2010 rr_AnnualReturn2010 3.48%
2011 rr_AnnualReturn2011 1.50%
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Sep. 30, 2012
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 3.05%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter:
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 3.18%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter:
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Jun. 30, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (0.90%)
Janus Short-Term Bond Fund | Class D Shares | Return Before Taxes | Class D
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class D Shares
Label rr_AverageAnnualReturnLabel Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 1.50%
5 Years rr_AverageAnnualReturnYear05 4.65%
10 Years rr_AverageAnnualReturnYear10 3.83%
Since Inception rr_AverageAnnualReturnSinceInception 4.65%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 01, 1992
Janus Short-Term Bond Fund | Class D Shares | Return After Taxes on Distributions | Class D
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class D Shares
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 0.66%
5 Years rr_AverageAnnualReturnYear05 3.43%
10 Years rr_AverageAnnualReturnYear10 2.63%
Since Inception rr_AverageAnnualReturnSinceInception 2.93%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 01, 1992
Janus Short-Term Bond Fund | Class D Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class D
  
Risk/Return: rr_RiskReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class D Shares
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions and Sale of Fund Shares [2]
1 Year rr_AverageAnnualReturnYear01 1.01%
5 Years rr_AverageAnnualReturnYear05 3.27%
10 Years rr_AverageAnnualReturnYear10 2.58%
Since Inception rr_AverageAnnualReturnSinceInception 2.90%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 01, 1992
Janus Short-Term Bond Fund | Class D Shares | Barclays 1-3 Year U.S. Government/Credit Index (reflects no deduction for expenses, fees, or taxes)
  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel Barclays 1-3 Year U.S. Government/Credit Index
1 Year rr_AverageAnnualReturnYear01 1.59%
5 Years rr_AverageAnnualReturnYear05 3.99%
10 Years rr_AverageAnnualReturnYear10 3.63%
Since Inception rr_AverageAnnualReturnSinceInception 4.80%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 01, 1992
[1] Janus Capital has contractually agreed to waive the Fund's total annual fund operating expenses (excluding administrative services fees payable pursuant to the Transfer Agency Agreement, brokerage commissions, interest, dividends, taxes, acquired fund fees and expenses, and extraordinary expenses) to 0.55% until at least November 1, 2013. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.
[2] 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.