Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	JANUS INVESTMENT FUND
Prospectus Date	rr_ProspectusDate	Jan. 28, 2015
Janus Balanced Fund | Class D Shares
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	FUND SUMMARY Janus Balanced Fund
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Janus Balanced Fund seeks long-term capital growth, consistent with preservation of capital and balanced by current income.
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)
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 72% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	72.00%
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 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.
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Fund pursues its investment objective by normally investing 35-65% of its assets in equity securities and the remaining assets in fixed-income securities and cash equivalents. The Fund normally invests at least 25% of its assets in fixed-income senior securities. The Fund’s fixed-income investments may reflect a broad range of credit qualities and may include corporate debt securities, U.S. Government obligations, mortgage-backed securities and other mortgage-related products, and short-term securities. The Fund will limit its investment in high-yield/high-risk bonds, also known as “junk” bonds, to 35% or less of its net assets. The Fund may also invest in foreign securities, which may include investments in emerging markets. As of September 30, 2014, approximately 56.4% of the Fund’s assets were held in equity securities. In choosing investments for the Fund, the portfolio managers apply a “bottom up” approach with one portfolio manager focusing on the equity portion of the Fund and the other portfolio manager focusing on the fixed-income portion of the Fund. With respect to corporate issuers, the portfolio managers look 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 managers may also consider economic factors, such as the effect of interest rates on certain of the Fund’s fixed-income investments. The portfolio managers share day-to-day responsibility for the Fund’s investments.
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 a balanced portfolio, including common stocks and bonds. Common stocks tend to be more volatile than many other investment choices. Market Risk. The value of the 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 the portfolio managers’ belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities 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. Market risk may affect a single issuer, industry, economic sector, or the market as a whole. Growth Securities Risk. The Fund invests in companies after assessing their growth potential. Securities of companies perceived to be “growth” companies may be more volatile than other stocks and may involve special risks. If the portfolio managers’ perception of a company’s growth potential is not realized, the securities purchased may not perform as expected, reducing the Fund’s returns. In addition, because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “growth” stocks may perform differently from the market as a whole and other types of securities. Fixed-Income Securities Risk. The Fund may hold debt and other fixed-income securities to generate income. 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 the value of such securities will generally decline as prevailing interest rates rise, which may cause the Fund’s net asset value to likewise decrease. The Fund may be subject to heightened interest rate risk because the Federal Reserve has ended its monetary stimulus program known as quantitative easing. The conclusion of quantitative easing and/or rising interest rates may expose fixed-income markets to increased volatility, which could cause the Fund’s net asset value to fluctuate more. If rising interest rates cause the Fund to lose enough value, the Fund could also face increased shareholder redemptions, which could force the Fund to liquidate investments at disadvantageous times or prices, therefore adversely affecting the Fund. 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 differently than the value realized upon such security’s sale. In times of market instability, valuation may be more difficult. Liquidity risk is the risk that fixed-income securities may be difficult or impossible to sell at the time that the portfolio managers would like or at the price the portfolio managers believe the security is currently worth. Sovereign Debt Risk. The Fund may invest in U.S. and non-U.S. 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. A sovereign debtor’s willingness or ability to satisfy its debt obligation may be affected by various factors including, but not limited to, its cash flow situation, the extent of its foreign currency reserves, the availability of foreign exchange when a payment is due, and the relative size of its debt position in relation to its economy as a whole. In the event of default, there may be limited or no legal remedies for collecting sovereign debt and there may be no bankruptcy proceedings through which the Fund may collect all or part of the sovereign debt that a governmental entity has not repaid. In addition, to the extent the Fund invests in non-U.S. sovereign debt it may be subject to currency risk. Mortgage-Backed Securities Risk. Mortgage-backed securities are classified generally as either commercial mortgage-backed securities or residential mortgage-backed securities, each of which is subject to certain specific risks. Mortgage-backed securities tend to be more sensitive to changes in interest rates than other types of debt 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. 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. Management Risk. The Fund is an actively managed investment portfolio and is therefore subject to the risk that the investment strategies employed for the Fund may fail to produce the intended results. The Fund may underperform its benchmark index or other mutual funds with similar investment objectives. 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 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 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/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 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	1-800-525-3713
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:  3rd Quarter 2009  10.97%          Worst Quarter:  3rd Quarter 2011  −11.02%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns (periods ended 12/31/14)
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 Narrative	rr_PerformanceTableNarrativeTextBlock	The Barclays U.S. Aggregate Bond Index is made up of the Barclays U.S. Government/Corporate Bond Index, Mortgage-Backed Securities Index, and Asset-Backed Securities Index, including securities that are of investment grade quality or better, have at least one year to maturity, and have an outstanding par value of at least $100 million. The Balanced Index is an internally-calculated, hypothetical combination of unmanaged indices that combines total returns from the S&P 500® Index (55%) and the Barclays U.S. Aggregate Bond Index (45%). 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 Balanced 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	0.18%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.73%
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class D Shares
1 Year	rr_ExpenseExampleYear01	75
3 Years	rr_ExpenseExampleYear03	233
5 Years	rr_ExpenseExampleYear05	406
10 Years	rr_ExpenseExampleYear10	906
2005	rr_AnnualReturn2005	7.75%
2006	rr_AnnualReturn2006	10.56%
2007	rr_AnnualReturn2007	10.15%
2008	rr_AnnualReturn2008	(15.22%)
2009	rr_AnnualReturn2009	24.28%
2010	rr_AnnualReturn2010	7.83%
2011	rr_AnnualReturn2011	1.44%
2012	rr_AnnualReturn2012	13.07%
2013	rr_AnnualReturn2013	19.72%
2014	rr_AnnualReturn2014	8.46%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	10.97%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2011
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(11.02%)
Janus Balanced 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	8.46%
5 Years	rr_AverageAnnualReturnYear05	9.94%
10 Years	rr_AverageAnnualReturnYear10	8.31%
Since Inception	rr_AverageAnnualReturnSinceInception	10.11%
Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 01, 1992
Janus Balanced 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	6.69%
5 Years	rr_AverageAnnualReturnYear05	8.67%
10 Years	rr_AverageAnnualReturnYear10	7.26%
Since Inception	rr_AverageAnnualReturnSinceInception	8.62%
Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 01, 1992
Janus Balanced 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
1 Year	rr_AverageAnnualReturnYear01	5.80%
5 Years	rr_AverageAnnualReturnYear05	7.71%
10 Years	rr_AverageAnnualReturnYear10	6.55%
Since Inception	rr_AverageAnnualReturnSinceInception	8.03%
Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 01, 1992
Janus Balanced Fund | Class D 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	13.69%
5 Years	rr_AverageAnnualReturnYear05	15.45%
10 Years	rr_AverageAnnualReturnYear10	7.67%
Since Inception	rr_AverageAnnualReturnSinceInception	9.58%
Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 01, 1992
Janus Balanced Fund | Class D Shares | Barclays U.S. Aggregate Bond Index (reflects no deduction for expenses, fees, or taxes)
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Barclays U.S. Aggregate Bond Index
1 Year	rr_AverageAnnualReturnYear01	5.97%
5 Years	rr_AverageAnnualReturnYear05	4.45%
10 Years	rr_AverageAnnualReturnYear10	4.71%
Since Inception	rr_AverageAnnualReturnSinceInception	5.89%
Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 01, 1992
Janus Balanced Fund | Class D Shares | Balanced Index (reflects no deduction for expenses, fees, or taxes)
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Balanced Index
1 Year	rr_AverageAnnualReturnYear01	10.23%
5 Years	rr_AverageAnnualReturnYear05	10.64%
10 Years	rr_AverageAnnualReturnYear10	6.57%
Since Inception	rr_AverageAnnualReturnSinceInception	8.22%
Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 01, 1992