Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	JANUS INVESTMENT FUND
Prospectus Date	rr_ProspectusDate	Dec. 22, 2014
INTECH U.S. Managed Volatility Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	FUND SUMMARY INTECH U.S. Managed Volatility Fund (formerly named INTECH U.S. Value Fund)
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	INTECH U.S. Managed Volatility Fund seeks long-term 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.
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 150% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	150.00%
Acquired Fund Fees and Expenses, Based on Estimates [Text]	rr_AcquiredFundFeesAndExpensesBasedOnEstimates	“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. Acquired fund fees and expenses are indirect expenses a fund may incur as a result of investing in shares of an underlying fund. Such amounts are estimated based on the annualized expenses that the Shares expect to incur.
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 invests, under normal circumstances, at least 80% of its net assets in U.S. common stocks from the universe of the Russell 1000® Index, utilizing INTECH’s mathematical investment process, applying a managed volatility approach. The Russell 1000® Index is an unmanaged index that measures the performance of the large-cap segment of the U.S. equity universe. The Fund seeks to produce returns in excess of the Russell 1000® Index, but with lower absolute volatility than the benchmark index. The Fund seeks to generate such excess returns with absolute volatility that can range from approximately 0% to 40% lower than the Russell 1000® Index. In this context, absolute volatility refers to the variation in the returns of the Fund and the benchmark index as measured by standard deviation. This range is expected to be closer to 0% in less volatile markets and will increase as market conditions become more volatile. The Fund pursues its investment objective by applying a mathematical investment process to construct an investment portfolio from the universe of stocks within the named benchmark index. The goal of this process is to combine stocks that individually have higher relative volatility, lower absolute volatility, and lower correlations with each other in an effort to reduce the Fund’s absolute volatility, while still generating returns that exceed the named benchmark index over a full market cycle (a time period representing a significant market decline and recovery). Although the Fund may underperform its named benchmark index in sharply rising markets, this strategy seeks to participate in normal rising markets and lessen losses in down markets. In applying this strategy, INTECH establishes target proportions of its holdings from stocks within the named benchmark index using an optimization process designed to determine the most effective weightings of each stock in the Fund. Once INTECH determines such proportions and the Fund’s investments are selected, the Fund is periodically rebalanced to the set target proportions and re-optimized. The rebalancing techniques used by INTECH may result in a higher portfolio turnover rate compared to a “buy and hold” fund strategy. The Fund may lend portfolio securities on a short-term or long-term basis, in an amount equal to up to one-third of its total assets as determined at the time of the loan origination.
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 equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices. Investment Process Risk. The focus on managed volatility may keep the Fund from achieving excess returns over the named benchmark index. In this regard, INTECH’s managed volatility strategy may underperform the Fund’s named benchmark index during certain periods of up markets, and in particular, most likely will underperform the benchmark index in sharply rising markets, and may not achieve the desired level of protection in down markets. As INTECH’s mathematical investment process has evolved, it has experienced periods of both underperformance and outperformance relative to an identified benchmark index. Even when the proprietary mathematical investment process is working appropriately, INTECH expects that there will be periods of underperformance relative to the benchmark index. On an occasional basis, INTECH makes changes to its mathematical investment process that do not require shareholder notice. These changes may result in changes to the portfolio, might not provide the intended results, and may adversely impact the Fund’s performance. 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. 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. Real Estate Securities Risk. The Fund’s performance may be affected by the risks associated with investments in real estate-related companies. The value of real estate-related companies’ securities 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 company. Investments in real estate investment trusts (“REITs”) involve the same risks as other real estate investments. In addition, a REIT could fail to qualify for tax-free pass-through of its income under the Internal Revenue Code or fail to maintain its exemption from registration under the Investment Company Act of 1940, as amended, which could produce adverse economic consequences for the REIT and its investors, including the Fund. 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. Securities Lending Risk. The Fund may seek to earn additional income through lending its securities to certain qualified broker-dealers and institutions. There is the risk that when portfolio securities are lent, the securities may not be returned on a timely basis, and the Fund may experience delays and costs in recovering the security or gaining access to the collateral provided to the Fund to collateralize the loan. If the Fund is unable to recover a security on loan, the Fund may use the collateral to purchase replacement securities in the market. There is a risk that the value of the collateral could decrease below the cost of the replacement security by the time the replacement investment is made, resulting in a loss to the Fund. 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 December 22, 2014. The performance shown for Class D Shares for the period July 6, 2009 to December 31, 2013, reflects the performance of the Fund’s Class I Shares, calculated using the fees and expenses of Class D Shares, without the effect of any fee and expense limitations or waivers. Performance shown for periods prior to July 6, 2009, reflects the historical performance of the Janus Adviser INTECH Risk-Managed Value Fund’s (“JAD predecessor fund”) Class I Shares prior to the reorganization of Class I Shares of the JAD predecessor fund into Class I Shares of the Fund, calculated using the fees and expenses of Class D Shares, without the effect of any fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to December 31, 2013, the performance shown may have been different. 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:  Third Quarter 2009  17.77%          Worst Quarter:  Fourth Quarter 2008  −21.39%
Year to Date Return, Label	rr_YearToDateReturnLabel	The Fund’s year-to-date return as of the calendar quarter ended September 30, 2014 was 4.47%.
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns (periods ended 12/31/13)
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	Effective December 17, 2014, the Fund’s primary benchmark index changed from the Russell 1000® Value Index to the Russell 1000® Index. The transition to the Russell 1000® Index is expected to provide shareholders with broader exposure to large cap U.S. equities than the former value-focused index, including exposure to growth and value stock constituents, and the potential benefits from the resulting application of INTECH’s managed volatility investment process across the entire Russell 1000® Index investment universe. The Russell 1000® Index measures the performance of the large-cap segment of the U.S. equity universe. After-tax returns are calculated using distributions for the Fund’s Class I Shares for periods following July 6, 2009; and for the JAD predecessor fund’s Class I Shares for periods prior to July 6, 2009. 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.
INTECH U.S. Managed Volatility Fund | Class D
Risk/Return:	rr_RiskReturnAbstract
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Class D
Management Fees	rr_ManagementFeesOverAssets	0.50%
Other Expenses	rr_OtherExpensesOverAssets	0.32%	[1]
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.83%
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Class D Shares
1 Year	rr_ExpenseExampleYear01	85
3 Years	rr_ExpenseExampleYear03	265
5 Years	rr_ExpenseExampleYear05	460
10 Years	rr_ExpenseExampleYear10	1,025
2006	rr_AnnualReturn2006	17.45%
2007	rr_AnnualReturn2007	1.25%
2008	rr_AnnualReturn2008	(34.93%)
2009	rr_AnnualReturn2009	17.72%
2010	rr_AnnualReturn2010	15.33%
2011	rr_AnnualReturn2011	2.12%
2012	rr_AnnualReturn2012	15.44%
2013	rr_AnnualReturn2013	35.70%
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2014
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	4.47%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	17.77%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(21.39%)
INTECH U.S. Managed Volatility Fund | 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	35.70%
5 Years	rr_AverageAnnualReturnYear05	16.78%
Since Inception of Predecessor Fund	rr_AverageAnnualReturnSinceInception	6.70%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 30, 2005
INTECH U.S. Managed Volatility Fund | 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	29.77%
5 Years	rr_AverageAnnualReturnYear05	15.49%
Since Inception of Predecessor Fund	rr_AverageAnnualReturnSinceInception	5.65%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 30, 2005
INTECH U.S. Managed Volatility Fund | 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	23.29%
5 Years	rr_AverageAnnualReturnYear05	13.43%
Since Inception of Predecessor Fund	rr_AverageAnnualReturnSinceInception	5.11%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 30, 2005
INTECH U.S. Managed Volatility Fund | Russell 1000® Index (reflects no deduction for expenses, fees, or taxes)
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Russell 1000® Index
1 Year	rr_AverageAnnualReturnYear01	33.11%
5 Years	rr_AverageAnnualReturnYear05	18.59%
Since Inception of Predecessor Fund	rr_AverageAnnualReturnSinceInception	7.53%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 30, 2005
INTECH U.S. Managed Volatility Fund | Russell 1000® Value Index (reflects no deduction for expenses, fees, or taxes)
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Russell 1000® Value Index
1 Year	rr_AverageAnnualReturnYear01	32.53%
5 Years	rr_AverageAnnualReturnYear05	16.67%
Since Inception of Predecessor Fund	rr_AverageAnnualReturnSinceInception	6.58%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 30, 2005

[1] Other Expenses are based on the estimated annualized expenses that the Shares expect to incur.

[2] “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. Acquired fund fees and expenses are indirect expenses a fund may incur as a result of investing in shares of an underlying fund. Such amounts are estimated based on the annualized expenses that the Shares expect to incur.