Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	JANUS ASPEN SERIES
Prospectus Date	rr_ProspectusDate	May 01, 2014
Forty Portfolio | Service Shares
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	PORTFOLIO SUMMARY Forty Portfolio
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Forty Portfolio seeks long-term growth of capital.
Expense [Heading]	rr_ExpenseHeading	FEES AND EXPENSES OF THE PORTFOLIO
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 Portfolio. Owners of variable insurance contracts that invest in the Shares should refer to the variable insurance contract prospectus for a description of fees and expenses, as the following table and examples do not reflect deductions at the separate account level or contract level for any charges that may be incurred under a contract. Inclusion of these charges would increase the fees and expenses described below.
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 Portfolio 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. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s turnover rate was 61% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	61.00%
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE:
Expense Example by Year [Heading]	rr_ExpenseExampleByYearHeading	The Example assumes that you invest $10,000 in the Portfolio 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 Portfolio’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 Portfolio with the cost of investing in other mutual funds.
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Portfolio pursues its investment objective by normally investing primarily in a core group of 20-40 common stocks selected for their growth potential. The Portfolio may invest in companies of any size, from larger, well-established companies to smaller, emerging growth companies. The Portfolio may also invest in foreign securities, which may include investments in emerging markets. The portfolio manager applies a “bottom up” approach in choosing investments. In other words, the portfolio manager looks at companies one at a time to determine if a company is an attractive investment opportunity and if it is consistent with the Portfolio’s investment policies. The Portfolio 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 Portfolio’s returns will vary, and you could lose money. The Portfolio 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. Market Risk. The value of the Portfolio’s holdings may decrease if the value of an individual company or security, or multiple companies or securities, in the Portfolio decreases or if the portfolio manager’s belief about a company’s intrinsic worth is incorrect. Further, regardless of how well individual companies or securities perform, the value of the Portfolio’s holdings could also decrease if there are deteriorating economic or market conditions. It is important to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money. Growth Securities Risk. The Portfolio 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 manager’s perception of a company’s growth potential is not realized, the securities purchased may not perform as expected, reducing the Portfolio’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. Nondiversification Risk. The Portfolio is classified as nondiversified under the Investment Company Act of 1940, as amended. This gives the portfolio manager more flexibility to hold larger positions in a smaller number of securities. As a result, an increase or decrease in the value of a single security held by the Portfolio may have a greater impact on the Portfolio’s NAV and total return. Foreign Exposure Risk. The Portfolio 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 Portfolio 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 Portfolio has invested a significant amount of its assets may have a greater effect on the Portfolio’s performance than it would in a more geographically diversified portfolio. To the extent the Portfolio 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. Securities Lending Risk. The Portfolio 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 Portfolio may experience delays and costs in recovering the security or gaining access to the collateral provided to the Portfolio to collateralize the loan. If the Portfolio is unable to recover a security on loan, the Portfolio 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 Portfolio. Management Risk. The Portfolio is an actively managed investment portfolio and is therefore subject to the risk that the investment strategies employed for the Portfolio may fail to produce the intended results. The Portfolio may underperform its benchmark index or other mutual funds with similar investment objectives. An investment in the Portfolio 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 Portfolio’s returns will vary, and you could lose money.
Risk Nondiversified Status [Text]	rr_RiskNondiversifiedStatus	Nondiversification Risk. The Portfolio is classified as nondiversified under the Investment Company Act of 1940, as amended. This gives the portfolio manager more flexibility to hold larger positions in a smaller number of securities. As a result, an increase or decrease in the value of a single security held by the Portfolio may have a greater impact on the Portfolio’s NAV and total return.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Portfolio 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 Portfolio by showing how the Portfolio’s performance has varied over time. The Portfolio’s Service Shares commenced operations on December 31, 1999. The returns shown for the Service Shares for periods prior to December 31, 1999 reflect the historical performance of a different class of shares (the Institutional Shares), restated based on the Service Shares’ estimated fees and expenses (ignoring any fee and expense limitations). The bar chart depicts the change in performance from year to year during the periods indicated, but does not include charges or expenses attributable to any insurance product, which would lower the performance illustrated. The Portfolio does not impose any sales or other charges that would affect total return computations. Total return figures include the effect of the Portfolio’s expenses. The table compares the average annual returns for the Service Shares of the Portfolio 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. The Portfolio’s past performance does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/variable-insurance 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 Portfolio by showing how the Portfolio’s performance has varied over time. The bar chart depicts the change in performance from year to year during the periods indicated, but does not include charges or expenses attributable to any insurance product, which would lower the performance illustrated.
Performance Additional Market Index [Text]	rr_PerformanceAdditionalMarketIndex	The table compares the average annual returns for the Service Shares of the Portfolio 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/variable-insurance
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Portfolio’s past performance does not necessarily indicate how it will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Annual Total Returns for Service Shares (calendar year-end)
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best Quarter:  2nd Quarter 2009  22.06%          Worst Quarter:  3rd Quarter 2008  −25.39%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns (periods ended 12/31/13)
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	The Russell 1000® Growth Index measures the performance of those Russell 1000® companies with higher price-to-book ratios and higher forecasted growth values. This index is used to calculate the performance fee adjustment.
Performance Table Closing [Text Block]	rr_PerformanceTableClosingTextBlock	Updated performance information is available at janus.com/variable-insurance or by calling 1-877-335-2687.
Forty Portfolio | Service Shares | Service Shares, Forty Portfolio
Risk/Return:	rr_RiskReturnAbstract
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	Service Shares
Management Fees (may adjust up or down)	rr_ManagementFeesOverAssets	0.49%
Distribution/Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.07%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.81%
Expense Example, By Year, Column [Text]	rr_ExpenseExampleByYearColumnName	Service Shares
1 Year	rr_ExpenseExampleYear01	$ 83
3 Years	rr_ExpenseExampleYear03	259
5 Years	rr_ExpenseExampleYear05	450
10 Years	rr_ExpenseExampleYear10	$ 1,002
2004	rr_AnnualReturn2004	17.97%
2005	rr_AnnualReturn2005	12.56%
2006	rr_AnnualReturn2006	9.12%
2007	rr_AnnualReturn2007	36.63%
2008	rr_AnnualReturn2008	(44.31%)
2009	rr_AnnualReturn2009	46.01%
2010	rr_AnnualReturn2010	6.48%
2011	rr_AnnualReturn2011	(6.94%)
2012	rr_AnnualReturn2012	23.86%
2013	rr_AnnualReturn2013	30.89%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	22.06%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(25.39%)
Column	rr_AverageAnnualReturnColumnName	Service Shares
1 Year	rr_AverageAnnualReturnYear01	30.89%
5 Years	rr_AverageAnnualReturnYear05	18.59%
10 Years	rr_AverageAnnualReturnYear10	9.97%
Since Inception	rr_AverageAnnualReturnSinceInception	10.77%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 01, 1997
Forty Portfolio | Service Shares | Russell 1000® Growth Index (reflects no deduction for fees, expenses, or taxes)
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Russell 1000® Growth Index
1 Year	rr_AverageAnnualReturnYear01	33.48%
5 Years	rr_AverageAnnualReturnYear05	20.39%
10 Years	rr_AverageAnnualReturnYear10	7.83%
Since Inception	rr_AverageAnnualReturnSinceInception	6.29%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 01, 1997
Forty Portfolio | Service Shares | S&P 500® Index (reflects no deduction for fees, expenses, or taxes)
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	S&P 500® Index
1 Year	rr_AverageAnnualReturnYear01	32.39%
5 Years	rr_AverageAnnualReturnYear05	17.94%
10 Years	rr_AverageAnnualReturnYear10	7.41%
Since Inception	rr_AverageAnnualReturnSinceInception	7.10%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 01, 1997