Janus Henderson Mid Cap Value Portfolio Investment Risks - Institutional Shares [Member] - Janus Henderson Mid Cap Value Portfolio	Dec. 31, 2025
Market Risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Market Risk. The value of the Portfolio’s holdings may decrease due to short-term market movements and over more prolonged market downturns. As a result, the Portfolio’s net asset value may fluctuate and it may be more difficult to value or sell the Portfolio’s holdings. Market risk may affect a single issuer, industry, economic sector, or the market as a whole. Market risk may be magnified if certain social, political, economic, and other conditions and events (such as financial institution failures, economic recessions, tariffs, trade disputes, terrorism, war, armed conflicts, including related sanctions, social unrest, natural disasters, and epidemics and pandemics) adversely interrupt the global economy and financial markets. 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.
Value Investing Risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Value Investing Risk. Because different types of stocks tend to shift in and out of favor depending on market and economic conditions, “value” stocks may perform differently than other types of stocks and from the market as a whole, and can continue to be undervalued by the market for long periods of time. It is also possible that a value stock will never appreciate to the extent expected.
Mid-Sized Companies Risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Mid-Sized Companies Risk. Investments in securities issued by mid-sized companies may involve greater risks than are customarily associated with larger, more established companies. Securities issued by mid-sized companies tend to be more volatile than securities issued by larger or more established companies and may underperform as compared to the securities of larger or more established companies. These holdings are also subject to wider price fluctuations and tend to be less liquid than stocks of larger or more established companies, which could have a significant adverse effect on the Portfolio’s returns, especially as market conditions change.
Portfolio Management Risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Portfolio Management Risk. The Portfolio is an actively managed investment portfolio and is therefore subject to the risk that the investment strategies and research process employed for the Portfolio may fail to produce the intended results. Accordingly, the Portfolio may underperform benchmark indices or other funds with similar investment objectives.
Equity Securities Risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Equity Securities Risk. Equity securities are subject to changes in value, and their values may be more volatile than those of other asset classes. 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. 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 or perceptions regarding the industries in which the issuers of securities the Portfolio holds participate.
REIT Risk [Member]
Prospectus [Line Items]
Risk [Text Block]	REIT Risk.  REITs are subject to certain risks inherent in the direct ownership of real estate, including without limitation, a possible lack of mortgage funds and associated interest rate risks, overbuilding, property vacancies, increases in property taxes and operating expenses, changes in zoning laws, losses due to environmental damages and changes in neighborhood values and appeal to purchasers. In addition, a REIT could fail to qualify for tax-free pass-through of its income under the Internal Revenue Code of 1986, as amended, 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 Portfolio. Dividends received by the Portfolio from a REIT generally will not constitute qualified dividend income.
Initial Public Offering Risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Initial Public Offering Risk. The Portfolio’s purchase of shares issued in an initial public offering (“IPO”) exposes it to the risks associated with companies that have little operating history as public companies, as well as to the risks inherent in those sectors of the market where these new issuers operate. There can be no assurance that the Portfolio will identify favorable IPO investment opportunities.
Foreign Exposure Risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Foreign Exposure Risk. Foreign markets can be more volatile than the U.S. market. As a result, the Portfolio’s returns and net asset value may be affected by fluctuations in currency exchange rates or political or economic conditions in a particular country. Investments in foreign securities, particularly those of issuers located in emerging market countries, tend to have greater exposure to liquidity risk than domestic securities. 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.
ESG Integration Risk [Member]
Prospectus [Line Items]
Risk [Text Block]	ESG Integration Risk. There is a risk that considering ESG Factors as part of the Portfolio’s investment process may fail to produce the intended results or that the Portfolio may perform differently from funds that have a similar investment style but do not formally incorporate such considerations in their strategy. Information related to ESG Factors provided by issuers and third parties, which portfolio management may utilize, continues to develop and may be incomplete or inaccurate, use different or inconsistent methodologies, or be applied differently across issuers and industries.
Risk Lose Money [Member]
Prospectus [Line Items]
Risk [Text Block]	The biggest risk is that the Portfolio’s returns will vary, and you could lose money.
Risk Not Insured Depository Institution [Member]
Prospectus [Line Items]
Risk [Text Block]	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.