Loomis Sayles Global Allocation Portfolio Investment Strategy - Loomis Sayles Global Allocation Portfolio	Dec. 31, 2025
Prospectus [Line Items]
Strategy [Heading]	<span style="color:#000000;font-family:Times New Roman;font-size:11.5pt;font-weight:bold;">Principal Investment Strategies</span>
Strategy Narrative [Text Block]	Loomis, Sayles & Company, L.P. (“Loomis Sayles” or “Subadviser”), subadviser to the Portfolio, invests the Portfolio’s assets, under normal circumstances, primarily in equity and fixed income securities of U.S. and foreign issuers, including securities of issuers located in countries with emerging securities markets. The Portfolio’s investments in equities will range between 50% and 70% of the Portfolio’s assets, and its investments in fixed income securities will range between 25% and 50% of the Portfolio’s assets. Loomis Sayles allocates the Portfolio’s assets among the following three sectors: (1) global equities, (2) domestic fixed income securities and (3) international fixed income securities. In deciding how to allocate the Portfolio’s assets among the three sectors, Loomis Sayles attempts to determine the relative attractiveness of each of the three sectors based on fundamental factors such as economic cycles, relative interest rates, stock market valuations, and currency considerations. In deciding which global equity securities to buy and sell, Loomis Sayles generally looks for quality companies that can grow intrinsic value and are priced at an attractive valuation. In deciding which domestic and international fixed income securities to buy and sell, Loomis Sayles generally looks for securities that it believes are undervalued and have the potential for credit upgrades. The Portfolio may invest in investment grade securities, although it may also invest up to 35% of its assets in below investment-grade securities (commonly called “junk bonds”). The Portfolio will limit its investments in securities issued in emerging market countries to no more than 50% of its assets. The Portfolio may also invest in foreign currencies and may engage in other foreign currency transactions for investment or hedging purposes. Loomis Sayles may hedge currency risk for the Portfolio (including “cross hedging” between two or more foreign currencies) if it believes the outlook for a particular foreign currency is unfavorable. Loomis Sayles may elect not to hedge currency risk, which may cause the Portfolio to incur losses that would not have been incurred had the risk been hedged. The Portfolio may engage in foreign currency hedging transactions, options for hedging and investment purposes, forward, futures and swap transactions and other derivative transactions. The Portfolio also may invest in collateralized mortgage obligations, U.S. and foreign government securities, depositary receipts, real estate investment trusts, securities issued pursuant to Rule 144A under the Securities Act of 1933 and convertible securities.

Loomis Sayles Global Allocation Portfolio Investment Strategy - Loomis Sayles Global Allocation Portfolio

Dec. 31, 2025

<span style="color:#000000;font-family:Times New Roman;font-size:11.5pt;font-weight:bold;">Principal Investment Strategies</span>

Strategy Narrative [Text Block]

Loomis, Sayles & Company, L.P. (“Loomis Sayles” or “Subadviser”), subadviser to the Portfolio, invests the Portfolio’s assets, under normal circumstances, primarily in equity and fixed income securities of U.S. and foreign issuers, including securities of issuers located in countries with emerging securities markets. The Portfolio’s investments in equities will range between 50% and 70% of the Portfolio’s assets, and its investments in fixed income securities will range between 25% and 50% of the Portfolio’s assets. Loomis Sayles allocates the Portfolio’s assets among the following three sectors: (1) global equities, (2) domestic fixed income securities and (3) international fixed income securities. In deciding how to allocate the Portfolio’s assets among the three sectors, Loomis Sayles attempts to determine the relative attractiveness of each of the three sectors based on fundamental factors such as economic cycles, relative interest rates, stock market valuations, and currency considerations. In deciding which global equity securities to buy and sell, Loomis Sayles generally looks for quality companies that can grow intrinsic value and are priced at an attractive valuation. In deciding which domestic and international fixed income securities to buy and sell, Loomis Sayles generally looks for securities that it believes are undervalued and have the potential for credit upgrades. The Portfolio may invest in investment grade securities, although it may also invest up to 35% of its assets in below investment-grade securities (commonly called “junk bonds”). The Portfolio will limit its investments in securities issued in emerging market countries to no more than 50% of its assets. The Portfolio may also invest in foreign currencies and may engage in other foreign currency transactions for investment or hedging purposes. Loomis Sayles may hedge currency risk for the Portfolio (including “cross hedging” between two or more foreign currencies) if it believes the outlook for a particular foreign currency is unfavorable. Loomis Sayles may elect not to hedge currency risk, which may cause the Portfolio to incur losses that would not have been incurred had the risk been hedged. The Portfolio may engage in foreign currency hedging transactions, options for hedging and investment purposes, forward, futures and swap transactions and other derivative transactions. The Portfolio also may invest in collateralized mortgage obligations, U.S. and foreign government securities, depositary receipts, real estate investment trusts, securities issued pursuant to Rule 144A under the Securities Act of 1933 and convertible securities.