MFS Research International Portfolio Investment Strategy - MFS Research International 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]	Massachusetts Financial Services Company (“MFS” or “Subadviser”), subadviser to the Portfolio, invests the Portfolio’s assets, under normal circumstances, primarily in foreign equity securities, including emerging market equity securities. Equity securities include common stocks, preferred stocks, and depositary receipts for those securities. The Portfolio may invest a large percentage of its assets in issuers in a single country, a small number of countries, or a particular geographic region. In selecting investments for the Portfolio, MFS is not constrained by any particular investment style. MFS may invest the Portfolio’s assets in the stocks of companies it believes to have above average earnings growth potential compared to other companies (growth companies), in the stocks of companies it believes are undervalued compared to their perceived worth (value companies), or in a combination of growth and value companies. The Portfolio may invest in companies of any size. In conjunction with a team of investment research analysts, sector leaders select investments for the Portfolio. MFS generally manages the Portfolio to be sector neutral to the MSCI Europe, Australia and Far East (EAFE)® Index (the “Index”) using MFS’s custom industry and sector categories to classify the Portfolio’s and the Index’s holdings. MFS uses an active bottom-up investment approach to buying and selling investments for the Portfolio. Investments are selected primarily based on fundamental analysis of individual issuers and their potential in light of their financial condition, and market, economic, political, and regulatory conditions. Factors considered may include analysis of an issuer’s earnings, cash flows, competitive position, and management ability. Quantitative screening tools that systematically evaluate an issuer’s valuation, price and earnings momentum, earnings quality, and other factors, may also be considered.

MFS Research International Portfolio Investment Strategy - MFS Research International 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]

Massachusetts Financial Services Company (“MFS” or “Subadviser”), subadviser to the Portfolio, invests the Portfolio’s assets, under normal circumstances, primarily in foreign equity securities, including emerging market equity securities. Equity securities include common stocks, preferred stocks, and depositary receipts for those securities. The Portfolio may invest a large percentage of its assets in issuers in a single country, a small number of countries, or a particular geographic region. In selecting investments for the Portfolio, MFS is not constrained by any particular investment style. MFS may invest the Portfolio’s assets in the stocks of companies it believes to have above average earnings growth potential compared to other companies (growth companies), in the stocks of companies it believes are undervalued compared to their perceived worth (value companies), or in a combination of growth and value companies. The Portfolio may invest in companies of any size. In conjunction with a team of investment research analysts, sector leaders select investments for the Portfolio. MFS generally manages the Portfolio to be sector neutral to the MSCI Europe, Australia and Far East (EAFE)® Index (the “Index”) using MFS’s custom industry and sector categories to classify the Portfolio’s and the Index’s holdings. MFS uses an active bottom-up investment approach to buying and selling investments for the Portfolio. Investments are selected primarily based on fundamental analysis of individual issuers and their potential in light of their financial condition, and market, economic, political, and regulatory conditions. Factors considered may include analysis of an issuer’s earnings, cash flows, competitive position, and management ability. Quantitative screening tools that systematically evaluate an issuer’s valuation, price and earnings momentum, earnings quality, and other factors, may also be considered.