Index 400 Stock Portfolio Investment Strategy - Index 400 Stock Portfolio	Dec. 31, 2025
Prospectus [Line Items]
Strategy [Heading]	<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">PRINCIPAL INVESTMENT STRATEGIES</span>
Strategy Narrative [Text Block]	The Portfolio employs a “passive management,” or indexing, investment approach designed to track the performance of the S&P MidCap 400® Index. The S&P MidCap 400® Index is composed of the stocks of companies whose capitalizations generally are smaller than those of companies that comprise the S&P 500® Index. The S&P MidCap 400® Index does not include the stocks of the very large companies that account for most of the weighting in the S&P 500® Index. As of March 31, 2026, the market capitalization range of the S&P MidCap 400® Index was approximately $1.66 billion to $27.65 billion. Normally, the Portfolio invests at least 80% of net assets (plus any borrowings for investment purposes) in stocks included in the underlying index. Further, the Portfolio attempts to achieve its objective by investing all, or substantially all, of its assets in the stocks that make up the S&P MidCap 400® Index, holding each stock in approximately the same proportion as its weighting in the Index. This is known as a full replication strategy. The Portfolio may also invest in equity index futures and exchange traded funds for cash management and liquidity purposes and to help achieve full replication. Standard & Poor’s constructs the index by first identifying major industry categories and then allocating a representative sample of the larger and more liquid stocks in those industries to the index. S&P weights each stock according to its float-adjusted market value. For example, the 50 largest companies in the index may account for over 50% of its value. The approach employed by the Portfolio with respect to reconstitution and rebalancing aligns with the process followed generally by the S&P MidCap 400® Index. Changes to the underlying company constituents of the S&P MidCap 400® Index are made on an as-needed basis and are usually announced several days before they are scheduled to be implemented. The S&P MidCap 400® Index typically makes weightings adjustments based on changes in the amount of a constituent company’s shares outstanding on a quarterly basis. The constituent and share-based weightings changes made by S&P MidCap 400® Index will be made in a parallel fashion by the Portfolio on substantially the same timeline. Because the Portfolio pursues an investment strategy of full replication of the underlying S&P MidCap 400® Index, the investments in the Portfolio will be concentrated in a particular industry only to the extent that the S&P MidCap 400® Index is also concentrated in that industry. Similarly, to the extent that the underlying S&P MidCap 400® Index has a relatively high percentage of its assets invested in a particular sector, the Portfolio may also hold a relatively high percentage of its assets in that particular sector, as well. The Portfolio utilizes cash equitization instruments, and rebalancing occurs as necessary to maintain balances within established target ranges for these instruments. Cash equitization as employed by the Portfolio is a strategy pursuant to which the Portfolio will acquire certain derivative instruments, such as equity index futures, whereby the futures will be utilized to replicate index returns and enable the Portfolio to be fully invested, while still maintaining cash balances as needed by the Portfolio. This strategy works to limit the extent to which uninvested cash will weigh negatively on overall Portfolio returns when markets go up. The Index 400 Stock Portfolio’s ability to match the performance of the S&P MidCap 400® Index will be affected to some extent by the size and timing of cash flows into and out of the Index 400 Stock Portfolio. The Portfolio will be managed with a view to reducing such effects.

Index 400 Stock Portfolio Investment Strategy - Index 400 Stock Portfolio

Dec. 31, 2025

<span style="color:#000000;font-family:Arial;font-size:10.02pt;font-weight:bold;">PRINCIPAL INVESTMENT STRATEGIES</span>

Strategy Narrative [Text Block]

The Portfolio employs a “passive management,” or indexing, investment approach designed to track the performance of the S&P MidCap 400® Index. The S&P MidCap 400® Index is composed of the stocks of companies whose capitalizations generally are smaller than those of companies that comprise the S&P 500® Index. The S&P MidCap 400® Index does not include the stocks of the very large companies that account for most of the weighting in the S&P 500® Index. As of March 31, 2026, the market capitalization range of the S&P MidCap 400® Index was approximately $1.66 billion to $27.65 billion. Normally, the Portfolio invests at least 80% of net assets (plus any borrowings for investment purposes) in stocks included in the underlying index. Further, the Portfolio attempts to achieve its objective by investing all, or substantially all, of its assets in the stocks that make up the S&P MidCap 400® Index, holding each stock in approximately the same proportion as its weighting in the Index. This is known as a full replication strategy. The Portfolio may also invest in equity index futures and exchange traded funds for cash management and liquidity purposes and to help achieve full replication. Standard & Poor’s constructs the index by first identifying major industry categories and then allocating a representative sample of the larger and more liquid stocks in those industries to the index. S&P weights each stock according to its float-adjusted market value. For example, the 50 largest companies in the index may account for over 50% of its value. The approach employed by the Portfolio with respect to reconstitution and rebalancing aligns with the process followed generally by the S&P MidCap 400® Index. Changes to the underlying company constituents of the S&P MidCap 400® Index are made on an as-needed basis and are usually announced several days before they are scheduled to be implemented. The S&P MidCap 400® Index typically makes weightings adjustments based on changes in the amount of a constituent company’s shares outstanding on a quarterly basis. The constituent and share-based weightings changes made by S&P MidCap 400® Index will be made in a parallel fashion by the Portfolio on substantially the same timeline. Because the Portfolio pursues an investment strategy of full replication of the underlying S&P MidCap 400® Index, the investments in the Portfolio will be concentrated in a particular industry only to the extent that the S&P MidCap 400® Index is also concentrated in that industry. Similarly, to the extent that the underlying S&P MidCap 400® Index has a relatively high percentage of its assets invested in a particular sector, the Portfolio may also hold a relatively high percentage of its assets in that particular sector, as well. The Portfolio utilizes cash equitization instruments, and rebalancing occurs as necessary to maintain balances within established target ranges for these instruments. Cash equitization as employed by the Portfolio is a strategy pursuant to which the Portfolio will acquire certain derivative instruments, such as equity index futures, whereby the futures will be utilized to replicate index returns and enable the Portfolio to be fully invested, while still maintaining cash balances as needed by the Portfolio. This strategy works to limit the extent to which uninvested cash will weigh negatively on overall Portfolio returns when markets go up. The Index 400 Stock Portfolio’s ability to match the performance of the S&P MidCap 400® Index will be affected to some extent by the size and timing of cash flows into and out of the Index 400 Stock Portfolio. The Portfolio will be managed with a view to reducing such effects.