S000006017 [Member] Fees and Expenses - Short-Term Treasury Portfolio	Jan. 31, 2026
Prospectus [Line Items]
Expense Heading [Optional Text]	Fees and Expenses of the Portfolio
Expense Narrative [Text Block]	The table below describes the fees and expenses you would pay if you buy, hold and sell shares of the Portfolio. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below.
Shareholder Fees Caption [Optional Text]	Shareholder Fees(fees paid directly from your investment)
Operating Expenses Caption [Optional Text]	Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment)
Expense Example [Heading]	Expense Example
Expense Example Narrative [Text Block]	This example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year, that the Portfolio’s operating expenses remain the same and that the fee waiver remains in place for the period indicated. Although your actual costs may be higher or lower, based on these assumptions, your costs would be:
Portfolio Turnover [Heading]	Portfolio Turnover
Portfolio Turnover [Text Block]	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 and may result in higher taxes when Portfolio shares are held in a taxable account. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the example above, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 16.60% of the average value of its portfolio.
Portfolio Turnover, Rate	16.60%

S000006017 [Member] Fees and Expenses - Short-Term Treasury Portfolio

Jan. 31, 2026

Fees and Expenses of the Portfolio

The table below describes the fees and expenses you would pay if you buy, hold and sell shares of the Portfolio. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below.

Shareholder Fees Caption [Optional Text]

Shareholder Fees(fees paid directly from your investment)

Operating Expenses Caption [Optional Text]

Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment)

Expense Example [Heading]

Expense Example

Expense Example Narrative [Text Block]

This example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year, that the Portfolio’s operating expenses remain the same and that the fee waiver remains in place for the period indicated. Although your actual costs may be higher or lower, based on these assumptions, your costs would be:

Portfolio Turnover [Heading]

Portfolio Turnover

Portfolio Turnover [Text Block]

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 and may result in higher taxes when Portfolio shares are held in a taxable account. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the example above, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 16.60% of the average value of its portfolio.

Portfolio Turnover, Rate

16.60%