S000006017 [Member] Investment Objectives and Goals - Short-Term Treasury Portfolio |
Jan. 31, 2026 |
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| Prospectus [Line Items] | |
| Risk/Return [Heading] | Short-Term Treasury Portfolio June 1, 2026 PORTFOLIO SUMMARY Class I — PRTBX |
| Objective [Heading] | Investment Objective |
| Objective, Primary [Text Block] | Short-Term Treasury Portfolio seeks to earn high current income, consistent with safety and liquidity of principal.
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