S000006017 [Member] Annual Total Returns |
12 Months Ended | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
Dec. 31, 2022 |
Dec. 31, 2021 |
Dec. 31, 2020 |
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Short-Term Treasury Portfolio | Class I | ||||||||||
| Prospectus [Line Items] | ||||||||||
| Annual Return [Percent] | 4.19% | 4.11% | 3.79% | (2.28%) | (0.74%) | 0.10% | 1.76% | 1.16% | 0.12% | (0.25%) |