S000015790 [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 |
|
| BOND INDEX FUND | BOND INDEX FUND | ||||||||||
| Prospectus [Line Items] | ||||||||||
| Annual Return [Percent] | 7.23% | 1.13% | 5.46% | (12.98%) | (1.66%) | 7.33% | 8.62% | (0.16%) | 3.47% | 2.33% |