S000015790 [Member] Average Annual Total Returns |
12 Months Ended | 60 Months Ended | 120 Months Ended |
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2025 |
Dec. 31, 2025 |
|
| Bloomberg U.S. Aggregate Bond Index (reflects no deduction for fees, expenses, or taxes) | |||
| Prospectus [Line Items] | |||
| Average Annual Return, Percent | 7.30% | (0.36%) | 2.01% |
| BOND INDEX FUND | |||
| Prospectus [Line Items] | |||
| Average Annual Return, Percent | 7.23% | (0.43%) | 1.89% |
| BOND INDEX FUND | After Taxes on Distributions | |||
| Prospectus [Line Items] | |||
| Average Annual Return, Percent | 5.52% | (1.70%) | 0.65% |
| BOND INDEX FUND | After Taxes on Distributions and Sales | |||
| Prospectus [Line Items] | |||
| Average Annual Return, Percent | 4.25% | (0.86%) | 0.92% |