Vanguard Long-Term Bond Index Fund Average Annual Total Returns - Admiral Prospectus [Member] |
12 Months Ended | 60 Months Ended | 83 Months Ended | 120 Months Ended | |
|---|---|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2025 |
Dec. 31, 2025 |
Dec. 31, 2025 |
Dec. 31, 2025 |
|
| Bloomberg U.S. Long Gov/Credit Float Adjusted Index (reflects no deduction for fees, expenses, or taxes)[Member] | |||||
| Prospectus [Line Items] | |||||
| Average Annual Return, Percent | 6.62% | (4.89%) | 0.76% | ||
| Bloomberg U.S. Aggregate Float Adjusted Index (reflects no deduction for fees, expenses, or taxes)[Member] | |||||
| Prospectus [Line Items] | |||||
| Average Annual Return, Percent | 7.21% | (0.37%) | 1.90% | 2.05% | |
| Admiral Shares | |||||
| Prospectus [Line Items] | |||||
| Average Annual Return, Percent | 6.02% | (4.99%) | 0.67% | ||
| Performance Inception Date | Feb. 07, 2019 | ||||
| Admiral Shares | After Taxes on Distributions | |||||
| Prospectus [Line Items] | |||||
| Average Annual Return, Percent | 4.04% | (6.53%) | (0.99%) | ||
| Admiral Shares | After Taxes on Distributions and Sales | |||||
| Prospectus [Line Items] | |||||
| Average Annual Return, Percent | 3.54% | (4.29%) | (0.08%) |