Vanguard Mortgage-Backed Securities Index Fund Average Annual Total Returns - Institutional Prospectus [Member] |
12 Months Ended | 60 Months Ended | 120 Months Ended |
|---|---|---|---|
Dec. 31, 2024 |
Dec. 31, 2024 |
Dec. 31, 2024 |
|
| Bloomberg U.S. MBS Float Adjusted Index (reflects no deduction for fees, expenses, or taxes)[Member] | |||
| Prospectus [Line Items] | |||
| Average Annual Return, Percent | 1.54% | (0.57%) | 0.96% |
| Bloomberg U.S. Aggregate Float Adjusted Index (reflects no deduction for fees, expenses, or taxes)[Member] | |||
| Prospectus [Line Items] | |||
| Average Annual Return, Percent | 1.33% | (0.27%) | 1.39% |
| Institutional Shares | |||
| Prospectus [Line Items] | |||
| Average Annual Return, Percent | 1.42% | (0.72%) | 0.86% |
| Institutional Shares | After Taxes on Distributions | |||
| Prospectus [Line Items] | |||
| Average Annual Return, Percent | (0.18%) | (1.73%) | (0.16%) |
| Institutional Shares | After Taxes on Distributions and Sales | |||
| Prospectus [Line Items] | |||
| Average Annual Return, Percent | 0.83% | (0.96%) | 0.22% |