Vanguard SP Mid-Cap 400 Index Fund Average Annual Total Returns - Institutional Prospectus [Member] |
12 Months Ended | 60 Months Ended | 69 Months Ended | 118 Months Ended | 120 Months Ended |
|---|---|---|---|---|---|
Dec. 31, 2024 |
Dec. 31, 2024 |
Dec. 31, 2024 |
Dec. 31, 2024 |
Dec. 31, 2024 |
|
| S&P MidCap 400 Index (reflects no deduction for fees, expenses, or taxes)[Member] | |||||
| Prospectus [Line Items] | |||||
| Average Annual Return, Percent | 13.93% | 10.34% | 9.68% | ||
| Dow Jones U.S. Total Stock Market Float Adjusted Index (reflects no deduction for fees, expenses, or taxes)[Member] | |||||
| Prospectus [Line Items] | |||||
| Average Annual Return, Percent | 23.88% | 13.78% | 14.20% | 12.36% | 12.48% |
| Institutional Shares | |||||
| Prospectus [Line Items] | |||||
| Average Annual Return, Percent | 13.85% | 10.26% | 9.61% | ||
| Institutional Shares | After Taxes on Distributions | |||||
| Prospectus [Line Items] | |||||
| Average Annual Return, Percent | 13.46% | 9.87% | 9.19% | ||
| Institutional Shares | After Taxes on Distributions and Sales | |||||
| Prospectus [Line Items] | |||||
| Average Annual Return, Percent | 8.42% | 8.06% | 7.77% |