Vanguard Long-Term Treasury Index Fund Expense Example - Institutional Prospectus [Member] - Vanguard Long-Term Treasury Index Fund - Institutional Shares	Aug. 31, 2025 USD ($)
Prospectus [Line Items]
Expense Example, with Redemption, 1 Year	$ 3
Expense Example, with Redemption, 3 Years	10
Expense Example, with Redemption, 5 Years	17
Expense Example, with Redemption, 10 Years	$ 39

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