Vanguard Mortgage-Backed Securities Index Fund Expense Example - Admiral Prospectus [Member] - Vanguard Mortgage-Backed Securities Index Fund - Admiral Shares	Aug. 31, 2025 USD ($)
Prospectus [Line Items]
Expense Example, with Redemption, 1 Year	$ 4
Expense Example, with Redemption, 3 Years	13
Expense Example, with Redemption, 5 Years	23
Expense Example, with Redemption, 10 Years	$ 51

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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