Annual Fund Operating Expenses (Vanguard Extended Duration Treasury Index Fund)	12 Months Ended
Aug. 31, 2011
Vanguard Extended Duration Treasury Index Fund - ETF Shares
Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)
Management Expenses	0.08%
12b-1 Distribution Fee	none
Other Expenses	0.05%
Total Annual Fund Operating Expenses	0.13%
Vanguard Extended Duration Treasury Index Fund - Institutional Shares
Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)
Management Expenses	0.07%
12b-1 Distribution Fee	none
Other Expenses	0.04%
Total Annual Fund Operating Expenses	0.11%
Vanguard Extended Duration Treasury Index Fund - Institutional Plus Shares
Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)
Management Expenses	0.04%
12b-1 Distribution Fee	none
Other Expenses	0.04%
Total Annual Fund Operating Expenses	0.08%

Distribution [and/or Service] (12b-1) Fees" include all distribution or other expenses incurred during the most recent fiscal year under a plan adopted pursuant to rule 12b-1 [17 CFR 270.12b-1]. Under an appropriate caption or a subcaption of "Other Expenses," disclose the amount of any distribution or similar expenses deducted from the Fund's assets other than pursuant to a rule 12b-1 plan.

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Management Fees include investment advisory fees (including any fees based on the Fund's performance), any other management fees payable to the investment adviser or its affiliates, and administrative fees payable to the investment adviser or its affiliates that are not included as "Other Expenses."

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Total Annual Fund Operating Expenses.

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"Other Expenses" include all expenses not otherwise disclosed in the table that are deducted from the Fund's assets or charged to all shareholder accounts. The amount of expenses deducted from the Fund's assets are the amounts shown as expenses in the Fund's statement of operations (including increases resulting from complying with paragraph 2(g) of rule 6-07 of Regulation S-X [17 CFR 210.6-07]). "Other Expenses" do not include extraordinary expenses as determined under generally accepted accounting principles (see Accounting Principles Board Opinion No. 30). If extraordinary expenses were incurred that materially affected the Fund's "Other Expenses," disclose in a footnote to the table what "Other Expenses" would have been had the extraordinary expenses been included.

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