Prospectus: Risk/Return: Legal Entity Identifier Document Type Document Period End Date Registrant Name Central Index Key Amendment Flag Amendment Description Trading Symbol Document Creation Date Document Effective Date Prospectus Date Document [Axis] Prospectus Retail. Retail [Member] Retail Performance Measure [Axis] Before Taxes After Taxes on Distributions Based on NAV Return After Taxes on Distributions Return After Taxes on Distributions After Taxes on Distributions and Sales Based on NAV Return After Taxes on Distributions and Sale of Fund Shares Return After Taxes on Distributions and Sale of Fund Shares Series [Axis] Series S000002841 [Member] Vanguard Extended Market Index Fund Vanguard Extended Market Index Fund Member Share Class [Axis] Share Classes C000007780 [Member] Admiral Shares Admiral Shares,Vanguard Extended Market Index Fund Member C000007779 [Member] Investor Shares Investor Shares,Vanguard Extended Market Index Fund Member Risk/Return [Heading] Objective [Heading] Objective, Primary [Text Block] Objective, Secondary [Text Block] Expense [Heading] Expense Narrative [Text Block] Shareholder Fees Caption [Text] Shareholder Fees [Table] Operating Expenses Caption [Text] Annual Fund Operating Expenses [Table] Expense Footnotes [Text Block] Expenses Deferred Charges [Text Block] Expenses Range of Exchange Fees [Text Block] Expense Example [Heading] Expense Example by Year [Heading] Expense Example Narrative [Text Block] Expense Example by, Year, Caption [Text] Expense Example, With Redemption [Table] Expense Example, No Redemption Narrative [Text Block] Expense Example, No Redemption, By Year, Caption [Text] Expense Example, No Redemption [Table] Expense Example Footnotes [Text Block] Expense Example Closing [Text Block] Portfolio Turnover [Heading] Portfolio Turnover [Text Block] Strategy [Heading] Strategy Narrative [Text Block] Risk [Heading] Risk Narrative [Text Block] Risk Footnotes [Text Block] Risk Closing [Text Block] Bar Chart and Performance Table [Heading] Performance Narrative [Text Block] Bar Chart Narrative [Text Block] Bar Chart [Heading] Bar Chart [Table] Bar Chart Footnotes [Text Block] Bar Chart Closing [Text Block] Performance Table Heading Performance [Table] Performance Table Narrative Market Index Performance [Table] Performance Table Footnotes Performance Table Closing [Text Block] Shareholder Fees: Sales Charge (Load) Imposed on Purchases Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) Purchase Fee Maximum Cumulative Sales Charge (as a percentage) Sales Charge (Load) Imposed on Reinvested Dividends Maximum Sales Charge on Reinvested Dividends and Distributions (as a percentage) Redemption Fee Redemption Fee (as a percentage of Amount Redeemed) Account Service Fee (for certain fund account balances below $10,000) Exchange Fee Account Service Fee (for certain fund account balances below $10,000) Maximum Account Fee Shareholder Fees Column [Text] Maximum Cumulative Sales Charge (as a percentage of Offering Price) Maximum Deferred Sales Charge (as a percentage of Offering Price) Maximum Deferred Sales Charge (as a percentage) Redemption Fee Redemption Fee Exchange Fee (as a percentage of Amount Redeemed) Maximum Account Fee (as a percentage of Assets) Shareholder Fee, Other Net Expenses (as a percentage of Assets) Net Expenses Expenses (as a percentage of Assets) Total Annual Fund Operating Expenses Total Annual Fund Operating Expenses Management Fees (as a percentage of Assets) Management Fees Distribution and Service (12b-1) Fees 12b-1 Distribution Fee Distribution or Similar (Non 12b-1) Fees Component1 Other Expenses Component2 Other Expenses Component3 Other Expenses Other Expenses (as a percentage of Assets): Other Expenses Acquired Fund Fees and Expenses Fee Waiver or Reimbursement Fee Waiver or Reimbursement Operating Expenses: Operating Expenses Column [Text] Expense Example: 1 Year Expense Example, with Redemption, 1 Year 3 Years Expense Example, with Redemption, 3 Years 5 Years Expense Example, with Redemption, 5 Years 10 Years Expense Example, with Redemption, 10 Years Expense Example, By Year, Column [Text] Column Bar Chart Table: Annual Return Caption [Text] Caption Annual Return, Column [Text] Column Annual Return, Inception Date Inception Date Annual Return 1990 Annual Return 1991 Annual Return 1992 Annual Return 1993 Annual Return 1994 Annual Return 1995 Annual Return 1996 Annual Return 1997 Annual Return 1998 Annual Return 1999 Annual Return 2000 Annual Return 2001 Annual Return 2002 Annual Return 2003 Annual Return 2004 Annual Return 2005 Annual Return 2006 2006 Annual Return 2007 2007 Annual Return 2008 2008 Annual Return 2009 2009 Annual Return 2010 2010 Annual Return 2011 2011 Annual Return 2012 2012 Annual Return 2013 2013 Annual Return 2014 2014 Annual Return 2015 2015 Annual Return 2016 Annual Return 2017 Annual Return 2018 Annual Return 2019 Annual Return 2020 Standard & Poor's Completion Index Standard And Poors Completion Index [Member] Standard & Poor's Completion Index Spliced Dow Jones U.S. Completion Total Stock Market Index. Spliced Dow Jones Us Completion Total Stock Market Index [Member] Spliced Dow Jones U.S. Completion Total Stock Market Index Average Annual Return: 1 Year 1 Year 5 Years 5 Years 10 Years 10 Years Label Since Inception Since Inception Inception Date Inception Date Risk/Return Detail [Table] 1 Year Expense Example, No Redemption, 1 Year 3 Years Expense Example, No Redemption, 3 Years 5 Years Expense Example, No Redemption, 5 Years 10 Years Expense Example, No Redemption, 10 Years Fee Waiver or Reimbursement over Assets, Date of Termination Portfolio Turnover, Rate Expense Breakpoint Discounts [Text] Expense Breakpoint, Minimum Investment Required [Amount] Expense Exchange Traded Fund Commissions [Text] Expenses Represent Both Master and Feeder [Text] Expenses Explanation of Nonrecurring Account Fee [Text] Other Expenses, New Fund, Based on Estimates [Text] Acquired Fund Fees and Expenses, Based on Estimates [Text] Expenses Other Expenses Had Extraordinary Expenses Been Included [Text] Expenses Restated to Reflect Current [Text] Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text] Strategy Portfolio Concentration [Text] Risk Lose Money [Text] Risk Nondiversified Status [Text] Risk Money Market Fund [Text]