v3.23.1
Label Element Value
Risk Return Abstract rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName Vanguard Bond Index Funds
Prospectus Date rr_ProspectusDate Apr. 28, 2023
ETF | Vanguard Ultra-Short Bond ETF  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading <span style="color:#000000;font-family:Arial;font-size:13pt;font-weight:bold;">ETF Summary</span>
Objective [Heading] rr_ObjectiveHeading <span style="color:#000000;font-family:Arial;font-size:10pt;font-weight:bold;">Investment Objective</span>
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The Fund seeks to provide current income while maintaining limited price volatility.
Expense [Heading] rr_ExpenseHeading <span style="color:#000000;font-family:Arial;font-size:10pt;font-weight:bold;">Fees and Expenses</span>
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy, hold, and sell shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the table and example below.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption <span style="color:#000000;font-family:Arial;font-size:8.5pt;font-weight:bold;">Shareholder Fees</span> <br/><span style="color:#000000;font-family:Arial;font-size:8.5pt;margin-left:0%;">(Fees paid directly from your investment)</span>
Operating Expenses Caption [Text] rr_OperatingExpensesCaption <span style="color:#000000;font-family:Arial;font-size:8.5pt;font-weight:bold;">Annual Fund Operating Expenses</span> <br/><span style="color:#000000;font-family:Arial;font-size:8.5pt;margin-left:0%;">(Expenses that you pay each year as a percentage of the value of your investment)</span>
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading <span style="color:#000000;font-family:Arial;font-size:9.5pt;">Portfolio Turnover</span>
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in more taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the previous expense example, reduce the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 73% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 73.00%
Expense Example [Heading] rr_ExpenseExampleHeading <span style="color:#000000;font-family:Arial;font-size:9.5pt;">Example</span>
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following example is intended to help you compare the cost of investing in the Fund with the cost of investing in other funds. It illustrates the hypothetical expenses that you would incur over various periods if you were to invest $10,000 in the Fund's shares. This example assumes that the Fund provides a return of 5% each year and that total annual fund operating expenses remain as stated in the preceding table. You would incur these hypothetical expenses whether or not you were to sell your shares at the end of the given period. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example Closing [Text Block] rr_ExpenseExampleClosingTextBlock This example does not include the brokerage commissions that you may pay to buy and sell Shares of the Fund.
Strategy [Heading] rr_StrategyHeading <span style="color:#000000;font-family:Arial;font-size:10pt;font-weight:bold;">Principal Investment Strategies</span>
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock The Fund invests in a diversified portfolio of high-quality and, to a lesser extent, medium-quality fixed income securities. High-quality fixed income securities are investment-grade securities that are rated the equivalent of A3 or better by Moody‘s Investors Service, Inc. (Moody‘s) or another independent rating agency or, if unrated, are determined to be of comparable quality by the Fund’s advisor. Medium-quality fixed income securities are investment-grade securities that are rated the equivalent of Baa1, Baa2, or Baa3 by Moody‘s or another independent rating agency or, if unrated, are determined to be of comparable quality by the Fund’s advisor. The Fund is expected to maintain a dollar-weighted average maturity of 0 to 2 years. Under normal circumstances, the Fund will invest at least 80% of its assets in fixed income securities.
Risk [Heading] rr_RiskHeading <span style="color:#000000;font-family:Arial;font-size:10pt;font-weight:bold;">Principal Risks</span>
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock The Fund is designed for investors with a low tolerance for risk, but you could still lose money by investing in it. The Fund is subject to the following risks, which could affect the Fund's performance, and the level of risk may vary based on market conditions:• Income risk, which is the chance that the Fund's income will decline because of falling interest rates. Income risk is generally high for short-term bond funds, so investors should expect the Fund’s monthly income to fluctuate accordingly.• Interest rate risk, which is the chance that bond prices overall will decline because of rising interest rates.• Credit risk, which is the chance that a bond issuer will fail to pay interest or principal in a timely manner or that negative perceptions of the issuer’s ability to make such payments will cause the price of that bond to decline.• Liquidity risk, which is the chance that the Fund may not be able to sell a security in a timely manner at a desired price.• Call risk, which is the chance that during periods of falling interest rates, issuers of callable bonds may call (redeem) securities with higher coupon rates or interest rates before their maturity dates. The Fund would then lose any price appreciation above the bond’s call price and would be forced to reinvest the unanticipated proceeds at lower interest rates, resulting in a decline in the Fund’s income.• Prepayment risk, which is the chance that during periods of falling interest rates, homeowners will refinance their mortgages before their maturity dates, resulting in prepayment of mortgage-backed securities held by the Fund. The Fund would then lose any price appreciation above the mortgage’s principal and would be forced to reinvest the unanticipated proceeds at lower interest rates, resulting in a decline in the Fund's income. Such prepayments and subsequent reinvestments would also increase the Fund’s portfolio turnover rate.• Manager risk, which is the chance that poor security selection will cause the Fund to underperform relevant benchmarks or other funds with a similar investment objective.• Derivatives risk. The Fund may invest in derivatives. In general, investments in derivatives may involve risks different from, and possibly greater than, those of investments directly in the underlying securities or assets.Because the Fund is an exchange-traded fund (ETF) and the Fund's shares are traded on an exchange, the Fund is subject to additional risks:• The Fund’s ETF Shares are listed for trading on Cboe BZX Exchange, Inc. and are bought and sold on the secondary market at market prices. Although it is expected that the market price of an ETF Share typically will approximate its net asset value (NAV), there may be times when the market price and the NAV differ significantly. Thus, you may pay more or less than NAV when you buy ETF Shares on the secondary market, and you may receive more or less than NAV when you sell those shares.• Although the Fund’s ETF Shares are listed for trading on Cboe BZX Exchange, Inc., it is possible that an active trading market may not be maintained, which could increase the Fund’s risks as disclosed in this prospectus.• Trading of the Fund’s ETF Shares may be halted by the activation of individual or marketwide trading halts (which halt trading for a specific period of time when the price of a particular security or overall market prices decline by a specified percentage). Trading of the Fund’s ETF Shares may also be halted if (1) the shares are delisted from Cboe BZX Exchange, Inc. without first being listed on another exchange or (2) Cboe BZX Exchange, Inc. officials determine that such action is appropriate in the interest of a fair and orderly market or for the protection of investors.An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution <span style="color:#000000;font-family:Arial;font-size:9.5pt;font-weight:bold;">An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.</span>
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading <span style="color:#000000;font-family:Arial;font-size:10pt;font-weight:bold;">Annual Total Returns</span>
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The following bar chart and table are intended to help you understand the risks of investing in the Fund. The bar chart shows the performance of the Fund's ETF Shares (based on NAV) in their first calendar year. The table shows how the average annual total returns of the ETF shares compare with those of the Fund’s target index and another comparative index, which have investment characteristics similar to those of the Fund. Keep in mind that the Fund's past performance (before and after taxes) does not indicate how the Fund will perform in the future. Updated performance information is available on our website at vanguard.com/performance or by calling Vanguard toll-free at 800-662-7447.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns <span style="font-family:Arial;font-size:9.5pt;">The following bar chart and table are intended to help you understand the risks of investing in the Fund.</span><span style="font-family:Arial;font-size:9.5pt;line-height:11.5pt;"> </span><span style="font-family:Arial;font-size:9.5pt;">The bar chart shows the performance of the Fund's ETF Shares</span><span style="font-family:Arial;font-size:9.5pt;line-height:11.5pt;"> </span><span style="font-family:Arial;font-size:9.5pt;"> (based on NAV) in their first calendar year.</span><span style="font-family:Arial;font-size:9.5pt;line-height:11.5pt;"> </span><span style="font-family:Arial;font-size:9.5pt;">The</span><span style="font-family:Arial;font-size:9.5pt;line-height:11.5pt;"> </span><span style="font-family:Arial;font-size:9.5pt;">table shows how the average annual total returns of the ETF shares compare with those of the Fund’s target index and another comparative index, which have investment characteristics similar to those of the Fund.</span>
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone <span style="font-family:Arial;font-size:9.5pt;">800-662-7447</span>
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress <span style="font-family:Arial;font-size:9.5pt;font-style:italic;">vanguard.com/performance</span>
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture <span style="font-family:Arial;font-size:9.5pt;"> Keep in mind that the Fund's past performance (before and after taxes) does not indicate how the Fund will perform in the future.</span>
Bar Chart [Heading] rr_BarChartHeading <span style="font-family:Arial;font-size:8pt;font-weight:bold;">Annual Total Returns — Vanguard Ultra-Short Bond ETF Shares</span>
Performance Table Heading rr_PerformanceTableHeading <span style="font-family:Arial;font-size:8.5pt;font-weight:bold;">Average Annual Total Returns for Periods Ended December 31, 2022</span>
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate <span style="font-family:Arial;font-size:9.5pt;">When after-tax returns are calculated, it is </span><span style="font-family:Arial;font-size:9.5pt;">assumed that the shareholder was in the highest individual federal marginal income tax bracket at the time of each distribution of income or capital gains or upon redemption. State and local income taxes are not reflected in the calculations. </span>
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred <span style="font-family:Arial;font-size:9.5pt;">Please note that after-tax returns are not relevant for a shareholder </span><span style="font-family:Arial;font-size:9.5pt;">who holds fund shares in a tax-deferred account, such as an individual retirement account or a 401(k) plan. </span>
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher <span style="font-family:Arial;font-size:9.5pt;">Also, figures captioned </span><span style="font-family:Arial;font-size:9.5pt;font-style:italic;">Return After Taxes on Distributions and Sale of Fund Shares</span><span style="font-family:Arial;font-size:9.5pt;"> may be higher than other figures for the same period if a capital loss occurs upon redemption and results in an assumed tax deduction for the shareholder.</span>
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock Actual after-tax returns depend on your tax situation and may differ from those shown in the preceding table. When after-tax returns are calculated, it is assumed that the shareholder was in the highest individual federal marginal income tax bracket at the time of each distribution of income or capital gains or upon redemption. State and local income taxes are not reflected in the calculations. Please note that after-tax returns are not relevant for a shareholder who holds fund shares in a tax-deferred account, such as an individual retirement account or a 401(k) plan. Also, figures captioned Return After Taxes on Distributions and Sale of Fund Shares may be higher than other figures for the same period if a capital loss occurs upon redemption and results in an assumed tax deduction for the shareholder.
ETF | Vanguard Ultra-Short Bond ETF | ETF Shares  
Risk Return Abstract rr_RiskReturnAbstract  
Management Fees rr_ManagementFeesOverAssets 0.09%
12b-1 Distribution Fee rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.01%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.10%
1 Year rr_ExpenseExampleYear01 $ 10
3 Years rr_ExpenseExampleYear03 32
5 Years rr_ExpenseExampleYear05 56
10 Years rr_ExpenseExampleYear10 $ 128
2022 rr_AnnualReturn2022 (0.43%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel <span style="font-family:Arial;font-size:8pt;margin-left:0.0pt;">Highest</span>
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Dec. 31, 2022
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 0.89%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel <span style="font-family:Arial;font-size:8pt;margin-left:0.0pt;">Lowest</span>
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2022
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (1.02%)
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 05, 2021
Transaction Fee on Purchases and Sales bondindex_TransactionFeeOnPurchasesandSales none [1]
Transaction Fee on Reinvested Dividends bondindex_TransactionFeeOnReinvestedDividends none [1]
ETF | Vanguard Ultra-Short Bond ETF | Based on NAV | ETF Shares  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (0.43%)
Since Fund Inception rr_AverageAnnualReturnSinceInception (0.18%)
ETF | Vanguard Ultra-Short Bond ETF | Based on Market Price | ETF Shares  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (0.39%)
Since Fund Inception rr_AverageAnnualReturnSinceInception (0.12%)
ETF | Vanguard Ultra-Short Bond ETF | Bloomberg U.S. Aggregate Bond Index (reflects no deduction for fees, expenses, or taxes)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (13.01%)
Since Fund Inception rr_AverageAnnualReturnSinceInception (6.81%)
ETF | Vanguard Ultra-Short Bond ETF | Based on NAV Return After Taxes on Distributions | ETF Shares  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (1.06%)
Since Fund Inception rr_AverageAnnualReturnSinceInception (0.60%)
ETF | Vanguard Ultra-Short Bond ETF | Based on NAV Return After Taxes on Distributions and Sale of Fund Shares | ETF Shares  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (0.25%)
Since Fund Inception rr_AverageAnnualReturnSinceInception (0.31%)
ETF | Vanguard Ultra-Short Bond ETF | Bloomberg U.S. Treasury Bellwethers: 1 Year Index (reflects no deduction for fees, expenses, or taxes)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (0.12%)
Since Fund Inception rr_AverageAnnualReturnSinceInception (0.09%)
[1] None through Vanguard (Broker fees vary)