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
Institutional | Vanguard Inflation-Protected Securities Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading <span style="color:#000000;font-family:Arial;font-size:13pt;font-weight:bold;">Fund 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 inflation protection and income consistent with investment in inflation-indexed securities.
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 Institutional 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 28% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 28.00%
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’s Institutional Shares with the cost of investing in other mutual 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 shares provide 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 redeem your investment at the end of the given period. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
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 at least 80% of its assets in inflation-indexed bonds issued by the U.S. government, its agencies and instrumentalities, and corporations. The Fund may invest in bonds of any maturity; however, its dollar-weighted average maturity is expected to be in the range of 7 to 20 years. At a minimum, all bonds purchased by the Fund will be rated investment-grade or, if unrated, will be considered by the advisor to be investment-grade.
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 An investment in the Fund could lose money over short or long periods of time.You should expect the Fund's share price and total return to fluctuate within a wide range. 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:• Interest rate risk, which is the chance that the value of a bond will fluctuate because of a change in the level of interest rates. Although inflation-indexed bonds seek to provide inflation protection, their prices may decline when interest rates rise and vice versa. Because the Fund’s dollar-weighted average maturity is expected to be in the range of 7 to 20 years, interest rate risk is expected to be moderate to high for the Fund.• Income fluctuations. The Fund’s quarterly income distributions are likely to fluctuate considerably more than the income distributions of a typical bond fund. In fact, under certain conditions, the Fund may not have any income to distribute. Income fluctuations associated with changes in interest rates are expected to be low; however, income fluctuations associated with changes in inflation are expected to be high. Overall, investors can expect income fluctuations to be high for the Fund.• 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.• 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.• Derivatives risk. The Fund may invest in derivatives, which may involve risks different from, and possibly greater than, those of investments directly in the underlying securities or assets.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 Lose Money [Text] rr_RiskLoseMoney <span style="color:#000000;font-family:Arial;font-size:9.5pt;">An investment in the Fund could lose money over short or long periods of time.</span>
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 how the performance of the Fund's Institutional Shares has varied from one calendar year to another over the periods shown. The table shows how the average annual total returns of the Institutional Shares compare with those of a relevant market 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="color:#000000;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. The bar chart shows how the performance of the Fund's Institutional Shares has varied from one calendar year to another over the periods shown. The table shows how the average annual total returns of the Institutional Shares compare with those of a relevant market index and another comparative index, which have investment characteristics similar to those of the Fund.</span>
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone <span style="color:#000000;font-family:Arial;font-size:9.5pt;">800-662-7447</span>
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress <span style="color:#000000;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="color:#000000;font-family:Arial;font-size:9.5pt;"> Keep in mind that the Fund's past performance (before and after taxes) </span><span style="color:#000000;font-family:Arial;font-size:9.5pt;">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 Inflation-Protected Securities Fund Institutional Shares</span>
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock During the periods shown in the bar chart, the highest and lowest returns for a calendar quarter were:
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="color:#000000;font-family:Arial;font-size:9.5pt;">When after-tax returns are calculated, it is </span><span style="color:#000000;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="color:#000000;font-family:Arial;font-size:9.5pt;">Please note that after-tax returns are not relevant for a shareholder </span><span style="color:#000000;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="color:#000000;font-family:Arial;font-size:9.5pt;">Also, figures captioned </span><span style="color:#000000;font-family:Arial;font-size:9.5pt;font-style:italic;">Return After Taxes on Distributions and Sale of Fund Shares</span><span style="color:#000000;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.
Institutional | Vanguard Inflation-Protected Securities Fund | Institutional Shares  
Risk Return Abstract rr_RiskReturnAbstract  
Purchase Fee rr_MaximumCumulativeSalesChargeOverOther none
Sales Charge (Load) Imposed on Purchases rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Sales Charge (Load) Imposed on Reinvested Dividends rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther none
Redemption Fee rr_RedemptionFeeOverRedemption none
Management Fees rr_ManagementFeesOverAssets 0.06%
12b-1 Distribution Fee rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.01%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.07%
1 Year rr_ExpenseExampleYear01 $ 7
3 Years rr_ExpenseExampleYear03 23
5 Years rr_ExpenseExampleYear05 40
10 Years rr_ExpenseExampleYear10 $ 90
2013 rr_AnnualReturn2013 (8.83%)
2014 rr_AnnualReturn2014 4.07%
2015 rr_AnnualReturn2015 (1.67%)
2016 rr_AnnualReturn2016 4.63%
2017 rr_AnnualReturn2017 2.97%
2018 rr_AnnualReturn2018 (1.40%)
2019 rr_AnnualReturn2019 8.18%
2020 rr_AnnualReturn2020 11.05%
2021 rr_AnnualReturn2021 5.72%
Annual Return 2022 rr_AnnualReturn2022 (11.90%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel <span style="color:#000000;font-family:Arial;font-size:8pt;margin-left:0.0pt;">Highest</span>
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2016
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 4.58%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel <span style="color:#000000;font-family:Arial;font-size:8pt;margin-left:0.0pt;">Lowest</span>
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Jun. 30, 2013
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (7.35%)
1 Year rr_AverageAnnualReturnYear01 (11.90%)
5 Years rr_AverageAnnualReturnYear05 1.98%
10 Years rr_AverageAnnualReturnYear10 1.04%
Institutional | Vanguard Inflation-Protected Securities Fund | Return After Taxes on Distributions | Institutional Shares  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (14.70%)
5 Years rr_AverageAnnualReturnYear05 0.35%
10 Years rr_AverageAnnualReturnYear10 (0.20%)
Institutional | Vanguard Inflation-Protected Securities Fund | Return After Taxes on Distributions and Sale of Fund Shares | Institutional Shares  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (7.01%)
5 Years rr_AverageAnnualReturnYear05 0.87%
10 Years rr_AverageAnnualReturnYear10 0.27%
Institutional | Vanguard Inflation-Protected Securities Fund | Bloomberg U.S. Treasury Inflation Protected Securities Index (reflects no deduction for fees, expenses, or taxes)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (11.85%)
5 Years rr_AverageAnnualReturnYear05 2.11%
10 Years rr_AverageAnnualReturnYear10 1.12%
Institutional | Vanguard Inflation-Protected Securities Fund | 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%)
5 Years rr_AverageAnnualReturnYear05 0.02%
10 Years rr_AverageAnnualReturnYear10 1.06%