| Label | Element | Value |
|---|---|---|
| Risk Return Abstract | rr_RiskReturnAbstract | |
| Registrant Name | dei_EntityRegistrantName | Vanguard Bond Index Funds |
| Prospectus Date | rr_ProspectusDate | Apr. 28, 2023 |
| Retail | 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 Investor Shares or Admiral 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 examples, 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;">Examples</span> |
| Expense Example Narrative [Text Block] | rr_ExpenseExampleNarrativeTextBlock | The following examples are intended to help you compare the cost of investing in the Fund’s Investor Shares or Admiral Shares with the cost of investing in other mutual funds. They illustrate the hypothetical expenses that you would incur over various periods if you were to invest $10,000 in the Fund's shares. These examples assume 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 Investor Shares has varied from one calendar year to another over the periods shown. The table shows how the average annual total returns of the share classes presented 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 Investor Shares has varied from one calendar year to another over the periods shown. The table shows how the average annual total returns of the share classes presented 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 Investor 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;">not relevant for a </span><span style="color:#000000;font-family:Arial;font-size:9.5pt;">shareholder who holds fund shares in a tax-deferred account, such as an individual retirement account or a 401(k) plan. </span> |
| Performance Table One Class of after Tax Shown [Text] | rr_PerformanceTableOneClassOfAfterTaxShown | <span style="color:#000000;font-family:Arial;font-size:9.5pt;">Please note that after-tax returns are shown only for the Investor </span><span style="color:#000000;font-family:Arial;font-size:9.5pt;">Shares and may differ for each share class. After-tax returns are </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 </span><span style="color:#000000;font-family:Arial;font-size:9.5pt;font-style:italic;">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 shown only for the Investor Shares and may differ for each share class. 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. |
| Retail | Vanguard Inflation-Protected Securities Fund | Investor 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 |
| Account Service Fee Per Year (for certain fund account balances below $1,000,000) | rr_MaximumAccountFee | $ 20 |
| Management Fees | rr_ManagementFeesOverAssets | 0.19% |
| 12b-1 Distribution Fee | rr_DistributionAndService12b1FeesOverAssets | none |
| Other Expenses | rr_OtherExpensesOverAssets | 0.01% |
| Total Annual Fund Operating Expenses | rr_ExpensesOverAssets | 0.20% |
| 1 Year | rr_ExpenseExampleYear01 | $ 20 |
| 3 Years | rr_ExpenseExampleYear03 | 64 |
| 5 Years | rr_ExpenseExampleYear05 | 113 |
| 10 Years | rr_ExpenseExampleYear10 | $ 255 |
| 2013 | rr_AnnualReturn2013 | (8.92%) |
| 2014 | rr_AnnualReturn2014 | 3.83% |
| 2015 | rr_AnnualReturn2015 | (1.83%) |
| 2016 | rr_AnnualReturn2016 | 4.52% |
| 2017 | rr_AnnualReturn2017 | 2.81% |
| 2018 | rr_AnnualReturn2018 | (1.49%) |
| 2019 | rr_AnnualReturn2019 | 8.06% |
| 2020 | rr_AnnualReturn2020 | 10.90% |
| 2021 | rr_AnnualReturn2021 | 5.56% |
| Annual Return 2022 | rr_AnnualReturn2022 | (11.95%) |
| 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 | 4.60% |
| 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 | (7.34%) |
| 1 Year | rr_AverageAnnualReturnYear01 | (11.95%) |
| 5 Years | rr_AverageAnnualReturnYear05 | 1.87% |
| 10 Years | rr_AverageAnnualReturnYear10 | 0.91% |
| Retail | Vanguard Inflation-Protected Securities Fund | Admiral 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 |
| Account Service Fee Per Year (for certain fund account balances below $1,000,000) | rr_MaximumAccountFee | $ 20 |
| 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 |
| 1 Year | rr_AverageAnnualReturnYear01 | (11.85%) |
| 5 Years | rr_AverageAnnualReturnYear05 | 1.97% |
| 10 Years | rr_AverageAnnualReturnYear10 | 1.01% |
| Retail | Vanguard Inflation-Protected Securities Fund | Return After Taxes on Distributions | Investor Shares | ||
| Risk Return Abstract | rr_RiskReturnAbstract | |
| 1 Year | rr_AverageAnnualReturnYear01 | (14.69%) |
| 5 Years | rr_AverageAnnualReturnYear05 | 0.29% |
| 10 Years | rr_AverageAnnualReturnYear10 | (0.27%) |
| Retail | Vanguard Inflation-Protected Securities Fund | Return After Taxes on Distributions and Sale of Fund Shares | Investor Shares | ||
| Risk Return Abstract | rr_RiskReturnAbstract | |
| 1 Year | rr_AverageAnnualReturnYear01 | (7.03%) |
| 5 Years | rr_AverageAnnualReturnYear05 | 0.80% |
| 10 Years | rr_AverageAnnualReturnYear10 | 0.20% |
| Retail | 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% |
| Retail | 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% |