v3.24.1.1.u2
Label Element Value
Risk Return Abstract rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName Vanguard Fixed Income Securities Funds
Prospectus Date rr_ProspectusDate May 24, 2024
Institutional | Vanguard Short-Term Investment-Grade 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 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 tables describe 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 tables 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 70% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 70.00%
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 in a variety of high-quality and medium-quality fixed income securities, at least 80% of which will be short- and intermediate-term investment-grade securities. High-quality fixed income securities are those 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 those 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. Investment-grade fixed income securities are those rated the equivalent of Baa3 and above 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 1 to 4 years. The Fund may invest in derivatives instruments, such as options, futures contracts, and other swap agreements.
Risk [Heading] rr_RiskHeading <span style="color:#000000;font-family:Arial;font-size:10pt;font-weight:bold;">Principal Risks</span>
Risk [Text Block] rr_RiskTextBlock • 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. Interest rate risk should be low for the Fund because it invests primarily in short-term bonds, whose prices are less sensitive to interest rate changes than are the prices of longer-term bonds.• 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. Credit risk should be low to moderate for the Fund because it invests primarily in bonds that are considered high-quality or medium-quality.• 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. Such redemptions and subsequent reinvestments would also increase the Fund’s portfolio turnover rate.• Extension risk, which is the chance that during periods of rising interest rates, certain debt securities will be paid off substantially more slowly than originally anticipated, and the value of those securities may fall.• 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.• 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. In addition, significant investment in the financial sector subjects the Fund to proportionately higher exposure to the risks of this sector.• 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.
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 relevant market indexes, 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. 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 relevant market indexes, 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 </span><span style="font-family:Arial;font-size:9.5pt;">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 Short-Term Investment-Grade Fund Institutional Shares</span><span style="font-family:Arial;font-size:5pt;font-weight:bold;position:relative;top:-3.25pt;">1</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, 2023</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 </span><span style="color:#000000;font-family:Arial;font-size:9.5pt;font-style:italic;">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 Short-Term Investment-Grade Fund | Risk Lose Money [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock The Fund is designed for investors with a low tolerance for risk, but you could still lose money by investing in it.
Institutional | Vanguard Short-Term Investment-Grade Fund | Risk Not Insured Depository Institution [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock 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.
Institutional | Vanguard Short-Term Investment-Grade 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
Year to Date Return, Label rr_YearToDateReturnLabel year-to-date return
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2024
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 0.68%
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 Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 4.85%
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 Mar. 31, 2022
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (3.79%)
1 Year rr_AverageAnnualReturnYear01 6.20%
5 Years rr_AverageAnnualReturnYear05 2.16%
10 Years rr_AverageAnnualReturnYear10 1.98%
Institutional | Vanguard Short-Term Investment-Grade Fund | Return After Taxes on Distributions | Institutional Shares  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 4.81%
5 Years rr_AverageAnnualReturnYear05 1.12%
10 Years rr_AverageAnnualReturnYear10 0.97%
Institutional | Vanguard Short-Term Investment-Grade Fund | Return After Taxes on Distributions and Sale of Fund Shares | Institutional Shares  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 3.64%
5 Years rr_AverageAnnualReturnYear05 1.22%
10 Years rr_AverageAnnualReturnYear10 1.08%
Institutional | Vanguard Short-Term Investment-Grade Fund | Bloomberg U.S. Aggregate Bond Index (reflects no deduction for fees, expenses, or taxes)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 5.53%
5 Years rr_AverageAnnualReturnYear05 1.10%
10 Years rr_AverageAnnualReturnYear10 1.81%
Institutional | Vanguard Short-Term Investment-Grade Fund | Bloomberg U.S. 1-5 Year Credit Bond Index (reflects no deduction for fees, expenses, or taxes)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 5.94%
5 Years rr_AverageAnnualReturnYear05 2.21%
10 Years rr_AverageAnnualReturnYear10 2.01%