Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	VANGUARD FIXED INCOME SECURITIES FUNDS
Prospectus Date	rr_ProspectusDate	May 26, 2016
Investor Shares for Participants | Vanguard Ultra-Short-Term Bond Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Fund Summary
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Fund seeks to provide current income while maintaining limited price volatility.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	The following table describes the fees and expenses you may pay if you buy and hold Investor Shares of the Fund.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (Fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (Expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover
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 fiscal period from February 24, 2015, to January 31, 2016, the Fund’s portfolio turnover rate was 24% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	24.00%
Expense Example [Heading]	rr_ExpenseExampleHeading	Example
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following example is intended to help you compare the cost of investing in the Fund’s Investor Shares with the cost of investing in other mutual funds. It illustrates the hypothetical expenses that you would incur over various periods if you invested $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 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	Principal Investment Strategies
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 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. The Fund may invest no more than 30% of its assets in medium-quality fixed income securities. 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	Principal Risks
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: • 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. • Interest rate risk, which is the chance that bond prices 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 for the Fund because it invests primarily in bonds that are considered high-quality. • 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. Liquidity risk should be low for the Fund, because it invests only a portion of its assets in corporate bonds. • 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, 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	The Fund is designed for investors with a low tolerance for risk, but you could still lose money by investing in it.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	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.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Annual Total Returns
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The Fund has not been in operation long enough to report a full calendar-year return. Performance information is available on our website at vanguard.com/performance or by calling Vanguard toll-free at 800-662-7447.
Performance One Year or Less [Text]	rr_PerformanceOneYearOrLess	The Fund has not been in operation long enough to report a full calendar-year return.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800-662-7447
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	vanguard.com/performance
Investor Shares for Participants | Vanguard Ultra-Short-Term Bond Fund | Investor Shares
Risk/Return:	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	0.17%
12b-1 Distribution Fee	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.03%
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
1 Year	rr_ExpenseExampleNoRedemptionYear01	20
3 Years	rr_ExpenseExampleNoRedemptionYear03	64
5 Years	rr_ExpenseExampleNoRedemptionYear05	113
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 255