Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	VANGUARD SCOTTSDALE FUNDS
Prospectus Date	rr_ProspectusDate	Dec. 21, 2018
Retail | Vanguard Mortgage-Backed Securities Index Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Vanguard Mortgage-Backed Securities Index Fund
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Fund seeks to track the performance of a market-weighted mortgage-backed securities index.
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 Admiral Shares of the Fund.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees <br/><br/>(Fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses <br/><br/>(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 most recent fiscal year, the Fund’s portfolio turnover rate was 279% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	279.00%
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 Admiral 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 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 employs an indexing investment approach designed to track the performance of the Bloomberg Barclays U.S. MBS Float Adjusted Index. This Index covers U.S. agency mortgage-backed pass-through securities issued by the Government National Mortgage Association (GNMA), the Federal National Mortgage Association (FNMA), and the Federal Home Loan Mortgage Corporation (FHLMC). To be included in the Index, pool aggregates must have at least $250 million currently outstanding and a weighted average maturity of at least 1 year. The Fund invests by sampling the Index, meaning that it holds a range of securities that, in the aggregate, approximates the full Index in terms of key risk factors and other characteristics. All of the Fund’s investments will be selected through the sampling process, and under normal circumstances, at least 80% of the Fund’s assets will be invested in bonds included in the Index. The Fund maintains a dollar-weighted average maturity consistent with that of the Index. As of August 31, 2018, the dollar-weighted average maturity of the Index was 7.4 years.
Risk [Heading]	rr_RiskHeading	Principal Risks
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: • 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. Prepayment risk is high for the Fund. • Extension risk, which is the chance that during periods of rising interest rates, homeowners will repay their mortgages at slower rates. This will lengthen the duration or average life of mortgage-backed securities held by the Fund and delay the Fund’s ability to reinvest proceeds at higher interest rates. Extension risk is high for the Fund. • Interest rate risk, which is the chance that bond prices will decline because of rising interest rates. In addition, when interest rates decline, mortgage-backed securities’ prices typically do not rise as much as the prices of comparable bonds. This is because the market tends to discount mortgage-backed securities’ prices for prepayment risk when interest rates decline. Interest rate risk should be moderate for the Fund. • Income risk, which is the chance that the Fund’s income will decline because of falling interest rates. Income risk is generally moderate for intermediate-term bond funds, so investors should expect the Fund’s monthly income to fluctuate accordingly. • Credit risk, which is the chance that the issuer of a mortgage-backed security 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 very low for the Fund because it invests in securities issued by U.S. government agencies and instrumentalities, including many securities backed by the full faith and credit of the U.S. government. • Index sampling risk, which is the chance that the securities selected for the Fund, in the aggregate, will not provide investment performance matching that of the Fund‘s target index. Index sampling risk for the Fund is expected to be low. • 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. 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	An investment in the Fund could lose money over short or long periods of time.
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 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 Admiral Shares has varied from one calendar year to another over the periods shown. The table shows how the average annual total returns of the Admiral Shares compare with those of the Fund‘s target index, which has investment characteristics similar to those of the Fund. The Fund‘s Signal Shares were renamed Admiral Shares on October 16, 2013. 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	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 Admiral Shares has varied from one calendar year to another over the periods shown. The table shows how the average annual total returns of the Admiral Shares compare with those of the Fund‘s target index, which has investment characteristics similar to those of the Fund.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800-662-7447
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	vanguard.com/performance
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	Keep in mind that the Fund’s past performance (before and after taxes) does not indicate how the Fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Annual Total Returns — Vanguard Mortgage-Backed Securities Index Fund Admiral Shares
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	During the periods shown in the bar chart, the highest return for a calendar quarter was 2.76% (quarter ended June 30, 2010), and the lowest return for a quarter was –1.97% (quarter ended December 31, 2016).
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns for Periods Ended December 31, 2017
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	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.
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	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.
Performance Table Explanation after Tax Higher	rr_PerformanceTableExplanationAfterTaxHigher	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.
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	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.
Retail | Vanguard Mortgage-Backed Securities Index Fund | Admiral 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
Account Service Fee (for certain fund account balances below $10,000)	rr_MaximumAccountFee	$ 20	[1]
Management Fees	rr_ManagementFeesOverAssets	0.05%
12b-1 Distribution Fee	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.02%
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
1 Year	rr_ExpenseExampleNoRedemptionYear01	7
3 Years	rr_ExpenseExampleNoRedemptionYear03	23
5 Years	rr_ExpenseExampleNoRedemptionYear05	40
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 90
2010	rr_AnnualReturn2010	5.23%	[2]
2011	rr_AnnualReturn2011	5.88%	[2]
2012	rr_AnnualReturn2012	2.54%	[2]
2013	rr_AnnualReturn2013	(1.29%)	[2]
2014	rr_AnnualReturn2014	5.77%	[2]
2015	rr_AnnualReturn2015	1.44%	[2]
2016	rr_AnnualReturn2016	1.47%	[2]
2017	rr_AnnualReturn2017	2.32%	[2]
Year to Date Return, Label	rr_YearToDateReturnLabel	year-to-date return
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2018
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	(1.09%)
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2010
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	2.76%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2016
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(1.97%)
1 Year	rr_AverageAnnualReturnYear01	2.32%
5 Years	rr_AverageAnnualReturnYear05	1.92%
Since Inception	rr_AverageAnnualReturnSinceInception	2.76%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 03, 2009
Retail | Vanguard Mortgage-Backed Securities Index Fund | Return After Taxes on Distributions | Admiral Shares
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	1.37%
5 Years	rr_AverageAnnualReturnYear05	1.12%
Since Inception	rr_AverageAnnualReturnSinceInception	1.90%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 03, 2009
Retail | Vanguard Mortgage-Backed Securities Index Fund | Return After Taxes on Distributions and Sale of Fund Shares | Admiral Shares
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	1.31%
5 Years	rr_AverageAnnualReturnYear05	1.10%
Since Inception	rr_AverageAnnualReturnSinceInception	1.77%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 03, 2009
Retail | Vanguard Mortgage-Backed Securities Index Fund | Bloomberg Barclays U.S. MBS Float Adjusted Index (reflects no deduction for fees, expenses, or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	2.37%
5 Years	rr_AverageAnnualReturnYear05	2.00%
Since Inception	rr_AverageAnnualReturnSinceInception	2.82%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 03, 2009

[1] /year

[2] The year-to-date return as of the most recent calendar quarter, which ended on September 30, 2018, was –1.09%.