Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	VANGUARD CONVERTIBLE SECURITIES FUND
Prospectus Date	rr_ProspectusDate	Mar. 29, 2016
Investor Shares for Participants | VANGUARD CONVERTIBLE SECURITIES 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 and long-term capital appreciation.
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 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 most recent fiscal year, the Fund’s portfolio turnover rate was 95% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	95.00%
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 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 Fund provides 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	Under normal circumstances, the Fund invests at least 80% of its assets in U.S. and foreign convertible securities, which are hybrid securities that combine the investment characteristics of bonds and common stocks. Convertible securities include corporate bonds and preferred stocks that are convertible into common stock, as well as fixed income securities with warrants or common stock attached. Many convertible securities have credit ratings that are below investment grade.
Risk [Heading]	rr_RiskHeading	Principal Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	An investment in the Fund could lose money over short or even long periods. 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: • Stock market risk, which is the chance that stock prices overall will decline, causing the prices of convertible securities to decline. Stock markets tend to move in cycles, with periods of rising prices and periods of falling prices. The Fund’s investments in securities that are convertible into foreign stocks may perform differently from their U.S. counterparts. • Credit risk, which is the chance that the issuer of a convertible security will fail to pay interest, dividends, 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 security to decline. Companies that issue convertible securities are often small to mid-size, and they often have credit ratings below investment grade. In addition, the credit rating of a company’s convertible securities is generally lower than that of its nonconvertible debt securities. Convertible securities are normally considered ”junior“ securities—that is, the issuer usually must make required interest and principal payments on its nonconvertible debt before it can make payments on its convertible securities. If an issuer stops making interest or principal payments, these securities may become worthless and the Fund could lose its entire investment. Reflecting the universe of convertible securities, most of the Fund’s rated holdings are below investment grade (commonly referred to as “junk bonds”), and some may be unrated. Therefore, credit risk is greater for the Fund than for funds that invest in higher-grade securities. • Interest rate risk, which is the chance that prices of convertible securities will decline along with overall bond prices because of rising interest rates. Convertible securities are more sensitive to interest rate changes when their predetermined conversion price is much higher than the price of the issuing company’s common stock, and are less sensitive to interest rate changes as the price of the issuing company’s stock approaches the predetermined conversion 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 information technology sector subjects the Fund to proportionately higher exposure to the risks of this sector. • 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. • Country/regional risk, which is the chance that world events—such as political upheaval, financial troubles, or natural disasters—will adversely affect the value and/or liquidity of securities issued by companies in foreign countries or regions. Because the Fund may invest a large portion of its assets in securities of companies located in any one country or region, the Fund’s performance may be hurt disproportionately by the poor performance of its investments in that area. • Currency hedging risk, which is the chance that the currency hedging transactions entered into by the Fund may not perfectly offset the Fund’s foreign currency exposure. For example, the Fund will decline in value if it underhedges a currency that has weakened or overhedges a currency that has strengthened relative to the U.S. dollar. 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 even long periods.
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 has varied from one calendar year to another over the periods shown. The table shows how the average annual total returns of the Fund compare with those of a relevant market index and other comparative benchmarks, which have investment characteristics similar to those of the Fund. Returns for the Convertible Securities Funds Average are derived from data provided by Lipper, a Thomson Reuters Company. Keep in mind that the Fund’s past performance 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 has varied from one calendar year to another over the periods shown. The table shows how the average annual total returns of the Fund compare with those of a relevant market index and other comparative benchmarks, which have 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 does not indicate how the Fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Annual Total Returns — Vanguard Convertible Securities Fund Investor Shares
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	During the periods shown in the bar chart, the highest return for a calendar quarter was 14.66% (quarter ended September 30, 2009), and the lowest return for a quarter was –15.90% (quarter ended December 31, 2008).
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns for Periods Ended December 31, 2015
Investor Shares for Participants | VANGUARD CONVERTIBLE SECURITIES 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	0.36%
12b-1 Distribution Fee	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.02%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.38%
1 Year	rr_ExpenseExampleYear01	$ 39
3 Years	rr_ExpenseExampleYear03	122
5 Years	rr_ExpenseExampleYear05	213
10 Years	rr_ExpenseExampleYear10	480
1 Year	rr_ExpenseExampleNoRedemptionYear01	39
3 Years	rr_ExpenseExampleNoRedemptionYear03	122
5 Years	rr_ExpenseExampleNoRedemptionYear05	213
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 480
2006	rr_AnnualReturn2006	12.94%
2007	rr_AnnualReturn2007	10.61%
2008	rr_AnnualReturn2008	(29.79%)
2009	rr_AnnualReturn2009	40.81%
2010	rr_AnnualReturn2010	19.24%
2011	rr_AnnualReturn2011	(6.75%)
2012	rr_AnnualReturn2012	14.47%
2013	rr_AnnualReturn2013	19.17%
2014	rr_AnnualReturn2014	2.38%
2015	rr_AnnualReturn2015	(1.42%)
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	14.66%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(15.90%)
1 Year	rr_AverageAnnualReturnYear01	(1.42%)
5 Years	rr_AverageAnnualReturnYear05	5.13%
10 Years	rr_AverageAnnualReturnYear10	6.58%
Investor Shares for Participants | VANGUARD CONVERTIBLE SECURITIES FUND | Bank of America Merrill Lynch All US Convertibles Index (reflects no deduction for fees or expenses)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(2.99%)	[1]
5 Years	rr_AverageAnnualReturnYear05	7.65%	[1]
10 Years	rr_AverageAnnualReturnYear10	6.68%	[1]
Investor Shares for Participants | VANGUARD CONVERTIBLE SECURITIES FUND | Convertibles Composite Index (reflects no deduction for fees or expenses)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	0.24%	[1]
5 Years	rr_AverageAnnualReturnYear05	7.08%	[1]
10 Years	rr_AverageAnnualReturnYear10	6.39%	[1]
Investor Shares for Participants | VANGUARD CONVERTIBLE SECURITIES FUND | Convertible Securities Funds Average
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(3.52%)	[1]
5 Years	rr_AverageAnnualReturnYear05	5.47%	[1]
10 Years	rr_AverageAnnualReturnYear10	5.51%	[1]

[1] Comparative Benchmarks