<?xml version="1.0" encoding="utf-8"?>
<FilingSummary xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <Version>2.4.1.9</Version>
  <ProcessingTime />
  <ReportFormat>Html</ReportFormat>
  <ContextCount>15</ContextCount>
  <ElementCount>82</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>9</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>2</UnitCount>
  <MyReports>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>020060 - Schedule - Average Annual Total Returns {Transposed}</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/rr/role/PerformanceTableData</Role>
      <ShortName>Average Annual Total Returns</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>030000 - Document - Risk/Return Detail {Unlabeled}</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/rr/role/RiskReturnDetail</Role>
      <ShortName>Risk/Return Detail</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>2711587 - Schedule - Average Annual Total Returns (Vanguard Convertible Securities Fund Retail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://vanguard/role/S000002837PerformanceTableDataRetail</Role>
      <ShortName>Average Annual Total Returns (Vanguard Convertible Securities Fund Retail)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>2711588 - Schedule - Average Annual Total Returns (Vanguard Convertible Securities Fund Participant)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://vanguard/role/S000002837PerformanceTableDataParticipant</Role>
      <ShortName>Average Annual Total Returns (Vanguard Convertible Securities Fund Participant)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>2711900 - Schedule - Expense Example, No Redemption {Transposed} (Vanguard Convertible Securities Fund Retail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://vanguard/role/S000002837ExpenseExampleNoRedemptionRetail</Role>
      <ShortName>Expense Example, No Redemption  (Vanguard Convertible Securities Fund Retail)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>2711903 - Schedule - Shareholder Fees (Vanguard Convertible Securities Fund Retail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://vanguard/role/S000002837ShareholderFeesRetail</Role>
      <ShortName>Shareholder Fees (Vanguard Convertible Securities Fund Retail)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>2711904 - Schedule - Annual Fund Operating Expenses  (Vanguard Convertible Securities Fund Retail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://vanguard/role/S000002837OperatingExpensesRetail</Role>
      <ShortName>Annual Fund Operating Expenses  (Vanguard Convertible Securities Fund Retail)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>2711914 - Schedule - Shareholder Fees (Vanguard Convertible Securities Fund Participant)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://vanguard/role/S000002837ShareholderFeesParticipant</Role>
      <ShortName>Shareholder Fees (Vanguard Convertible Securities Fund Participant)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>2711915 - Schedule - Annual Fund Operating Expenses  (Vanguard Convertible Securities Fund Participant)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://vanguard/role/S000002837OperatingExpensesParticipant</Role>
      <ShortName>Annual Fund Operating Expenses  (Vanguard Convertible Securities Fund Participant)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>2711936 - Schedule - Annual Total Returns (Vanguard Convertible Securities Fund - Investor Shares Participant)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://vanguard/role/S000002837_C000007767BarChartParticipant</Role>
      <ShortName>Annual Total Returns (Vanguard Convertible Securities Fund - Investor Shares Participant)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>2711936 - Schedule - Annual Total Returns (Vanguard Convertible Securities Fund - Investor Shares Retail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://vanguard/role/S000002837_C000007767BarChartRetail</Role>
      <ShortName>Annual Total Returns (Vanguard Convertible Securities Fund - Investor Shares Retail)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>2711936 - Schedule - Expense Example, No Redemption {Transposed} (Vanguard Convertible Securities Fund Participant)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://vanguard/role/S000002837ExpenseExampleNoRedemptionParticipant</Role>
      <ShortName>Expense Example, No Redemption  (Vanguard Convertible Securities Fund Participant)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9999.htm</HtmlFileName>
      <LongName>Uncategorized Items</LongName>
      <ReportType>Sheet</ReportType>
      <Role />
      <ShortName>Uncategorized Items</ShortName>
    </Report>
    <Report>
      <IsDefault>true</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <Logs>
    <Log type="Warning">Element rr:AnnualFundOperatingExpensesTableTextBlock in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:AnnualFundOperatingExpensesTableTextBlock in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:BarChartAndPerformanceTableHeading in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:BarChartAndPerformanceTableHeading in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:BarChartClosingTextBlock in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:BarChartClosingTextBlock in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:BarChartHeading in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:BarChartHeading in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:BarChartNarrativeTextBlock in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:BarChartNarrativeTextBlock in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:BarChartTableTextBlock in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:BarChartTableTextBlock in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:ExpenseExampleHeading in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:ExpenseExampleHeading in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:ExpenseExampleNarrativeTextBlock in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:ExpenseExampleNarrativeTextBlock in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:ExpenseExampleNoRedemptionTableTextBlock in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:ExpenseExampleNoRedemptionTableTextBlock in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:ExpenseHeading in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:ExpenseHeading in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:ExpenseNarrativeTextBlock in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:ExpenseNarrativeTextBlock in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:HighestQuarterlyReturnLabel in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:HighestQuarterlyReturnLabel in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:IndexNoDeductionForFeesExpensesTaxes in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:IndexNoDeductionForFeesExpensesTaxes in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:IndexNoDeductionForFeesExpensesTaxes in context v_Participant_S000002837_C000007767_BankofAmericaMerrillLynchAllUSConvertiblesMember was not presented.</Log>
    <Log type="Warning">Element rr:IndexNoDeductionForFeesExpensesTaxes in context v_Participant_S000002837_C000007767_ConvertiblesCompositeIndexMember was not presented.</Log>
    <Log type="Warning">Element rr:IndexNoDeductionForFeesExpensesTaxes in context v_Participant_S000002837_C000007767_ConvertibleSecuritiesFundsAverageMember was not presented.</Log>
    <Log type="Warning">Element rr:IndexNoDeductionForFeesExpensesTaxes in context v_Retail_S000002837_C000007767_BankofAmericaMerrillLynchAllUSConvertiblesMember was not presented.</Log>
    <Log type="Warning">Element rr:IndexNoDeductionForFeesExpensesTaxes in context v_Retail_S000002837_C000007767_ConvertiblesCompositeIndexMember was not presented.</Log>
    <Log type="Warning">Element rr:IndexNoDeductionForFeesExpensesTaxes in context v_Retail_S000002837_C000007767_ConvertibleSecuritiesFundsAverageMember was not presented.</Log>
    <Log type="Warning">Element rr:LowestQuarterlyReturnLabel in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:LowestQuarterlyReturnLabel in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:ObjectiveHeading in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:ObjectiveHeading in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:ObjectivePrimaryTextBlock in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:ObjectivePrimaryTextBlock in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:OperatingExpensesCaption in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:OperatingExpensesCaption in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PerformanceAdditionalMarketIndex in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PerformanceAdditionalMarketIndex in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PerformanceAvailabilityPhone in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PerformanceAvailabilityPhone in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PerformanceAvailabilityWebSiteAddress in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PerformanceAvailabilityWebSiteAddress in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PerformanceInformationIllustratesVariabilityOfReturns in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PerformanceInformationIllustratesVariabilityOfReturns in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PerformancePastDoesNotIndicateFuture in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PerformancePastDoesNotIndicateFuture in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PerformanceTableClosingTextBlock in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PerformanceTableExplanationAfterTaxHigher in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PerformanceTableHeading in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PerformanceTableHeading in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PerformanceTableNotRelevantToTaxDeferred in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PerformanceTableTextBlock in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PerformanceTableTextBlock in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PerformanceTableUsesHighestFederalRate in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PortfolioTurnoverHeading in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PortfolioTurnoverHeading in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PortfolioTurnoverRate in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PortfolioTurnoverRate in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PortfolioTurnoverTextBlock in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:PortfolioTurnoverTextBlock in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:ProspectusDate in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:ProspectusDate in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:RiskHeading in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:RiskHeading in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:RiskLoseMoney in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:RiskLoseMoney in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:RiskNarrativeTextBlock in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:RiskNarrativeTextBlock in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:RiskNotInsuredDepositoryInstitution in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:RiskNotInsuredDepositoryInstitution in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:RiskReturnHeading in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:RiskReturnHeading in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:ShareholderFeesCaption in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:ShareholderFeesCaption in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:ShareholderFeesTableTextBlock in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:ShareholderFeesTableTextBlock in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:StrategyHeading in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:StrategyHeading in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:StrategyNarrativeTextBlock in context v_Participant_S000002837 was not presented.</Log>
    <Log type="Warning">Element rr:StrategyNarrativeTextBlock in context v_Retail_S000002837 was not presented.</Log>
    <Log type="Warning">Element vanguard:ComparativeBenchmark in context v_S000002837_C000007767 was not presented.</Log>
  </Logs>
  <InputFiles>
    <File>convertible-20150325.xml</File>
    <File>convertible-20150325.xsd</File>
    <File>convertible-20150325_cal.xml</File>
    <File>convertible-20150325_def.xml</File>
    <File>convertible-20150325_lab.xml</File>
    <File>convertible-20150325_pre.xml</File>
  </InputFiles>
  <SupplementalFiles />
  <BaseTaxonomies />
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
