<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.19.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>7</ContextCount>
  <ElementCount>21</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>9</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>1</UnitCount>
  <MyReports>
    <Report instance="ck0000353560-20190531.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>000001 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://Dreyfus.com/20190531/role/DocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory></MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="ck0000353560-20190531.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>020000 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - General Money Market Fund, Inc.</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://Dreyfus.com/20190531/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusGeneralMoneyMarketFundInc</Role>
      <ShortName>Risk/Return Summary- Class A Prospectus - General Money Market Fund, Inc.</ShortName>
      <MenuCategory></MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="ck0000353560-20190531.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>020002 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - General Money Market Fund, Inc.</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://Dreyfus.com/20190531/role/DisclosureRiskReturnDetailDataElementsClassAProspectusGeneralMoneyMarketFundInc</Role>
      <ShortName>Risk/Return Detail Data- Class A Prospectus - General Money Market Fund, Inc.</ShortName>
      <MenuCategory></MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="ck0000353560-20190531.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>020003 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - General Government Securities Money Market Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://Dreyfus.com/20190531/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusGeneralGovernmentSecuritiesMoneyMarketFund</Role>
      <ShortName>Risk/Return Summary- Class A Prospectus - General Government Securities Money Market Fund</ShortName>
      <MenuCategory></MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="ck0000353560-20190531.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>020005 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - General Government Securities Money Market Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://Dreyfus.com/20190531/role/DisclosureRiskReturnDetailDataElementsClassAProspectusGeneralGovernmentSecuritiesMoneyMarketFund</Role>
      <ShortName>Risk/Return Detail Data- Class A Prospectus - General Government Securities Money Market Fund</ShortName>
      <MenuCategory></MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="ck0000353560-20190531.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>020006 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - General Treasury Securities Money Market Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://Dreyfus.com/20190531/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusGeneralTreasurySecuritiesMoneyMarketFund</Role>
      <ShortName>Risk/Return Summary- Class A Prospectus - General Treasury Securities Money Market Fund</ShortName>
      <MenuCategory></MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="ck0000353560-20190531.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>020008 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - General Treasury Securities Money Market Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://Dreyfus.com/20190531/role/DisclosureRiskReturnDetailDataElementsClassAProspectusGeneralTreasurySecuritiesMoneyMarketFund</Role>
      <ShortName>Risk/Return Detail Data- Class A Prospectus - General Treasury Securities Money Market Fund</ShortName>
      <MenuCategory></MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="ck0000353560-20190531.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>040000 - Disclosure - Risk/Return Detail Data {Elements}</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/rr/role/RiskReturnDetailData</Role>
      <ShortName>Risk/Return Detail Data</ShortName>
      <MenuCategory></MenuCategory>
      <Position>8</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>ck0000353560-20190531.xml</File>
    <File>ck0000353560-20190531.xsd</File>
    <File>ck0000353560-20190531_cal.xml</File>
    <File>ck0000353560-20190531_def.xml</File>
    <File>ck0000353560-20190531_lab.xml</File>
    <File>ck0000353560-20190531_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://xbrl.sec.gov/rr/2012-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2012-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
