<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.25.4</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>42</ContextCount>
  <ElementCount>32</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>11</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>1</UnitCount>
  <MyReports>
    <Report instance="mco-20260304.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>995100 - Document - Cover</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/dei/role/document/Cover</Role>
      <ShortName>Cover</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="mco-20260304.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>995410 - Disclosure - Pay vs Performance Disclosure</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/PvpDisclosure</Role>
      <ShortName>Pay vs Performance Disclosure</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="mco-20260304.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>995443 - Disclosure - Award Timing Disclosure</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/AwardTimingDisclosure</Role>
      <ShortName>Award Timing Disclosure</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="mco-20260304.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>995447 - Disclosure - Insider Trading Policies and Procedures</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/InsiderTradingPoliciesProc</Role>
      <ShortName>Insider Trading Policies and Procedures</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File doctype="DEF 14A" isProxy="true" isUsgaap="true" original="mco-20260304.htm">mco-20260304.htm</File>
    <File>mco-20260304.xsd</File>
    <File>mco-20260304_def.xml</File>
    <File>mco-20260304_lab.xml</File>
    <File>mco-20260304_pre.xml</File>
  </InputFiles>
  <SupplementalFiles>
    <File>mco-20260304_g1.jpg</File>
    <File>mco-20260304_g10.gif</File>
    <File>mco-20260304_g11.gif</File>
    <File>mco-20260304_g12.jpg</File>
    <File>mco-20260304_g13.jpg</File>
    <File>mco-20260304_g14.jpg</File>
    <File>mco-20260304_g15.jpg</File>
    <File>mco-20260304_g16.jpg</File>
    <File>mco-20260304_g17.jpg</File>
    <File>mco-20260304_g18.jpg</File>
    <File>mco-20260304_g19.jpg</File>
    <File>mco-20260304_g2.jpg</File>
    <File>mco-20260304_g20.jpg</File>
    <File>mco-20260304_g21.jpg</File>
    <File>mco-20260304_g22.jpg</File>
    <File>mco-20260304_g23.jpg</File>
    <File>mco-20260304_g24.jpg</File>
    <File>mco-20260304_g25.jpg</File>
    <File>mco-20260304_g26.jpg</File>
    <File>mco-20260304_g27.jpg</File>
    <File>mco-20260304_g28.jpg</File>
    <File>mco-20260304_g29.gif</File>
    <File>mco-20260304_g3.jpg</File>
    <File>mco-20260304_g30.gif</File>
    <File>mco-20260304_g31.gif</File>
    <File>mco-20260304_g32.jpg</File>
    <File>mco-20260304_g33.jpg</File>
    <File>mco-20260304_g34.jpg</File>
    <File>mco-20260304_g35.jpg</File>
    <File>mco-20260304_g36.jpg</File>
    <File>mco-20260304_g37.jpg</File>
    <File>mco-20260304_g38.jpg</File>
    <File>mco-20260304_g39.jpg</File>
    <File>mco-20260304_g4.jpg</File>
    <File>mco-20260304_g40.jpg</File>
    <File>mco-20260304_g5.gif</File>
    <File>mco-20260304_g6.gif</File>
    <File>mco-20260304_g7.gif</File>
    <File>mco-20260304_g8.gif</File>
    <File>mco-20260304_g9.gif</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy items="5">http://fasb.org/us-gaap/2025</BaseTaxonomy>
    <BaseTaxonomy items="4">http://xbrl.sec.gov/dei/2025</BaseTaxonomy>
    <BaseTaxonomy items="93">http://xbrl.sec.gov/ecd/2025</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>false</HasCalculationLinkbase>
</FilingSummary>
