3.26.1 html 158 105 1 false 32 0 false 7 false false R1.htm 0000001 - Document - Cover Sheet http://www.mmc.com/role/Cover Cover Cover 1 false false R2.htm 0000002 - Statement - STATEMENTS OF NET ASSETS AVAILABLE FOR BENEFITS Sheet http://www.mmc.com/role/STATEMENTSOFNETASSETSAVAILABLEFORBENEFITS STATEMENTS OF NET ASSETS AVAILABLE FOR BENEFITS Statements 2 false false R3.htm 0000003 - Statement - STATEMENT OF CHANGES IN NET ASSETS AVAILABLE FOR BENEFITS Sheet http://www.mmc.com/role/STATEMENTOFCHANGESINNETASSETSAVAILABLEFORBENEFITS STATEMENT OF CHANGES IN NET ASSETS AVAILABLE FOR BENEFITS Statements 3 false false R4.htm 0000004 - Disclosure - Description of the Plan Sheet http://www.mmc.com/role/DescriptionofthePlan Description of the Plan Notes 4 false false R5.htm 0000005 - Disclosure - Summary of Significant Accounting Policies Sheet http://www.mmc.com/role/SummaryofSignificantAccountingPolicies Summary of Significant Accounting Policies Notes 5 false false R6.htm 0000006 - Disclosure - Interest in Master Trust Sheet http://www.mmc.com/role/InterestinMasterTrust Interest in Master Trust Notes 6 false false R7.htm 0000007 - Disclosure - Fair Value Measurements Sheet http://www.mmc.com/role/FairValueMeasurements Fair Value Measurements Notes 7 false false R8.htm 0000008 - Disclosure - Net Asset Value (NAV) Per Share Sheet http://www.mmc.com/role/NetAssetValueNAVPerShare Net Asset Value (NAV) Per Share Notes 8 false false R9.htm 0000009 - Disclosure - Exempt Party in Interest Transactions Sheet http://www.mmc.com/role/ExemptPartyinInterestTransactions Exempt Party in Interest Transactions Notes 9 false false R10.htm 0000010 - Disclosure - Net Transfers to Other Plan Sheet http://www.mmc.com/role/NetTransferstoOtherPlan Net Transfers to Other Plan Notes 10 false false R11.htm 0000011 - Disclosure - Federal Income Tax Status Sheet http://www.mmc.com/role/FederalIncomeTaxStatus Federal Income Tax Status Notes 11 false false R12.htm 0000012 - Disclosure - Plan Termination Sheet http://www.mmc.com/role/PlanTermination Plan Termination Notes 12 false false R13.htm 0000013 - Disclosure - Reconciliation of Financial Statements to Form 5500 Sheet http://www.mmc.com/role/ReconciliationofFinancialStatementstoForm5500 Reconciliation of Financial Statements to Form 5500 Notes 13 false false R14.htm 0000014 - Disclosure - Subsequent Events Sheet http://www.mmc.com/role/SubsequentEvents Subsequent Events Notes 14 false false R15.htm 0000015 - Disclosure - SCHEDULE H, PART IV, LINE 4i SCHEDULE OF ASSETS (HELD AT END OF YEAR) Sheet http://www.mmc.com/role/SCHEDULEHPARTIVLINE4iSCHEDULEOFASSETSHELDATENDOFYEAR SCHEDULE H, PART IV, LINE 4i SCHEDULE OF ASSETS (HELD AT END OF YEAR) Notes 15 false false R16.htm 0000016 - Disclosure - Summary of Significant Accounting Policies (Policies) Sheet http://www.mmc.com/role/SummaryofSignificantAccountingPoliciesPolicies Summary of Significant Accounting Policies (Policies) Policies http://www.mmc.com/role/SummaryofSignificantAccountingPolicies 16 false false R17.htm 0000017 - Disclosure - Interest in Master Trust (Tables) Sheet http://www.mmc.com/role/InterestinMasterTrustTables Interest in Master Trust (Tables) Tables http://www.mmc.com/role/InterestinMasterTrust 17 false false R18.htm 0000018 - Disclosure - Fair Value Measurements (Tables) Sheet http://www.mmc.com/role/FairValueMeasurementsTables Fair Value Measurements (Tables) Tables http://www.mmc.com/role/FairValueMeasurements 18 false false R19.htm 0000019 - Disclosure - Net Asset Value (NAV) Per Share (Tables) Sheet http://www.mmc.com/role/NetAssetValueNAVPerShareTables Net Asset Value (NAV) Per Share (Tables) Tables http://www.mmc.com/role/NetAssetValueNAVPerShare 19 false false R20.htm 0000020 - Disclosure - Reconciliation of Financial Statements to Form 5500 (Tables) Sheet http://www.mmc.com/role/ReconciliationofFinancialStatementstoForm5500Tables Reconciliation of Financial Statements to Form 5500 (Tables) Tables http://www.mmc.com/role/ReconciliationofFinancialStatementstoForm5500 20 false false R21.htm 0000021 - Disclosure - Description of the Plan (Details) Sheet http://www.mmc.com/role/DescriptionofthePlanDetails Description of the Plan (Details) Details http://www.mmc.com/role/DescriptionofthePlan 21 false false R22.htm 0000022 - Disclosure - Summary of Significant Accounting Policies (Details) Sheet http://www.mmc.com/role/SummaryofSignificantAccountingPoliciesDetails Summary of Significant Accounting Policies (Details) Details http://www.mmc.com/role/SummaryofSignificantAccountingPoliciesPolicies 22 false false R23.htm 0000023 - Disclosure - Interest in Master Trust - Schedule of Master Trust Net Assets (Details) Sheet http://www.mmc.com/role/InterestinMasterTrustScheduleofMasterTrustNetAssetsDetails Interest in Master Trust - Schedule of Master Trust Net Assets (Details) Details 23 false false R24.htm 0000024 - Disclosure - Interest in Master Trust - Schedule of Net Investment Gain (Details) Sheet http://www.mmc.com/role/InterestinMasterTrustScheduleofNetInvestmentGainDetails Interest in Master Trust - Schedule of Net Investment Gain (Details) Details 24 false false R25.htm 0000025 - Disclosure - Interest in Master Trust - Narrative (Details) Sheet http://www.mmc.com/role/InterestinMasterTrustNarrativeDetails Interest in Master Trust - Narrative (Details) Details 25 false false R26.htm 0000026 - Disclosure - Fair Value Measurements (Details) Sheet http://www.mmc.com/role/FairValueMeasurementsDetails Fair Value Measurements (Details) Details http://www.mmc.com/role/FairValueMeasurementsTables 26 false false R27.htm 0000027 - Disclosure - Net Asset Value (NAV) Per Share (Details) Sheet http://www.mmc.com/role/NetAssetValueNAVPerShareDetails Net Asset Value (NAV) Per Share (Details) Details http://www.mmc.com/role/NetAssetValueNAVPerShareTables 27 false false R28.htm 0000028 - Disclosure - Exempt Party in Interest Transactions (Details) Sheet http://www.mmc.com/role/ExemptPartyinInterestTransactionsDetails Exempt Party in Interest Transactions (Details) Details http://www.mmc.com/role/ExemptPartyinInterestTransactions 28 false false R29.htm 0000029 - Disclosure - Net Transfers to Other Plan (Details) Sheet http://www.mmc.com/role/NetTransferstoOtherPlanDetails Net Transfers to Other Plan (Details) Details http://www.mmc.com/role/NetTransferstoOtherPlan 29 false false R30.htm 0000030 - Disclosure - Reconciliation of Financial Statements to Form 5500 - Reconciliation of Net Assets Available for Benefit (Details) Sheet http://www.mmc.com/role/ReconciliationofFinancialStatementstoForm5500ReconciliationofNetAssetsAvailableforBenefitDetails Reconciliation of Financial Statements to Form 5500 - Reconciliation of Net Assets Available for Benefit (Details) Details 30 false false R31.htm 0000031 - Disclosure - Reconciliation of Financial Statements to Form 5500 - Reconciliation of Benefits Paid and Decrease in Net Assets (Details) Sheet http://www.mmc.com/role/ReconciliationofFinancialStatementstoForm5500ReconciliationofBenefitsPaidandDecreaseinNetAssetsDetails Reconciliation of Financial Statements to Form 5500 - Reconciliation of Benefits Paid and Decrease in Net Assets (Details) Details 31 false false R32.htm 0000032 - Disclosure - SCHEDULE H, PART IV, LINE 4i SCHEDULE OF ASSETS (HELD AT END OF YEAR) (Details) Sheet http://www.mmc.com/role/SCHEDULEHPARTIVLINE4iSCHEDULEOFASSETSHELDATENDOFYEARDetails SCHEDULE H, PART IV, LINE 4i SCHEDULE OF ASSETS (HELD AT END OF YEAR) (Details) Details http://www.mmc.com/role/SCHEDULEHPARTIVLINE4iSCHEDULEOFASSETSHELDATENDOFYEAR 32 false false All Reports Book All Reports mrsh-20260622.htm mrsh-20260622.xsd mrsh-20260622_cal.xml mrsh-20260622_def.xml mrsh-20260622_lab.xml mrsh-20260622_pre.xml mrsh-20260622_g1.jpg http://fasb.org/us-gaap-ebp/2026 http://xbrl.sec.gov/dei/2026 true true