EBP, Administrative Cost, Participant Paid Monthly Recordkeeping Fee

No definition available.

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Namespace Prefix:	mrsh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

EBP, Administrative Cost, Participant Paid New Loan Request Fee

+ References

No definition available.

+ Details

Name:	mrsh_EBPAdministrativeCostParticipantPaidNewLoanRequestFee
Namespace Prefix:	mrsh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

EBP, Administrative Cost, Participant Paid Withdrawal And Distribution Transaction Fee

+ References

No definition available.

+ Details

Name:	mrsh_EBPAdministrativeCostParticipantPaidWithdrawalAndDistributionTransactionFee
Namespace Prefix:	mrsh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

EBP, Administrative Cost, Participant Paid Yearly Recordkeeping Fee

+ References

No definition available.

+ Details

Name:	mrsh_EBPAdministrativeCostParticipantPaidYearlyRecordkeepingFee
Namespace Prefix:	mrsh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

EBP, Employer Contribution, Participant Compensation After Four Years Service, Percentage

+ References

No definition available.

+ Details

Name:	mrsh_EBPEmployerContributionParticipantCompensationAfterFourYearsServicePercentage
Namespace Prefix:	mrsh_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

EBP, Employer Contribution, Participant Compensation Matched After Five Years Of Service, Percentage

+ References

No definition available.

+ Details

Name:	mrsh_EBPEmployerContributionParticipantCompensationMatchedAfterFiveYearsOfServicePercentage
Namespace Prefix:	mrsh_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

EBP, Employer Contribution, Participant Compensation Matched Four To Five Years Service, Percentage

+ References

No definition available.

+ Details

Name:	mrsh_EBPEmployerContributionParticipantCompensationMatchedFourToFiveYearsServicePercentage
Namespace Prefix:	mrsh_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

EBP, Employer Contribution, Participant Compensation Matched Less Than Three Years Service, Percentage

+ References

No definition available.

+ Details

Name:	mrsh_EBPEmployerContributionParticipantCompensationMatchedLessThanThreeYearsServicePercentage
Namespace Prefix:	mrsh_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

EBP, Employer Contribution, Participant Compensation Matched Less Than Two Years Service, Percentage

+ References

No definition available.

+ Details

Name:	mrsh_EBPEmployerContributionParticipantCompensationMatchedLessThanTwoYearsServicePercentage
Namespace Prefix:	mrsh_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

EBP, Employer Contribution, Participant Compensation Matched Three To Four Years Service, Percentage

+ References

No definition available.

+ Details

Name:	mrsh_EBPEmployerContributionParticipantCompensationMatchedThreeToFourYearsServicePercentage
Namespace Prefix:	mrsh_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

EBP, Employer Contribution, Participant Compensation Matched Two To Three Years Service, Percentage

+ References

No definition available.

+ Details

Name:	mrsh_EBPEmployerContributionParticipantCompensationMatchedTwoToThreeYearsServicePercentage
Namespace Prefix:	mrsh_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

EBP, Employer Contribution, Participant Requisite Service Period

+ References

No definition available.

+ Details

Name:	mrsh_EBPEmployerContributionParticipantRequisiteServicePeriod
Namespace Prefix:	mrsh_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

EBP, Minimum Plan Eligibility Age

+ References

No definition available.

+ Details

Name:	mrsh_EBPMinimumPlanEligibilityAge
Namespace Prefix:	mrsh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

EBP, Note Receivable From Participant, Account, Borrowing Term

+ References

No definition available.

+ Details

Name:	mrsh_EBPNoteReceivableFromParticipantAccountBorrowingTerm
Namespace Prefix:	mrsh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

EBP, Participant Contribution, After Tax, Maximum Annual Compensation to Total Compensation, Percentage

+ References

No definition available.

+ Details

Name:	mrsh_EBPParticipantContributionAfterTaxMaximumAnnualCompensationToTotalCompensationPercentage
Namespace Prefix:	mrsh_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

EBP, Participant Contributions, Minimum Vested Balance To Request Distribution Upon Termination Of Service

+ References

No definition available.

+ Details

Name:	mrsh_EBPParticipantContributionsMinimumVestedBalanceToRequestDistributionUponTerminationOfService
Namespace Prefix:	mrsh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

EBP, Participant Loan, Basis Spread On Variable Rate

+ References

No definition available.

+ Details

Name:	mrsh_EBPParticipantLoanBasisSpreadOnVariableRate
Namespace Prefix:	mrsh_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

EBP, Plan Retirement Age

+ References

No definition available.

+ Details

Name:	mrsh_EBPPlanRetirementAge
Namespace Prefix:	mrsh_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

EBP, Vesting Service Period

+ References

No definition available.

+ Details

Name:	mrsh_EBPVestingServicePeriod
Namespace Prefix:	mrsh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478416/962-205-50-1

+ Details

Name:	us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of employer matching contribution on eligible participant contribution to employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References

+ Details

Name:	us-gaap-ebp_EmployeeBenefitPlanEmployerContributionMatchingPercentage
Namespace Prefix:	us-gaap-ebp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of participant compensation eligible for employer matching contribution for participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References

+ Details

Name:	us-gaap-ebp_EmployeeBenefitPlanEmployerContributionParticipantCompensationMatchedPercentage
Namespace Prefix:	us-gaap-ebp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of plan asset, in forfeited nonvested account, no longer allocated to participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References

+ Details

Name:	us-gaap-ebp_EmployeeBenefitPlanForfeitedNonvestedAccount
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of decrease in forfeited nonvested account of employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) from employer contribution.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 962
-SubTopic 325
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478873/962-325-55-17

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (j)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478416/962-205-50-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6A-04(5)(c))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477804/962-205-S99-1

+ Details

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Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of maximum account balance that participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) can borrow.

+ References

+ Details

Name:	us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantAccountMaximumBorrowingAmount
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage of maximum account balance that participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) can borrow to total participant account balance.

+ References

+ Details

Name:	us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantAccountMaximumBorrowingToTotalAccountPercentage
Namespace Prefix:	us-gaap-ebp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of eligible compensation contributed for participant automatically enrolled in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References

+ Details

Name:	us-gaap-ebp_EmployeeBenefitPlanParticipantContributionAutomaticDeferralRate
Namespace Prefix:	us-gaap-ebp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of maximum pretax annual compensation that participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)), is permitted to contribute to total pretax annual compensation.

+ References

+ Details

Name:	us-gaap-ebp_EmployeeBenefitPlanParticipantContributionPretaxMaximumAnnualCompensationToTotalCompensationPercentage
Namespace Prefix:	us-gaap-ebp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Interest rate on participant loan in schedule of asset held for investment of employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Employee Retirement Income Security Act of 1974
-Number 2520
-Section 103
-Subsection 10
-Paragraph b
-Subparagraph (1)(i)(D)
-Publisher DOL-EBSA

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6A-05(a)(Schedule I))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477804/962-205-S99-1

+ Details

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Namespace Prefix:	us-gaap-ebp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	dei_LegalEntityAxis=mrsh_EBP003Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
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- Details

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Description of the Plan (Details) - EBP 003		12 Months Ended	42 Months Ended	54 Months Ended
Description of the Plan (Details) - EBP 003	Jan. 01, 2006 h	Dec. 31, 2025 USD ($) Year	Dec. 31, 2005	Jun. 30, 2002	Dec. 31, 2024 USD ($)
EBP, Description of Plan [Line Items]
Minimum eligibility age of the plan		18 years
Before tax participant contribution limit, as % of eligible compensation		75.00%
After tax participant contribution limit, as % of eligible compensation		15.00%
Participant paid monthly recordkeeping fee		$ 1.63
Participant paid yearly recordkeeping fee		19.50
Participant paid transaction fees for certain in-service withdrawals and distribution requests		25
Participant paid new loan request fee		$ 50
Vesting service period		1 year
Employer contribution, matching percentage		50.00%
Employer contribution, participation compensation matched percentage		6.00%
Automatic eligible base pay percentage		4.00%
Plan retirement age \| Year		65
Matching contribution if vested less than 3 years of service				0.00%
Matching contribution if vested 3 to 4 years of service	66.67%		40.00%	33.00%
Matching contribution if vested 4 to 5 years of service			67.00%	67.00%
Matching contribution if vested more than 5 years of service			100.00%	100.00%
Matching contribution if vested less than 2 years of service	0.00%		0.00%
Matching contribution if vested 2 to 3 years of service	33.33%		20.00%
Matching contribution if vested after 4 years of service	100.00%
Employment service period \| h	1
Employer contributions funded from forfeited non-vested accounts		$ 6,671,780
Forfeited non-vested account balance		3			$ 603,215
Minimum vested balance to request distribution upon termination of service		1,000
Plan participants maximum borrowing amount from account		$ 50,000
Plan participants maximum borrowing percent from account		50.00%
Basis spread on variable rate of participant loan		1.00%
Minimum
EBP, Description of Plan [Line Items]
Loan borrowing term		1 year
Participant loan interest rate		4.25%
Maximum
EBP, Description of Plan [Line Items]
Loan borrowing term		5 years
Participant loan interest rate		9.50%