XML 75 R64.htm IDEA: XBRL DOCUMENT
v3.21.2

Leases (Narrative) (Details) $ in Millions | 9 Months Ended
--- | ---
Sep. 30, 2021 USD ($)
Lessee, Lease, Description [Line Items] |
Lessee, operating lease, lease not yet commenced, amount | $ 13
Minimum |
Lessee, Lease, Description [Line Items] |
Lessee, operating lease, term of contract (years) | 10 years
Maximum |
Lessee, Lease, Description [Line Items] |
Lessee, operating lease, term of contract (years) | 25 years
Office Space |
Lessee, Lease, Description [Line Items] |
Lease obligations, percent | 99.00%

X
- Definition Lease Obligations, Percent + References No definition available. + Details
Name: | mmc_LeaseObligationsPercent
Namespace Prefix: | mmc_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Lessee, Operating Lease, Lease Not yet Commenced, Amount + References No definition available. + Details
Name: | mmc_LesseeOperatingLeaseLeaseNotYetCommencedAmount
Namespace Prefix: | mmc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- 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 No definition available. + Details
Name: | us-gaap_LesseeLeaseDescriptionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=123408670&loc=SL77918673-209980 + Details
Name: | us-gaap_LesseeOperatingLeaseTermOfContract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=srt_OfficeBuildingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |