XML 57 R46.htm IDEA: XBRL DOCUMENT
v3.21.2

Fiduciary Assets and Liabilities (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Dec. 31, 2020
Fiduciary Assets and Liabilities [Line Items] |  |  |  |  |
Net uncollected premiums and claims receivable and payable | $ 12,700 |  | $ 12,700 |  | $ 11,200
Risk and Insurance Services Segment |  |  |  |  |
Fiduciary Assets and Liabilities [Line Items] |  |  |  |  |
Interest on fiduciary funds | 4 | $ 8 | 12 | $ 40 |
Operating Segments | Risk and Insurance Services Segment |  |  |  |  |
Fiduciary Assets and Liabilities [Line Items] |  |  |  |  |
Interest on fiduciary funds | $ 4 | $ 8 | $ 12 | $ 40 |

X
- Definition Fiduciary Assets and Liabilities [Line Items] + References No definition available. + Details
Name: | mmc_FiduciaryAssetsandLiabilitiesLineItems
Namespace Prefix: | mmc_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Interest income earned on both U.S. and foreign fiduciary funds held in trust. + References No definition available. + Details
Name: | mmc_InterestIncomeFiduciaryAssets
Namespace Prefix: | mmc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Net uncollected premiums and claims and the related payables are not assets and liabilities of MMC and are not included in the accompanying consolidated balance sheets. + References No definition available. + Details
Name: | mmc_UncollectedPremiumsandClaimsNetofRelatedPayables
Namespace Prefix: | mmc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=mmc_RiskandInsuranceServicesSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ConsolidationItemsAxis=us-gaap_OperatingSegmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |