XML 110 R96.htm IDEA: XBRL DOCUMENT
v3.20.4

Integration and Restructuring Costs (Restructuring Activity) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
Restructuring Reserve [Roll Forward] |  |
Beginning of period | $ 102 | $ 112
Amounts Accrued | 89 | 112
Cash payments | (100) | (112)
Non-Cash/Other | (10) | (10)
End of period | 81 | 102
Severance |  |
Restructuring Reserve [Roll Forward] |  |
Beginning of period | 51 | 73
Amounts Accrued | 39 | 73
Cash payments | (54) | (91)
Non-Cash/Other |  | (4)
End of period | 36 | 51
Future rent under non-cancelable leases and other costs |  |
Restructuring Reserve [Roll Forward] |  |
Beginning of period | 51 | 39
Amounts Accrued | 50 | 39
Cash payments | (46) | (21)
Non-Cash/Other | (10) | (6)
End of period | 45 | 51
JLT Transaction |  |
Restructuring Reserve [Roll Forward] |  |
Beginning of period | 47 | 0
Amounts Accrued | 251 | 335
Cash payments | (226) | (265)
Non-cash charges | (47) | (23)
End of period | 25 | 47
JLT Transaction | Severance |  |
Restructuring Reserve [Roll Forward] |  |
Beginning of period | 42 | 0
Amounts Accrued | 43 | 154
Cash payments | (69) | (112)
Non-cash charges | 0 | 0
End of period | 16 | 42
JLT Transaction | Real Estate Related Costs |  |
Restructuring Reserve [Roll Forward] |  |
Beginning of period | 5 | 0
Amounts Accrued | 69 | 38
Cash payments | (25) | (14)
Non-cash charges | (42) | (19)
End of period | 7 | 5
JLT Transaction | Information Technology |  |
Restructuring Reserve [Roll Forward] |  |
Beginning of period | 0 | 0
Amounts Accrued | 62 | 45
Cash payments | (55) | (45)
Non-cash charges | (5) | 0
End of period | 2 | 0
JLT Transaction | Consulting and Other Outside Services |  |
Restructuring Reserve [Roll Forward] |  |
Beginning of period | 0 | 0
Amounts Accrued | 77 | 98
Cash payments | (77) | (94)
Non-cash charges | 0 | (4)
End of period | $ 0 | $ 0

X
- Definition Amount of cash payments made as the result of exit or disposal activities. Excludes payments associated with a discontinued operation or an asset retirement obligation. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b)(2) -URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 17 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3367-108585 + Details
Name: | us-gaap_PaymentsForRestructuring
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 5.P.3) -URI http://asc.fasb.org/extlink&oid=115931487&loc=d3e140864-122747 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB Topic 5.P.4(b)) -URI http://asc.fasb.org/extlink&oid=115931487&loc=d3e140904-122747 + Details
Name: | us-gaap_RestructuringCharges
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Carrying amount (including both current and noncurrent portions of the accrual) as of the balance sheet date pertaining to a specified type of cost associated with exit from or disposal of business activities or restructuring pursuant to a duly authorized plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b)(2) -URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB TOPIC 5.P.4(b)) -URI http://asc.fasb.org/extlink&oid=115931487&loc=d3e140904-122747 + Details
Name: | us-gaap_RestructuringReserve
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
Name: | us-gaap_RestructuringReserveRollForward
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of decrease in the reserve for full or partial settlement through consideration other than cash. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB TOPIC 5.P.4(b)(2)) -URI http://asc.fasb.org/extlink&oid=115931487&loc=d3e140904-122747 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869 + Details
Name: | us-gaap_RestructuringReserveSettledWithoutCash2
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of foreign currency translation gain (loss) which decreases (increases) the restructuring reserve. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b)(2) -URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB Topic 5.P.4(b)(2)) -URI http://asc.fasb.org/extlink&oid=115931487&loc=d3e140904-122747 + Details
Name: | us-gaap_RestructuringReserveTranslationAdjustment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_RestructuringCostAndReserveAxis=us-gaap_EmployeeSeveranceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RestructuringCostAndReserveAxis=us-gaap_OtherRestructuringMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=mmc_JardineLloydThompsonGroupplcMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RestructuringCostAndReserveAxis=mmc_RealEstateRelatedCostsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RestructuringCostAndReserveAxis=mmc_InformationTechnologyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RestructuringCostAndReserveAxis=mmc_LegalConsultingandOtherOutsideServicesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |