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Segment Information (Selected Information and Details Of Operating Segment Revenue) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Segment Reporting Information [Line Items] |  |  |
Revenue | $ 19,820 | $ 17,224 | $ 16,652
Fixed Assets, Net | 847 | 856 | 858
Risk and Insurance Services |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | 12,085 | 10,337 | 9,599
Consulting |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | 7,789 | 6,976 | 7,143
United States |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | 9,343 | 8,168 | 7,840
Fixed Assets, Net | 484 | 492 | 462
United Kingdom |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | 3,130 | 2,818 | 2,679
Fixed Assets, Net | 116 | 115 | 149
Continental Europe |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | 3,219 | 2,881 | 2,837
Fixed Assets, Net | 68 | 74 | 68
Asia Pacific |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | 2,617 | 2,093 | 2,001
Fixed Assets, Net | 96 | 105 | 101
Asia Pacific | Risk and Insurance Services |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | 1,462 | 1,059 | 953
Other |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | 1,565 | 1,353 | 1,385
Fixed Assets, Net | 83 | 70 | 78
Operating Segments |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | 19,874 | 17,313 | 16,742
Operating Segments | Risk and Insurance Services |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | 12,085 | 10,337 | 9,599
Gain (loss) on consolidation of business | 267 |  |
Operating Segments | Consulting |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | 7,789 | 6,976 | 7,143
Corporate/Eliminations |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | (54) | (89) | (90)
Marsh | Risk and Insurance Services |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | 10,203 | 8,595 | 8,014
Marsh | Operating Segments | Risk and Insurance Services |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | 10,214 | 8,628 | 8,085
Guy Carpenter | Risk and Insurance Services |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | 1,867 | 1,696 | 1,480
Guy Carpenter | Operating Segments | Risk and Insurance Services |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | 1,871 | 1,709 | 1,514
Mercer | Consulting |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | 5,254 | 4,928 | 5,021
Mercer | Operating Segments | Consulting |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | 5,254 | 4,928 | 5,021
Oliver Wyman Group | Consulting |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | 2,535 | 2,048 | 2,122
Oliver Wyman Group | Operating Segments | Consulting |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | $ 2,535 | $ 2,048 | $ 2,122

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- Definition Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(14)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(8)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 360 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=124429447&loc=SL124453093-239630 Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(13)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 6: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 852 -SubTopic 10 -Section 55 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=84165509&loc=d3e56426-112766 + Details
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