v3.25.4

Segment Information (Geographic Area) (Details) - USD ($) $ in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Oct. 31, 2023 | Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023
Segment Reporting, Asset Reconciling Item [Line Items] |  |  |  |
Revenue |  | $ 26,981 | $ 24,458 | $ 22,736
Fixed Assets, Net |  | 829 | 859 | 882
Risk and Insurance Services | Guy Carpenter Reinsurance Group |  |  |  |
Segment Reporting, Asset Reconciling Item [Line Items] |  |  |  |
Gain from the settlement | $ 58 |  |  | 58
Operating Segments |  |  |  |
Segment Reporting, Asset Reconciling Item [Line Items] |  |  |  |
Revenue |  | 27,059 | 24,528 | 22,798
Operating Segments | Risk and Insurance Services |  |  |  |
Segment Reporting, Asset Reconciling Item [Line Items] |  |  |  |
Revenue |  | 17,265 | 15,395 | 14,089
Operating Segments | Risk and Insurance Services | Guy Carpenter Reinsurance Group |  |  |  |
Segment Reporting, Asset Reconciling Item [Line Items] |  |  |  |
Revenue |  | 2,635 | 2,544 | 2,432
Operating Segments | Consulting |  |  |  |
Segment Reporting, Asset Reconciling Item [Line Items] |  |  |  |
Revenue |  | 9,794 | 9,133 | 8,709
Operating Segments | Consulting | Marsh Management Consulting |  |  |  |
Segment Reporting, Asset Reconciling Item [Line Items] |  |  |  |
Revenue |  | 3,604 | 3,390 | 3,122
Pre-tax gain (loss) on sale |  |  | 20 |
Corporate/Eliminations |  |  |  |
Segment Reporting, Asset Reconciling Item [Line Items] |  |  |  |
Revenue |  | (78) | (70) | (62)
United States |  |  |  |
Segment Reporting, Asset Reconciling Item [Line Items] |  |  |  |
Revenue |  | 13,344 | 11,671 | 10,924
Fixed Assets, Net |  | 469 | 494 | 468
United States | Operating Segments | Technology Consulting And Administrative Solutions |  |  |  |
Segment Reporting, Asset Reconciling Item [Line Items] |  |  |  |
Pre-tax gain (loss) on sale |  | 15 |  |
United States | Operating Segments | Mercer U.S. Affinity Business | Consulting |  |  |  |
Segment Reporting, Asset Reconciling Item [Line Items] |  |  |  |
Pre-tax gain (loss) on sale |  |  | (35) |
United Kingdom |  |  |  |
Segment Reporting, Asset Reconciling Item [Line Items] |  |  |  |
Revenue |  | 3,816 | 3,595 | 3,555
Fixed Assets, Net |  | 136 | 150 | 168
United Kingdom | Operating Segments | Consulting | Mercer U K Pension Administration Businesses |  |  |  |
Segment Reporting, Asset Reconciling Item [Line Items] |  |  |  |
Pre-tax gain (loss) on sale |  |  | 70 |
Other |  |  |  |
Segment Reporting, Asset Reconciling Item [Line Items] |  |  |  |
Revenue |  | 9,899 | 9,262 | 8,319
Fixed Assets, Net |  | 224 | $ 215 | $ 246
Equity Method Investment, Realized Gain (Loss) on Disposal |  | $ 13 |  |

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