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Goodwill and Other Intangibles (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2022 | Sep. 30, 2021 | Sep. 30, 2022 | Sep. 30, 2021 | Dec. 31, 2021 | Dec. 31, 2020
Segment Reporting Information [Line Items] |  |  |  |  |  |
Goodwill acquired |  |  | $ 139 | $ 374 |  |
Goodwill | $ 15,576 | $ 15,648 | 15,576 | 15,648 | $ 16,317 | $ 15,517
Aggregate amortization expense | 84 | $ 89 | 258 | $ 278 |  |
Risk and Insurance Services |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Goodwill acquired |  |  | 92 |  |  |
Goodwill, expected tax deductible amount | 92 |  | 92 |  |  |
Goodwill | 12,000 |  | 12,000 |  |  |
Consulting |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Goodwill acquired |  |  | 25 |  |  |
Goodwill, expected tax deductible amount | 25 |  | 25 |  |  |
Goodwill | $ 3,600 |  | $ 3,600 |  |  |

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