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Restructuring Costs (Narrative) (Details) - USD ($) $ in Millions |  | 3 Months Ended |
--- | --- | --- | ---
Mar. 31, 2023 | Mar. 31, 2023 | Mar. 31, 2022 | Dec. 31, 2022
Restructuring Cost and Reserve [Line Items] |  |  |  |
Costs incurred |  | $ 53 | $ 30 |
Severance and Lease Exit Charges |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |
Costs incurred | $ 243 | 24 |  |
Minimum |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |
Estimated remaining costs |  |  |  | $ 375
Maximum |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |
Estimated remaining costs |  |  |  | $ 400
Corporate |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |
Costs incurred |  | 12 | 8 |
Risk and Insurance Services |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |
Costs incurred |  | 32 | 16 |
Consulting |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |
Costs incurred |  | $ 9 | $ 6 |

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