Restructuring Costs (Restructuring and Related Costs Incurred) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025	Dec. 31, 2025
Restructuring Cost and Reserve [Line Items]
Total	$ 79	$ 46	$ 182	$ 96	$ 222
Corporate
Restructuring Cost and Reserve [Line Items]
Total	25	8	41	13
Risk and Insurance Services \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Total	44	20	110	51
Consulting \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Total	$ 10	$ 18	$ 31	$ 32

- 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.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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