Restructuring Costs (Restructuring and Related Costs) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Restructuring Cost and Reserve [Line Items]
Total	$ 18	$ 44	$ 50	$ 86	$ 276
Corporate
Restructuring Cost and Reserve [Line Items]
Total	4	10	5	19
Risk and Insurance Services \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Total	8	29	31	51
Consulting \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Total	$ 6	$ 5	$ 14	$ 16

- 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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