Restructuring Costs (Restructuring and Related Costs Incurred) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025	Dec. 31, 2025
Restructuring Cost and Reserve [Line Items]
Total	$ 58	$ 18	$ 103	$ 50	$ 222
Corporate
Restructuring Cost and Reserve [Line Items]
Total	11	4	16	5
Risk and Insurance Services \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Total	39	8	66	31
Consulting \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Total	$ 8	$ 6	$ 21	$ 14

- 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.

+ References + Details

- 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.

+ References + Details