Restructuring Costs (Restructuring and Related Costs Incurred) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Restructuring Cost and Reserve [Line Items]
Total	$ 52	$ 38	$ 170	$ 96
Corporate
Restructuring Cost and Reserve [Line Items]
Total	9	15	48	36
Risk and Insurance Services
Restructuring Cost and Reserve [Line Items]
Total	26	18	89	44
Consulting
Restructuring Cost and Reserve [Line Items]
Total	$ 17	$ 5	$ 33	$ 16