Restructuring Costs (Restructuring and Related Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 301	$ 427
Corporate, Non-Segment
Restructuring Cost and Reserve [Line Items]
Restructuring charges	62	96
Risk and Insurance Services
Restructuring Cost and Reserve [Line Items]
Restructuring charges	177	254
Consulting Segment
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 62	$ 77