Goodwill and Other Intangibles (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Indefinite lived identified intangible assets	$ 0	$ 0
Goodwill	17,231,000,000	16,251,000,000	$ 16,317,000,000
Aggregate amortization expense	343,000,000	338,000,000	$ 365,000,000
Risk and Insurance Services
Segment Reporting Information [Line Items]
Goodwill expected to be tax deductible	230,000,000	348,000,000
Goodwill	13,200,000,000
Consulting Segment
Segment Reporting Information [Line Items]
Goodwill expected to be tax deductible	12,000,000	$ 64,000,000
Goodwill	$ 4,000,000,000