Goodwill and Other Intangibles (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Indefinite-lived intangible assets	$ 0		$ 0
Goodwill	17,314,000,000	$ 16,300,000,000	$ 17,231,000,000	$ 16,251,000,000
Aggregate amortization expense	90,000,000	$ 85,000,000
Risk and Insurance Services
Segment Reporting Information [Line Items]
Goodwill expected to be tax deductible	38,000,000
Goodwill	13,200,000,000
Consulting
Segment Reporting Information [Line Items]
Goodwill expected to be tax deductible	81,000,000
Goodwill	$ 4,100,000,000