Goodwill and Other Intangibles (Narrative) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Indefinite-lived intangible assets	$ 0		$ 0		$ 0
Goodwill	17,516,000,000	$ 16,621,000,000	17,516,000,000	$ 16,621,000,000	$ 17,231,000,000	$ 16,251,000,000
Aggregate amortization expense	89,000,000	$ 87,000,000	179,000,000	$ 172,000,000
Risk and Insurance Services
Segment Reporting Information [Line Items]
Goodwill expected to be tax deductible	254,000,000		254,000,000
Goodwill	13,400,000,000		13,400,000,000
Consulting
Segment Reporting Information [Line Items]
Goodwill expected to be tax deductible	81,000,000		81,000,000
Goodwill	$ 4,100,000,000		$ 4,100,000,000