Goodwill and Other Intangibles (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Indefinite-lived intangible assets	$ 0		$ 0		$ 0
Goodwill	16,655,000,000	$ 15,576,000,000	16,655,000,000	$ 15,576,000,000	$ 16,251,000,000	$ 16,317,000,000
Aggregate amortization expense	85,000,000	$ 84,000,000	257,000,000	$ 258,000,000
Risk and Insurance Services
Segment Reporting Information [Line Items]
Goodwill expected to be tax deductible	234,000,000		234,000,000
Goodwill	12,700,000,000		12,700,000,000
Consulting
Segment Reporting Information [Line Items]
Goodwill expected to be tax deductible	12,000,000		12,000,000
Goodwill	$ 4,000,000,000		$ 4,000,000,000