Fiduciary Assets and Liabilities (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Fiduciary Assets and Liabilities [Line Items]
Net uncollected premiums and claims receivable and payable	$ 14,400		$ 14,400		$ 13,000
Total assets	48,000		48,000		44,114
Risk and Insurance Services
Fiduciary Assets and Liabilities [Line Items]
Total assets					33,022
Consulting
Fiduciary Assets and Liabilities [Line Items]
Total assets					$ 10,446
Operating Segments | Risk and Insurance Services
Fiduciary Assets and Liabilities [Line Items]
Interest on fiduciary funds	$ 131	$ 40	$ 330	$ 57