Fiduciary Assets and Liabilities (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Fiduciary Assets and Liabilities [Line Items]
Net uncollected premiums and claims receivable and payable	$ 16,700		$ 16,700		$ 13,000
Total assets	46,566		46,566		44,114
Risk and Insurance Services
Fiduciary Assets and Liabilities [Line Items]
Interest on fiduciary funds	108	$ 13	199	$ 17
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	$ 108	$ 13	$ 199	$ 17