Fiduciary Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Fiduciary Assets and Liabilities [Line Items]
Net uncollected premiums and claims receivable and payable	$ 12,500		$ 12,500		$ 13,000
Risk and Insurance Services
Fiduciary Assets and Liabilities [Line Items]
Interest on fiduciary funds	40	$ 4	57	$ 12
Operating Segments | Risk and Insurance Services
Fiduciary Assets and Liabilities [Line Items]
Interest on fiduciary funds	$ 40	$ 4	$ 57	$ 12