Claim, Claim Adjustment Expense and Future Policy Benefit Reserves, Gross and Net Carried Reserves (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Gross and Net Carried Reserves [Abstract]
Gross case reserves	$ 10,555	$ 10,694
Gross IBNR reserves	13,619	12,012
Total gross carried claim and claim adjustment expense reserves	24,174	22,706
Net case reserves	8,369	8,930
Net IBNR reserves	10,836	9,771
Total net carried claim and claim adjustment expense reserves	19,205	18,701	$ 17,885	$ 17,965
Property and casualty
Gross and Net Carried Reserves [Abstract]
Gross case reserves	5,621	5,674
Gross IBNR reserves	11,982	10,415
Total gross carried claim and claim adjustment expense reserves	17,603	16,089
Net case reserves	4,932	5,072
Net IBNR reserves	10,338	9,123
Total net carried claim and claim adjustment expense reserves	15,270	14,195
Insurance, Other
Gross and Net Carried Reserves [Abstract]
Gross case reserves	4,934	5,020
Gross IBNR reserves	1,637	1,597
Total gross carried claim and claim adjustment expense reserves	6,571	6,617
Net case reserves	3,437	3,858
Net IBNR reserves	498	648
Total net carried claim and claim adjustment expense reserves	$ 3,935	$ 4,506