Claim and Claim Adjustment Expense Reserves and Future Policy Benefit Reserves - Gross and Net Carried Reserves (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Gross and Net Carried Reserves [Abstract]
Gross Case Reserves	$ 10,387	$ 10,555
Gross IBNR Reserves	14,712	13,619
Total Gross Carried Claim and Claim Adjustment Expense Reserves	25,099	24,174
Net Case Reserves	8,319	8,369
Net IBNR Reserves	11,589	10,836
Total net carried claim and claim adjustment expense reserves	19,908	19,205	$ 18,701	$ 17,885
Property and casualty
Gross and Net Carried Reserves [Abstract]
Gross Case Reserves	5,502	5,621
Gross IBNR Reserves	13,174	11,982
Total Gross Carried Claim and Claim Adjustment Expense Reserves	18,676	17,603
Net Case Reserves	4,805	4,932
Net IBNR Reserves	11,191	10,338
Total net carried claim and claim adjustment expense reserves	15,996	15,270
Other insurance
Gross and Net Carried Reserves [Abstract]
Gross Case Reserves	4,885	4,934
Gross IBNR Reserves	1,538	1,637
Total Gross Carried Claim and Claim Adjustment Expense Reserves	6,423	6,571
Net Case Reserves	3,514	3,437
Net IBNR Reserves	398	498
Total net carried claim and claim adjustment expense reserves	$ 3,912	$ 3,935