Claim and Claim Adjustment Expense Reserves - Net Liability for Unpaid Claim and Claim Adjustment Expenses (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Net Liability for Unpaid Claim and Claim Adjustment Expenses [Abstract]
Net claim and claim adjustment expenses	$ 19,263	$ 18,163	$ 16,929	$ 16,300
Total reinsurance receivables	5,713	5,141	5,191	4,969
Total gross liability for unpaid claims and claims adjustment expenses	24,976	23,304	$ 22,120	$ 21,269
Property and casualty
Net Liability for Unpaid Claim and Claim Adjustment Expenses [Abstract]
Net claim and claim adjustment expenses	18,334	17,213
Total reinsurance receivables	3,348
Other insurance
Net Liability for Unpaid Claim and Claim Adjustment Expenses [Abstract]
Net claim and claim adjustment expenses	929	$ 950
Total reinsurance receivables	$ 2,365