Claim and Claim Adjustment Expense Reserves (Reconciliation of Liability for Unpaid Claim and Claim Adjustment Expense) (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Liability for Claims and Claims Adjustment Expense [Line Items]
Total Net Carried Claim and Claim Adjustment Expense Reserves	$ 19,263	$ 18,163	$ 16,929	$ 16,300
Reinsurance receivables	5,713
Total gross liability for unpaid claim and claim adjustment expenses	24,976	23,304	$ 22,120
Specialty
Liability for Claims and Claims Adjustment Expense [Line Items]
Total Net Carried Claim and Claim Adjustment Expense Reserves	5,979	5,916
Reinsurance receivables	1,447
Commercial
Liability for Claims and Claims Adjustment Expense [Line Items]
Total Net Carried Claim and Claim Adjustment Expense Reserves	9,939	9,021
Reinsurance receivables	1,397
International
Liability for Claims and Claims Adjustment Expense [Line Items]
Total Net Carried Claim and Claim Adjustment Expense Reserves	2,416	2,276
Reinsurance receivables	504
Life and Group
Liability for Claims and Claims Adjustment Expense [Line Items]
Total Net Carried Claim and Claim Adjustment Expense Reserves	541
Reinsurance receivables	81
Corporate & Other
Liability for Claims and Claims Adjustment Expense [Line Items]
Total Net Carried Claim and Claim Adjustment Expense Reserves	388	$ 368
Reinsurance receivables	$ 2,284