Claim and Claim Adjustment Expense Reserves and Future Policy Benefit Reserves (Reconciliation of Liability for Unpaid Claim and Claim Adjustment Expense) (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Liability for Claims and Claims Adjustment Expense [Line Items]
Total Net Carried Claim and Claim Adjustment Expense Reserves	$ 19,908	$ 19,205	$ 18,701	$ 17,885
Reinsurance receivables	5,191
Total gross liability for unpaid claim and claim adjustment expenses	25,099	24,174
Specialty
Liability for Claims and Claims Adjustment Expense [Line Items]
Total Net Carried Claim and Claim Adjustment Expense Reserves	5,563	5,265
Reinsurance receivables	1,315
Commercial
Liability for Claims and Claims Adjustment Expense [Line Items]
Total Net Carried Claim and Claim Adjustment Expense Reserves	8,430	8,065
Reinsurance receivables	965
International
Liability for Claims and Claims Adjustment Expense [Line Items]
Total Net Carried Claim and Claim Adjustment Expense Reserves	2,003	1,940
Reinsurance receivables	400
Life and Group
Liability for Claims and Claims Adjustment Expense [Line Items]
Total Net Carried Claim and Claim Adjustment Expense Reserves	3,573
Reinsurance receivables	101
Corporate & Other
Liability for Claims and Claims Adjustment Expense [Line Items]
Total Net Carried Claim and Claim Adjustment Expense Reserves	339	$ 294
Reinsurance receivables	$ 2,410