Claim, Claim Adjustment Expense and Future Policy Benefit Reserves (Reconciliation of Liability for Unpaid Claim and Claim Adjustment Expense) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Liability for Claims and Claims Adjustment Expense [Line Items]
Total Net Carried Claim and Claim Adjustment Expense Reserves	$ 19,205	$ 18,701	$ 17,885	$ 17,965
Reinsurance receivables	4,969
Total gross liability for unpaid claim and claim adjustment expenses	24,174	22,706
Specialty
Liability for Claims and Claims Adjustment Expense [Line Items]
Total Net Carried Claim and Claim Adjustment Expense Reserves	5,265	4,898
Reinsurance receivables	1,168
Commercial
Liability for Claims and Claims Adjustment Expense [Line Items]
Total Net Carried Claim and Claim Adjustment Expense Reserves	8,065	7,475
Reinsurance receivables	825
International
Liability for Claims and Claims Adjustment Expense [Line Items]
Total Net Carried Claim and Claim Adjustment Expense Reserves	1,940	1,822
Reinsurance receivables	340
Life and Group
Liability for Claims and Claims Adjustment Expense [Line Items]
Total Net Carried Claim and Claim Adjustment Expense Reserves	3,641
Reinsurance receivables	113
Corporate & Other
Liability for Claims and Claims Adjustment Expense [Line Items]
Total Net Carried Claim and Claim Adjustment Expense Reserves	294	$ 891
Reinsurance receivables	$ 2,523