Claim, Claim Adjustment Expense and Future Policy Benefit Reserves (Gross and Net Carried Claim and Claim Adjustment Expense Reserves) (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]
Gross Case Reserves	$ 10,555	$ 10,694
Gross IBNR Reserves	13,619	12,012
Total Gross Carried Claim and Claim Adjustment Expense Reserves	24,174	22,706	$ 21,720	$ 21,984
Net Case Reserves	8,369	8,930
Net IBNR Reserves	10,836	9,771
Total Net Carried Claim and Claim Adjustment Expense Reserves	19,205	18,701	$ 17,885	$ 17,965
Specialty
Liability for Claims and Claims Adjustment Expense [Line Items]
Gross Case Reserves	1,578	1,567
Gross IBNR Reserves	4,855	4,181
Total Gross Carried Claim and Claim Adjustment Expense Reserves	6,433	5,748
Net Case Reserves	1,338	1,410
Net IBNR Reserves	3,927	3,488
Total Net Carried Claim and Claim Adjustment Expense Reserves	5,265	4,898
Commercial
Liability for Claims and Claims Adjustment Expense [Line Items]
Gross Case Reserves	3,184	3,215
Gross IBNR Reserves	5,706	5,035
Total Gross Carried Claim and Claim Adjustment Expense Reserves	8,890	8,250
Net Case Reserves	2,850	2,885
Net IBNR Reserves	5,215	4,590
Total Net Carried Claim and Claim Adjustment Expense Reserves	8,065	7,475
International
Liability for Claims and Claims Adjustment Expense [Line Items]
Gross Case Reserves	859	892
Gross IBNR Reserves	1,421	1,199
Total Gross Carried Claim and Claim Adjustment Expense Reserves	2,280	2,091
Net Case Reserves	744	777
Net IBNR Reserves	1,196	1,045
Total Net Carried Claim and Claim Adjustment Expense Reserves	1,940	1,822
Life & Group
Liability for Claims and Claims Adjustment Expense [Line Items]
Gross Case Reserves	3,383	3,406
Gross IBNR Reserves	371	337
Total Gross Carried Claim and Claim Adjustment Expense Reserves	3,754	3,743
Net Case Reserves	3,291	3,298
Net IBNR Reserves	350	317
Total Net Carried Claim and Claim Adjustment Expense Reserves	3,641	3,615
Corporate & Other
Liability for Claims and Claims Adjustment Expense [Line Items]
Gross Case Reserves	1,551	1,614
Gross IBNR Reserves	1,266	1,260
Total Gross Carried Claim and Claim Adjustment Expense Reserves	2,817	2,874
Net Case Reserves	146	560
Net IBNR Reserves	148	331
Total Net Carried Claim and Claim Adjustment Expense Reserves	$ 294	$ 891