Claim and Claim Adjustment Expense Reserves (Gross and Net Carried Claim and Claim Adjustment Expense Reserves) (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Liability for Claims and Claims Adjustment Expense [Line Items]
Gross Case Reserves	$ 9,063	$ 8,402
Gross IBNR Reserves	17,536	16,574
Total Gross Carried Claim and Claim Adjustment Expense Reserves	26,599	24,976	$ 23,304	$ 22,120
Net Case Reserves	6,814	6,207
Net IBNR Reserves	13,803	13,056
Total Net Carried Claim and Claim Adjustment Expense Reserves	20,617	19,263	$ 18,163	$ 16,929
Specialty
Liability for Claims and Claims Adjustment Expense [Line Items]
Gross Case Reserves	2,166	2,023
Gross IBNR Reserves	5,618	5,403
Total Gross Carried Claim and Claim Adjustment Expense Reserves	7,784	7,426
Net Case Reserves	1,801	1,697
Net IBNR Reserves	4,387	4,282
Total Net Carried Claim and Claim Adjustment Expense Reserves	6,188	5,979
Commercial
Liability for Claims and Claims Adjustment Expense [Line Items]
Gross Case Reserves	4,093	3,690
Gross IBNR Reserves	8,156	7,646
Total Gross Carried Claim and Claim Adjustment Expense Reserves	12,249	11,336
Net Case Reserves	3,508	3,135
Net IBNR Reserves	7,188	6,804
Total Net Carried Claim and Claim Adjustment Expense Reserves	10,696	9,939
International
Liability for Claims and Claims Adjustment Expense [Line Items]
Gross Case Reserves	1,052	876
Gross IBNR Reserves	2,324	2,044
Total Gross Carried Claim and Claim Adjustment Expense Reserves	3,376	2,920
Net Case Reserves	880	741
Net IBNR Reserves	1,961	1,675
Total Net Carried Claim and Claim Adjustment Expense Reserves	2,841	2,416
Life & Group
Liability for Claims and Claims Adjustment Expense [Line Items]
Gross Case Reserves	556	572
Gross IBNR Reserves	35	50
Total Gross Carried Claim and Claim Adjustment Expense Reserves	591	622
Net Case Reserves	506	514
Net IBNR Reserves	29	27
Total Net Carried Claim and Claim Adjustment Expense Reserves	535	541
Corporate & Other
Liability for Claims and Claims Adjustment Expense [Line Items]
Gross Case Reserves	1,196	1,241
Gross IBNR Reserves	1,403	1,431
Total Gross Carried Claim and Claim Adjustment Expense Reserves	2,599	2,672
Net Case Reserves	119	120
Net IBNR Reserves	238	268
Total Net Carried Claim and Claim Adjustment Expense Reserves	$ 357	$ 388