Insurance Claim Reserves (Details) - Claims and Claim Adjustment Expenses Reserves Summary - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	$ 57,447
Discount (Net of Reinsurance)	(1,028)
Subtotal: Net Claims and Claim Adjustment Expense Reserves	56,419
Reinsurance Recoverables on Unpaid Losses	7,674
Claims and Claim Adjustment Expense Reserves	64,093	$ 61,627
Discount on reinsurance recoverables for long-term disability and annuity claim payments included in discount (net of reinsurance)	42
Reinsurance recoverables	8,000	8,143	$ 8,063
Property-casualty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	57,447
Discount (Net of Reinsurance)	(1,028)
Subtotal: Net Claims and Claim Adjustment Expense Reserves	56,419	53,804	50,853	$ 48,688
Reinsurance Recoverables on Unpaid Losses	7,669	7,817	7,790	8,209
Claims and Claim Adjustment Expense Reserves	64,088	61,621	$ 58,643	$ 56,897
Accident and health [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	0
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	0
Reinsurance Recoverables on Unpaid Losses	5
Claims and Claim Adjustment Expense Reserves	5	$ 6
Business Insurance [Member] | General liability [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	11,100
Business Insurance [Member] | Commercial property [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	1,266
Business Insurance [Member] | Commercial multi-peril [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	5,758
Business Insurance [Member] | Automobile [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	4,791
Business Insurance [Member] | Workers' compensation [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	15,757
Bond & Specialty Insurance [Member] | General liability [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	2,681
Bond & Specialty Insurance [Member] | Fidelity and surety [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	714
Personal Insurance [Member] | Automobile [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	4,302
Personal Insurance [Member] | Homeowners (excluding Other) [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	2,275
Personal Insurance [Member] | International - Canada [Member] | Property-casualty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	795
Reportable segments [Member] | Property-casualty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	49,439
Discount (Net of Reinsurance)	(1,024)
Subtotal: Net Claims and Claim Adjustment Expense Reserves	48,415
Reinsurance Recoverables on Unpaid Losses	3,386
Claims and Claim Adjustment Expense Reserves	51,801
Reportable segments [Member] | Business Insurance [Member] | General liability [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	11,100
Discount (Net of Reinsurance)	(124)
Subtotal: Net Claims and Claim Adjustment Expense Reserves	10,976
Reinsurance Recoverables on Unpaid Losses	1,140
Claims and Claim Adjustment Expense Reserves	12,116
Reportable segments [Member] | Business Insurance [Member] | Commercial property [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	1,266
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	1,266
Reinsurance Recoverables on Unpaid Losses	358
Claims and Claim Adjustment Expense Reserves	1,624
Reportable segments [Member] | Business Insurance [Member] | Commercial multi-peril [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	5,758
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	5,758
Reinsurance Recoverables on Unpaid Losses	318
Claims and Claim Adjustment Expense Reserves	6,076
Reportable segments [Member] | Business Insurance [Member] | Automobile [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	4,791
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	4,791
Reinsurance Recoverables on Unpaid Losses	298
Claims and Claim Adjustment Expense Reserves	5,089
Reportable segments [Member] | Business Insurance [Member] | Workers' compensation [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	15,757
Discount (Net of Reinsurance)	(900)
Subtotal: Net Claims and Claim Adjustment Expense Reserves	14,857
Reinsurance Recoverables on Unpaid Losses	554
Claims and Claim Adjustment Expense Reserves	15,411
Reportable segments [Member] | Bond & Specialty Insurance [Member] | General liability [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	2,681
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	2,681
Reinsurance Recoverables on Unpaid Losses	339
Claims and Claim Adjustment Expense Reserves	3,020
Reportable segments [Member] | Bond & Specialty Insurance [Member] | Fidelity and surety [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	714
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	714
Reinsurance Recoverables on Unpaid Losses	8
Claims and Claim Adjustment Expense Reserves	722
Reportable segments [Member] | Personal Insurance [Member] | Automobile [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	4,302
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	4,302
Reinsurance Recoverables on Unpaid Losses	320
Claims and Claim Adjustment Expense Reserves	4,622
Reportable segments [Member] | Personal Insurance [Member] | Homeowners (excluding Other) [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	2,275
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	2,275
Reinsurance Recoverables on Unpaid Losses	37
Claims and Claim Adjustment Expense Reserves	2,312
Reportable segments [Member] | Personal Insurance [Member] | International - Canada [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	795
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	795
Reinsurance Recoverables on Unpaid Losses	14
Claims and Claim Adjustment Expense Reserves	809
Reconciling Items [Member] | Other insurance contracts [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	5,036
Discount (Net of Reinsurance)	(4)
Subtotal: Net Claims and Claim Adjustment Expense Reserves	5,032
Reinsurance Recoverables on Unpaid Losses	1,735
Claims and Claim Adjustment Expense Reserves	6,767
Reconciling Items [Member] | Unallocated loss adjustment expense reserves [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	2,880
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	2,880
Reinsurance Recoverables on Unpaid Losses	17
Claims and Claim Adjustment Expense Reserves	2,897
Reconciling Items [Member] | Structured settlements [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	0
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	0
Reinsurance Recoverables on Unpaid Losses	2,583
Claims and Claim Adjustment Expense Reserves	2,583
Reconciling Items [Member] | Other [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	92
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	92
Reinsurance Recoverables on Unpaid Losses	(52)
Claims and Claim Adjustment Expense Reserves	$ 40