Insurance Claim Reserves (Details) - Claims and Claim Adjustment Expenses Reserves Summary - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	$ 51,926
Discount (Net of Reinsurance)	(1,073)
Subtotal: Net Claims and Claim Adjustment Expense Reserves	50,853
Reinsurance Recoverables on Unpaid Losses	7,796
Claims and Claim Adjustment Expense Reserves	58,649	$ 56,907
Discount on reinsurance recoverables for long-term disability and annuity claim payments included in discount (net of reinsurance)	51
Reinsurance recoverables	8,063	8,452	$ 8,350
Property-casualty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	51,926
Discount (Net of Reinsurance)	(1,073)
Subtotal: Net Claims and Claim Adjustment Expense Reserves	50,853	48,688	46,357
Reinsurance Recoverables on Unpaid Losses	7,790	8,209	8,153	$ 8,035
Claims and Claim Adjustment Expense Reserves	58,643	56,897	$ 54,510	$ 51,836
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	6
Claims and Claim Adjustment Expense Reserves	6	$ 10
Business Insurance [Member] | General liability [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	9,269
Business Insurance [Member] | Commercial property [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	1,109
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	4,819
Business Insurance [Member] | Automobile [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	3,856
Business Insurance [Member] | Workers' compensation [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	16,473
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	2,388
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	564
Personal Insurance [Member] | Automobile [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	3,654
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	2,327
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	708
Reportable segments [Member] | Property-casualty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	45,167
Discount (Net of Reinsurance)	(1,069)
Subtotal: Net Claims and Claim Adjustment Expense Reserves	44,098
Reinsurance Recoverables on Unpaid Losses	3,275
Claims and Claim Adjustment Expense Reserves	47,373
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	9,269
Discount (Net of Reinsurance)	(135)
Subtotal: Net Claims and Claim Adjustment Expense Reserves	9,134
Reinsurance Recoverables on Unpaid Losses	949
Claims and Claim Adjustment Expense Reserves	10,083
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	1,109
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	1,109
Reinsurance Recoverables on Unpaid Losses	459
Claims and Claim Adjustment Expense Reserves	1,568
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	4,819
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	4,819
Reinsurance Recoverables on Unpaid Losses	219
Claims and Claim Adjustment Expense Reserves	5,038
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	3,856
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	3,856
Reinsurance Recoverables on Unpaid Losses	291
Claims and Claim Adjustment Expense Reserves	4,147
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	16,473
Discount (Net of Reinsurance)	(934)
Subtotal: Net Claims and Claim Adjustment Expense Reserves	15,539
Reinsurance Recoverables on Unpaid Losses	629
Claims and Claim Adjustment Expense Reserves	16,168
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	2,388
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	2,388
Reinsurance Recoverables on Unpaid Losses	204
Claims and Claim Adjustment Expense Reserves	2,592
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	564
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	564
Reinsurance Recoverables on Unpaid Losses	6
Claims and Claim Adjustment Expense Reserves	570
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	3,654
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	3,654
Reinsurance Recoverables on Unpaid Losses	390
Claims and Claim Adjustment Expense Reserves	4,044
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	2,327
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	2,327
Reinsurance Recoverables on Unpaid Losses	108
Claims and Claim Adjustment Expense Reserves	2,435
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	708
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	708
Reinsurance Recoverables on Unpaid Losses	20
Claims and Claim Adjustment Expense Reserves	728
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	4,187
Discount (Net of Reinsurance)	(4)
Subtotal: Net Claims and Claim Adjustment Expense Reserves	4,183
Reinsurance Recoverables on Unpaid Losses	1,786
Claims and Claim Adjustment Expense Reserves	5,969
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	2,481
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	2,481
Reinsurance Recoverables on Unpaid Losses	14
Claims and Claim Adjustment Expense Reserves	2,495
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	2,758
Claims and Claim Adjustment Expense Reserves	2,758
Reconciling Items [Member] | Other [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	91
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	91
Reinsurance Recoverables on Unpaid Losses	(43)
Claims and Claim Adjustment Expense Reserves	$ 48