Insurance Claim Reserves (Details) - Claims and Claim Adjustment Expenses Reserves Summary - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	$ 49,779
Discount (Net of Reinsurance)	(1,091)
Subtotal: Net Claims and Claim Adjustment Expense Reserves	48,688
Reinsurance Recoverables on Unpaid Losses	8,219
Claims and Claim Adjustment Expense Reserves	56,907	$ 54,521
Discount on reinsurance recoverables for long-term disability and annuity claim payments included in discount (net of reinsurance)	55
Reinsurance recoverables	8,452	8,350	$ 8,235
Property-casualty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	49,779
Discount (Net of Reinsurance)	(1,091)
Subtotal: Net Claims and Claim Adjustment Expense Reserves	48,688	46,357	43,801	$ 42,471
Reinsurance Recoverables on Unpaid Losses	8,209	8,153	8,035	8,182
Claims and Claim Adjustment Expense Reserves	56,897	54,510	$ 51,836	$ 50,653
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	10
Claims and Claim Adjustment Expense Reserves	10	$ 11
Business Insurance [Member] | General liability [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	8,893
Business Insurance [Member] | Commercial property [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	997
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	4,427
Business Insurance [Member] | Automobile [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	3,740
Business Insurance [Member] | Workers' compensation [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	16,623
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	2,297
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	527
Personal Insurance [Member] | Automobile [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	3,155
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	1,661
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	745
Reportable segments [Member] | Property-casualty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	43,065
Discount (Net of Reinsurance)	(1,087)
Subtotal: Net Claims and Claim Adjustment Expense Reserves	41,978
Reinsurance Recoverables on Unpaid Losses	3,536
Claims and Claim Adjustment Expense Reserves	45,514
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	8,893
Discount (Net of Reinsurance)	(139)
Subtotal: Net Claims and Claim Adjustment Expense Reserves	8,754
Reinsurance Recoverables on Unpaid Losses	978
Claims and Claim Adjustment Expense Reserves	9,732
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	997
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	997
Reinsurance Recoverables on Unpaid Losses	513
Claims and Claim Adjustment Expense Reserves	1,510
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	4,427
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	4,427
Reinsurance Recoverables on Unpaid Losses	225
Claims and Claim Adjustment Expense Reserves	4,652
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	3,740
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	3,740
Reinsurance Recoverables on Unpaid Losses	303
Claims and Claim Adjustment Expense Reserves	4,043
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	16,623
Discount (Net of Reinsurance)	(948)
Subtotal: Net Claims and Claim Adjustment Expense Reserves	15,675
Reinsurance Recoverables on Unpaid Losses	665
Claims and Claim Adjustment Expense Reserves	16,340
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	2,297
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	2,297
Reinsurance Recoverables on Unpaid Losses	173
Claims and Claim Adjustment Expense Reserves	2,470
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	527
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	527
Reinsurance Recoverables on Unpaid Losses	6
Claims and Claim Adjustment Expense Reserves	533
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	3,155
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	3,155
Reinsurance Recoverables on Unpaid Losses	442
Claims and Claim Adjustment Expense Reserves	3,597
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	1,661
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	1,661
Reinsurance Recoverables on Unpaid Losses	210
Claims and Claim Adjustment Expense Reserves	1,871
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	745
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	745
Reinsurance Recoverables on Unpaid Losses	21
Claims and Claim Adjustment Expense Reserves	766
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	4,231
Discount (Net of Reinsurance)	(4)
Subtotal: Net Claims and Claim Adjustment Expense Reserves	4,227
Reinsurance Recoverables on Unpaid Losses	1,825
Claims and Claim Adjustment Expense Reserves	6,052
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	2,383
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	2,383
Reinsurance Recoverables on Unpaid Losses	15
Claims and Claim Adjustment Expense Reserves	2,398
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	2,856
Claims and Claim Adjustment Expense Reserves	2,856
Reconciling Items [Member] | Other [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Net Undiscounted Claims and Claim Adjustment Expense Reserves	100
Discount (Net of Reinsurance)	0
Subtotal: Net Claims and Claim Adjustment Expense Reserves	100
Reinsurance Recoverables on Unpaid Losses	(23)
Claims and Claim Adjustment Expense Reserves	$ 77