Unpaid losses and loss expenses Unpaid losses and loss expenses (Reconciliation of reserve Balances to Liability for Unpaid Loss)(Details) (Details) - 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 [Line Items]
Unpaid Loss and Allocated Loss Adjustment Expenses, Net		$ 53,940
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments		16,310
Short-duration Insurance Contracts, Liability for Unpaid Claims and Claim Adjustment Expense, Aggregate Reconciling Items	[1]	1,090
Unpaid unallocated loss adjustment expenses		1,603
Unpaid losses and loss expenses		72,943	$ 67,811	$ 62,690	$ 62,960
North America Commercial P&C Insurance - Workers' Compensation [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid Loss and Allocated Loss Adjustment Expenses, Net		9,942
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments		1,379
North America Commercial P&C Insurance - Liability [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid Loss and Allocated Loss Adjustment Expenses, Net		18,736
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments		6,263
North America Commercial P&C Insurance - Other Casualty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid Loss and Allocated Loss Adjustment Expenses, Net		2,304
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments		638
North America Commercial P&C Insurance - Non-Casualty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid Loss and Allocated Loss Adjustment Expenses, Net		2,963
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments		1,631
North America Personal P&C Insurance [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid Loss and Allocated Loss Adjustment Expenses, Net		3,035
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments		632
Overseas General Insurance - Casualty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid Loss and Allocated Loss Adjustment Expenses, Net		7,052
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments		2,363
Overseas General Insurance - Non-Casualty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid Loss and Allocated Loss Adjustment Expenses, Net		2,984
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments		1,868
Global Reinsurance - Casualty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid Loss and Allocated Loss Adjustment Expenses, Net		1,191
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments		33
Global Reinsurance - Non-Casualty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid Loss and Allocated Loss Adjustment Expenses, Net		372
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments		89
Other Segments [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid Loss and Allocated Loss Adjustment Expenses, Net		5,361
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments		$ 1,414

[1] Primarily includes the claims reserve of our International A&H business and Life Insurance segment reserves.