Unpaid losses and loss expenses Unpaid losses and loss expenses (Reconciliation of reserve Balances to Liability for Unpaid Loss) (Details) - 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 [Line Items]
Net Unpaid Loss and Allocated Loss Adjustment Expense		$ 56,389
Ceded unpaid loss and allocated loss adjustment expense		17,314
Unpaid loss and loss expense on other than short-duration contracts	[1]	943
Unpaid unallocated loss adjustment expenses		1,677
Unpaid losses and loss expenses		76,323	$ 72,943	$ 67,811	$ 62,690
North America Commercial P&C Insurance - Workers' Compensation [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net Unpaid Loss and Allocated Loss Adjustment Expense		9,962
Ceded unpaid loss and allocated loss adjustment expense		1,274
North America Commercial P&C Insurance - Liability [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net Unpaid Loss and Allocated Loss Adjustment Expense		20,014
Ceded unpaid loss and allocated loss adjustment expense		6,920
North America Commercial P&C Insurance - Other Casualty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net Unpaid Loss and Allocated Loss Adjustment Expense		2,530
Ceded unpaid loss and allocated loss adjustment expense		888
North America Commercial P&C Insurance - Non-Casualty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net Unpaid Loss and Allocated Loss Adjustment Expense		3,253
Ceded unpaid loss and allocated loss adjustment expense		1,883
North America Personal P&C Insurance [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net Unpaid Loss and Allocated Loss Adjustment Expense		3,225
Ceded unpaid loss and allocated loss adjustment expense		530
Overseas General Insurance - Casualty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net Unpaid Loss and Allocated Loss Adjustment Expense		7,287
Ceded unpaid loss and allocated loss adjustment expense		2,481
Overseas General Insurance - Non-Casualty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net Unpaid Loss and Allocated Loss Adjustment Expense		3,206
Ceded unpaid loss and allocated loss adjustment expense		1,702
Global Reinsurance - Casualty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net Unpaid Loss and Allocated Loss Adjustment Expense		1,208
Ceded unpaid loss and allocated loss adjustment expense		55
Global Reinsurance - Non-Casualty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net Unpaid Loss and Allocated Loss Adjustment Expense		494
Ceded unpaid loss and allocated loss adjustment expense		171
Other Segments [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net Unpaid Loss and Allocated Loss Adjustment Expense		5,210
Ceded unpaid loss and allocated loss adjustment expense		$ 1,410

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