Unpaid losses and loss expenses (RF) (Details) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
		Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Unpaid Losses and Loss Expenses [Roll Forward]
Gross unpaid losses and loss expenses – beginning of period		$ 75,747	$ 72,330	$ 72,330
Reinsurance recoverable on unpaid losses – beginning of period (1)	[1]	(17,086)	(16,132)	(16,132)
Net unpaid losses and loss expenses – beginning of period		58,661	56,198	56,198
Current Year Claims and Claims Adjustment Expense		5,336	4,963
Prior Year Claims and Claims Adjustment Expense	[2]	(188)	(399)
Total, Incurred		5,148	4,564
Net loss and loss expenses paid, Current Year		805	593
Net loss and loss expenses paid, Prior Years		3,911	3,569
Total, Paid		4,716	4,162
Liability For Unpaid Claims And Claims Adjustment Expense Foreign Currency Revaluation And Other		(196)	3
Net unpaid losses and loss expenses – end of period		58,897	56,603	58,661
Reinsurance recoverable on unpaid losses (1)	[1]	16,520	16,593	17,086
Gross unpaid losses and loss expenses – end of period		75,417	73,196	$ 75,747
prior period development, net adjustments		(8)	$ 159
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease), Gross		(330)
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)		$ 236

[1] Net of valuation allowance for uncollectible reinsurance.

[2] Relates to prior period loss reserve development only and excludes prior period development related to reinstatement premiums, expense adjustments, earned premiums, and development on international A&H lines totaling $(8) million and $159 million for the three months ended March 31, 2023 and 2022, respectively.