Unpaid losses and loss expenses (RF) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2024	Mar. 31, 2023
Unpaid Losses and Loss Expenses [Roll Forward]
Gross unpaid losses and loss expenses – beginning of period		$ 80,122	$ 75,747
Reinsurance recoverable on unpaid losses – beginning of period (1)	[1]	(17,884)	(17,086)
Net unpaid losses and loss expenses – beginning of period		62,238	58,661
Current Year Claims and Claims Adjustment Expense		5,980	5,336
Prior Year Claims and Claims Adjustment Expense	[2]	(253)	(188)
Total, Incurred		5,727	5,148
Net loss and loss expenses paid, Current Year		767	805
Net loss and loss expenses paid, Prior Years		4,055	3,911
Total, Paid		4,822	4,716
Liability For Unpaid Claims And Claims Adjustment Expense Foreign Currency Revaluation And Other		35	(196)
Net unpaid losses and loss expenses – end of period		63,178	58,897
Reinsurance recoverable on unpaid losses (1)	[1]	17,163	16,520
Gross unpaid losses and loss expenses – end of period		80,341	75,417
prior period development, net adjustments		46	$ (8)
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)		$ 940

[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 A&H long-duration lines totaling $46 million and $(8) million for the three months ended March 31, 2024 and 2023, respectively.