Unpaid losses and loss expenses (RF) (Details) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2023	Jun. 30, 2022
Unpaid Losses and Loss Expenses [Roll Forward]
Gross unpaid losses and loss expenses – beginning of period		$ 75,747	$ 72,330
Reinsurance recoverable on unpaid losses – beginning of period (1)	[1]	(17,086)	(16,132)
Net unpaid losses and loss expenses – beginning of period		58,661	56,198
Current Year Claims and Claims Adjustment Expense		11,227	10,391
Prior Year Claims and Claims Adjustment Expense	[2]	(396)	(621)
Total, Incurred		10,831	9,770
Net loss and loss expenses paid, Current Year		2,264	1,881
Net loss and loss expenses paid, Prior Years		7,527	6,566
Total, Paid		9,791	8,447
Liability For Unpaid Claims And Claims Adjustment Expense Foreign Currency Revaluation And Other		171	(577)
Net unpaid losses and loss expenses – end of period		59,872	56,944
Reinsurance recoverable on unpaid losses (1)	[1]	16,608	16,504
Gross unpaid losses and loss expenses – end of period		76,480	73,448
prior period development, net adjustments		0	$ 134
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease), Gross		733
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)		$ 1,200

[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 $0 million and $134 million for the six months ended June 30, 2023 and 2022, respectively.