Unpaid losses and loss expenses (RF) (Details) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2023	Sep. 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		18,604	17,755
Prior Year Claims and Claims Adjustment Expense	[2]	(667)	(922)
Total, Incurred		17,937	16,833
Net loss and loss expenses paid, Current Year		4,853	4,511
Net loss and loss expenses paid, Prior Years		10,158	9,217
Total, Paid		15,011	13,728
Liability For Unpaid Claims And Claims Adjustment Expense Foreign Currency Revaluation And Other		(95)	(1,280)
Net unpaid losses and loss expenses – end of period		61,897	58,023
Reinsurance recoverable on unpaid losses (1)	[1]	17,808	17,313
Gross unpaid losses and loss expenses – end of period		79,705	75,336
prior period development, net adjustments		71	$ 213
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease), Gross		4,000
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)		$ 3,200

[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 $71 million and $213 million for the nine months ended September 30, 2023 and 2022, respectively.