Unpaid losses and loss expenses (RF) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2022	Mar. 31, 2021
Unpaid Losses and Loss Expenses [Roll Forward]
Gross unpaid losses and loss expenses – beginning of period		$ 72,943	$ 67,811
Reinsurance recoverable on unpaid losses – beginning of period (1)	[1]	(16,184)	(14,647)
Net unpaid losses and loss expenses – beginning of period		56,759	53,164
Current Year Claims and Claims Adjustment Expense		5,192	5,249
Prior Year Claims and Claims Adjustment Expense	[2]	(405)	(196)
Total, Incurred		4,787	5,053
Net loss and loss expenses paid, Current Year		792	732
Net loss and loss expenses paid, Prior Years		3,569	3,161
Total, Paid		4,361	3,893
Liability For Unpaid Claims And Claims Adjustment Expense Foreign Currency Revaluation And Other		13	71
Net unpaid losses and loss expenses – end of period		57,198	54,395
Reinsurance recoverable on unpaid losses (1)	[1]	16,646	14,860
Gross unpaid losses and loss expenses – end of period		73,844	69,255
prior period development, net adjustments		165	$ 4
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease), Gross		901
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)		$ 439

[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 and earned premiums totaling $165 million and $4 million for the three months ended March 31, 2022 and 2021, respectively.