Unpaid losses and loss expenses (RF) (Details) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2022	Jun. 30, 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		10,846	10,546
Prior Year Claims and Claims Adjustment Expense	[2]	(651)	(487)
Total, Incurred		10,195	10,059
Net loss and loss expenses paid, Current Year		2,281	2,355
Net loss and loss expenses paid, Prior Years		6,566	5,531
Total, Paid		8,847	7,886
Liability For Unpaid Claims And Claims Adjustment Expense Foreign Currency Revaluation And Other		(588)	231
Net unpaid losses and loss expenses – end of period		57,519	55,568
Reinsurance recoverable on unpaid losses (1)	[1]	16,573	14,721
Gross unpaid losses and loss expenses – end of period		74,092	70,289
prior period development, net adjustments		164	$ 27
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease), Gross		1,149
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)		$ 760

[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 $164 million and $27 million for the six months ended June 30, 2022 and 2021, respectively.