Insurance Liabilities - Liability for unpaid losses and loss adjustment expenses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Reconciliation of activity in the Liability for unpaid claims and claims adjustment expense:
Liability for unpaid loss and loss adjustment expenses, beginning of year	$ 79,026	$ 77,720	$ 78,328
Reinsurance recoverable	(35,213)	(34,431)	(31,069)
Initial allowance upon CECL adoption			164
Net Liability for unpaid loss and loss adjustment expenses, beginning of year	43,813	43,289	47,423
Losses and loss adjustment expenses incurred:
Current year	16,434	16,434	16,928
Prior years, excluding discount and amortization of deferred gain	(530)	(171)	(90)
Prior years, discount charge (benefit)	(605)	(131)	587
Prior years, amortization of deferred gain on retroactive reinsurance	(252)	(190)	(237)
Total losses and loss adjustment expenses incurred	15,047	15,942	17,188
Losses and loss adjustment expenses paid:
Current year	(4,011)	(3,868)	(4,062)
Prior years	(11,066)	(11,503)	(14,603)
Total losses and loss adjustment expenses paid	(15,077)	(15,371)	(18,665)
Other changes:
Foreign exchange effect	(1,463)	(593)	815
Allowance for credit losses	0	0	(15)
Retroactive reinsurance adjustment (net of discount)	745	546	361
Fortitude sale	0	0	3,818
Total other changes	(718)	(47)	(2,657)
Net liability for unpaid losses and loss adjustment expenses	43,065	43,813	43,289
Reinsurance recoverable	32,102	35,213	34,431
Total	75,167	79,026	77,720
Change in discount on loss reserves ceded under retroactive reinsurance	(301)	(42)	340
National Indemnity Company
Losses and loss adjustment expenses incurred:
Prior years, amortization of deferred gain on retroactive reinsurance	$ 63	$ 53	$ 41