Insurance Liabilities - Liability for unpaid losses and loss adjustment expenses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Reconciliation of activity in the Liability for unpaid claims and claims adjustment expense:
Liability for unpaid loss and loss adjustment expenses, beginning of period	$ 70,284	$ 76,739	$ 75,167	$ 79,026
Reinsurance recoverable	(30,226)	(33,583)	(32,102)	(35,213)
Net Liability for unpaid loss and loss adjustment expenses, beginning of period	40,058	43,156	43,065	43,813
Losses and loss adjustment expenses incurred:
Current year	3,922	4,373	11,651	12,020
Prior years, excluding discount and amortization of deferred gain	(246)	(112)	(380)	(537)
Prior years, discount charge (benefit)	52	36	200	78
Prior years, amortization of deferred gain on retroactive reinsurance	27	(23)	(58)	(37)
Total losses and loss adjustment expenses incurred	3,755	4,274	11,413	11,524
Losses and loss adjustment expenses paid:
Current year	(1,190)	(1,132)	(2,360)	(2,289)
Prior years	(2,561)	(2,673)	(9,104)	(8,844)
Total losses and loss adjustment expenses paid	(3,751)	(3,805)	(11,464)	(11,133)
Other changes:
Foreign exchange effect	(583)	(1,031)	(211)	(1,827)
Losses and loss adjustment expenses recognized within gain on divestitures	316	0	316	0
Retroactive reinsurance adjustment (net of discount)	121	101	180	318
Reclassified to held for sale, net of reinsurance recoverables	(159)	0	(3,542)	0
Total other changes	(305)	(930)	(3,257)	(1,509)
Net liability for unpaid losses and loss adjustment expenses	39,757	42,695	39,757	42,695
Reinsurance recoverable(c)	30,066	32,824	30,066	32,824
Total	69,823	75,519	69,823	75,519
Change in discount on loss reserves ceded under retroactive reinsurance	24	17	120	74
Reclassified to Assets
Other changes:
Reinsurance recoverable(c)		1,500		1,500
National Indemnity Company
Losses and loss adjustment expenses incurred:
Prior years, amortization of deferred gain on retroactive reinsurance	$ 9	$ 5	$ 22	$ 15