Insurance Liabilities - Liability for Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Reconciliation of activity in the Liability for unpaid claims and claims adjustment expense:
Liability for unpaid loss and loss adjustment expenses, beginning of period	$ 69,783	$ 70,284	$ 70,393	$ 75,167
Reinsurance recoverable	(29,849)	(30,226)	(30,289)	(32,102)
Net Liability for unpaid loss and loss adjustment expenses, beginning of period	39,934	40,058	40,104	43,065
Losses and loss adjustment expenses incurred:
Current year	3,749	3,922	10,660	11,651
Prior years, excluding discount and amortization of deferred gain	187	(246)	79	(380)
Prior years, discount charge (benefit)	49	52	217	200
Prior years, amortization of deferred gain on retroactive reinsurance	(212)	27	(277)	(58)
Total losses and loss adjustment expenses incurred	3,773	3,755	10,679	11,413
Losses and loss adjustment expenses paid:
Current year	(1,169)	(1,190)	(2,310)	(2,360)
Prior years	(2,285)	(2,561)	(7,739)	(9,104)
Total losses and loss adjustment expenses paid	(3,454)	(3,751)	(10,049)	(11,464)
Other changes:
Foreign exchange effect	891	(583)	237	(211)
Losses and loss adjustment expenses recognized within gain on divestitures	0	316	0	316
Retroactive reinsurance adjustment (net of discount)	(107)	121	71	180
Dispositions	(5)	0	(5)	0
Reclassified to held for sale, net of reinsurance recoverables	5	(159)	0	(3,542)
Total other changes	784	(305)	303	(3,257)
Net liability for unpaid losses and loss adjustment expenses	41,037	39,757	41,037	39,757
Reinsurance recoverable	30,029	30,066	30,029	30,066
Total	71,066	69,823	71,066	69,823
Change in discount on loss reserves ceded under retroactive reinsurance	22	24	100	120
Assets and Liabilities Held for Sale
Other changes:
Reinsurance recoverable		1,500		1,500
National Indemnity Company
Losses and loss adjustment expenses incurred:
Prior years, amortization of deferred gain on retroactive reinsurance	$ 3	$ 9	$ 47	$ 22