Insurance Liabilities - Liability for Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Reconciliation of activity in the Liability for unpaid claims and claims adjustment expense:
Liability for unpaid loss and loss adjustment expenses, beginning of period	$ 69,754	$ 69,783	$ 69,168	$ 70,393
Reinsurance recoverable	(27,866)	(29,849)	(29,026)	(30,289)
Net Liability for unpaid loss and loss adjustment expenses, beginning of period	41,888	39,934	40,142	40,104
Losses and loss adjustment expenses incurred:
Current year	3,572	3,749	10,904	10,660
Prior years, excluding discount and amortization of deferred gain	(161)	187	(169)	79
Prior years, discount charge (benefit)	34	49	119	217
Prior years, amortization of deferred gain on retroactive reinsurance	(54)	(212)	(176)	(277)
Total losses and loss adjustment expenses incurred	3,391	3,773	10,678	10,679
Losses and loss adjustment expenses paid:
Current year	(1,262)	(1,169)	(2,714)	(2,310)
Prior years	(2,371)	(2,285)	(7,901)	(7,739)
Total losses and loss adjustment expenses paid	(3,633)	(3,454)	(10,615)	(10,049)
Other changes:
Foreign exchange effect	(102)	891	1,277	237
Losses and loss adjustment expenses recognized within gain on divestitures	13	0	60	0
Retroactive reinsurance adjustment (net of discount)	77	(107)	92	71
Dispositions	0	(5)	0	(5)
Reclassified to held for sale, net of reinsurance recoverables	0	5	0	0
Total other changes	(12)	784	1,429	303
Net liability for unpaid losses and loss adjustment expenses	41,634	41,037	41,634	41,037
Reinsurance recoverable	28,248	30,029	28,248	30,029
Total	69,882	71,066	69,882	71,066
Change in discount on loss reserves ceded under retroactive reinsurance	7	22	27	100
National Indemnity Company
Losses and loss adjustment expenses incurred:
Prior years, amortization of deferred gain on retroactive reinsurance	$ 14	$ 3	$ 26	$ 47