Insurance Liabilities - Liability for Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 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	$ 68,896	$ 70,060	$ 69,168	$ 70,393
Reinsurance recoverable	(27,799)	(30,169)	(29,026)	(30,289)
Net Liability for unpaid loss and loss adjustment expenses, beginning of period	41,097	39,891	40,142	40,104
Losses and loss adjustment expenses incurred:
Current year	3,523	3,546	7,332	6,911
Prior years, excluding discount and amortization of deferred gain	25	(108)	(8)	(108)
Prior years, discount charge (benefit)	45	62	85	168
Prior years, amortization of deferred gain on retroactive reinsurance	(100)	(33)	(122)	(65)
Total losses and loss adjustment expenses incurred	3,493	3,467	7,287	6,906
Losses and loss adjustment expenses paid:
Current year	(1,023)	(855)	(1,452)	(1,141)
Prior years	(2,569)	(2,597)	(5,530)	(5,454)
Total losses and loss adjustment expenses paid	(3,592)	(3,452)	(6,982)	(6,595)
Other changes:
Foreign exchange effect	895	(158)	1,379	(654)
Losses and loss adjustment expenses recognized within gain on divestitures	15	0	47	0
Retroactive reinsurance adjustment (net of discount)	(20)	186	15	178
Reclassified to held for sale, net of reinsurance recoverables	0	0	0	(5)
Total other changes	890	28	1,441	(481)
Net liability for unpaid losses and loss adjustment expenses	41,888	39,934	41,888	39,934
Reinsurance recoverable	27,866	29,849	27,866	29,849
Total	69,754	69,783	69,754	69,783
Change in discount on loss reserves ceded under retroactive reinsurance	19	23	20	78
National Indemnity Company
Losses and loss adjustment expenses incurred:
Prior years, amortization of deferred gain on retroactive reinsurance	$ 7	$ 39	$ 12	$ 44