Insurance Liabilities - Liability for Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Reconciliation of activity in the Liability for unpaid claims and claims adjustment expense:
Liability for unpaid loss and loss adjustment expenses, beginning of year	$ 70,393	$ 75,167	$ 79,026
Reinsurance recoverable	(30,289)	(32,102)	(35,213)
Net Liability for unpaid loss and loss adjustment expenses, beginning of year	40,104	43,065	43,813
Losses and loss adjustment expenses incurred:
Current year	14,363	15,100	16,434
Prior years, excluding discount and amortization of deferred gain	254	(392)	(530)
Prior years, discount charge (benefit)	354	307	(605)
Prior years, amortization of deferred gain on retroactive reinsurance	(404)	(81)	(252)
Total losses and loss adjustment expenses incurred	14,567	14,934	15,047
Losses and loss adjustment expenses paid:
Current year	(3,694)	(3,836)	(4,011)
Prior years	(9,849)	(11,868)	(11,066)
Total losses and loss adjustment expenses paid	(13,543)	(15,704)	(15,077)
Other changes:
Foreign exchange effect	(996)	606	(1,463)
Losses and loss adjustment expenses recognized within gain on divestitures	0	569	0
Retroactive reinsurance adjustment (net of discount)	15	158	745
Dispositions	(5)	(3,505)	0
Reclassified to held for sale, net of reinsurance recoverables	0	(19)	0
Total other changes	(986)	(2,191)	(718)
Net liability for unpaid losses and loss adjustment expenses	40,142	40,104	43,065
Reinsurance recoverable	29,026	30,289	32,102
Total	69,168	70,393	75,167
Change in discount on loss reserves ceded under retroactive reinsurance	168	150	(301)
National Indemnity Company
Losses and loss adjustment expenses incurred:
Prior years, amortization of deferred gain on retroactive reinsurance	$ 82	$ 33	$ 63