Insurance Liabilities - Liability for Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Reconciliation of activity in the Liability for unpaid claims and claims adjustment expense:
Liability for unpaid loss and loss adjustment expenses, beginning of year	$ 69,168	$ 70,393
Reinsurance recoverable	(29,026)	(30,289)
Net Liability for unpaid loss and loss adjustment expenses, beginning of year	40,142	40,104
Losses and loss adjustment expenses incurred:
Current year	3,809	3,365
Prior years, excluding discount and amortization of deferred gain	(33)	0
Prior years, discount charge (benefit)	40	106
Prior years, amortization of deferred gain on retroactive reinsurance	(22)	(32)
Total losses and loss adjustment expenses incurred	3,794	3,439
Losses and loss adjustment expenses paid:
Current year	(429)	(286)
Prior years	(2,961)	(2,857)
Total losses and loss adjustment expenses paid	(3,390)	(3,143)
Other changes:
Foreign exchange effect	484	(496)
Losses and loss adjustment expenses recognized within gain on divestitures	32	0
Retroactive reinsurance adjustment (net of discount)	35	(8)
Reclassified to held for sale, net of reinsurance recoverables	0	(5)
Total other changes	551	(509)
Net liability for unpaid losses and loss adjustment expenses	41,097	39,891
Reinsurance recoverable	27,799	30,169
Total	68,896	70,060
Change in discount on loss reserves ceded under retroactive reinsurance	1	55
National Indemnity Company
Losses and loss adjustment expenses incurred:
Prior years, amortization of deferred gain on retroactive reinsurance	$ 5	$ 5