Insurance Liabilities - Liability for Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Reconciliation of activity in the Liability for unpaid claims and claims adjustment expense:
Liability for unpaid loss and loss adjustment expenses, beginning of year	$ 70,666	$ 69,168
Reinsurance recoverable	(28,871)	(29,026)
Net Liability for unpaid loss and loss adjustment expenses, beginning of year	41,795	40,142
Losses and loss adjustment expenses incurred:
Current year	3,661	3,809
Prior years, excluding discount and amortization of deferred gain	(126)	(33)
Prior years, discount charge (benefit)	(25)	40
Prior years, amortization of deferred gain on retroactive reinsurance	(35)	(22)
Total losses and loss adjustment expenses incurred	3,475	3,794
Losses and loss adjustment expenses paid:
Current year	(480)	(429)
Prior years	(2,853)	(2,961)
Total losses and loss adjustment expenses paid	(3,333)	(3,390)
Other changes:
Foreign exchange effect	(194)	484
Losses and loss adjustment expenses recognized within net (gain) loss on divestitures	4	32
Retroactive reinsurance adjustment (net of discount)	18	35
Total other changes	(172)	551
Net liability for unpaid losses and loss adjustment expenses	41,765	41,097
Reinsurance recoverable	28,198	27,799
Total	69,963	68,896
Change in discount on loss reserves ceded under retroactive reinsurance	53	1
National Indemnity Company
Losses and loss adjustment expenses incurred:
Prior years, amortization of deferred gain on retroactive reinsurance	$ 15	$ 5