Insurance Liabilities - Liability for Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Reconciliation of activity in the Liability for unpaid claims and claims adjustment expense:
Liability for unpaid loss and loss adjustment expenses, beginning of period	$ 70,060	$ 75,793	$ 70,393	$ 75,167
Reinsurance recoverable	(30,169)	(32,366)	(30,289)	(32,102)
Net Liability for unpaid loss and loss adjustment expenses, beginning of period	39,891	43,427	40,104	43,065
Losses and loss adjustment expenses incurred:
Current year	3,546	3,945	6,911	7,729
Prior years, excluding discount and amortization of deferred gain	(108)	(107)	(108)	(134)
Prior years, discount charge (benefit)	62	54	168	148
Prior years, amortization of deferred gain on retroactive reinsurance	(33)	(25)	(65)	(85)
Total losses and loss adjustment expenses incurred	3,467	3,867	6,906	7,658
Losses and loss adjustment expenses paid:
Current year	(855)	(881)	(1,141)	(1,170)
Prior years	(2,597)	(2,994)	(5,454)	(6,543)
Total losses and loss adjustment expenses paid	(3,452)	(3,875)	(6,595)	(7,713)
Other changes:
Foreign exchange effect	(158)	(25)	(654)	372
Retroactive reinsurance adjustment (net of discount)	186	47	178	59
Reclassified to held for sale, net of reinsurance recoverables	0	(3,383)	(5)	(3,383)
Total other changes	28	(3,361)	(481)	(2,952)
Net liability for unpaid losses and loss adjustment expenses	39,934	40,058	39,934	40,058
Reinsurance recoverable	29,849	30,226	29,849	30,226
Total	69,783	70,284	69,783	70,284
Change in discount on loss reserves ceded under retroactive reinsurance	23	26	78	96
Assets and Liabilities Held for Sale
Other changes:
Reinsurance recoverable		1,500		1,500
National Indemnity Company
Losses and loss adjustment expenses incurred:
Prior years, amortization of deferred gain on retroactive reinsurance	$ 39	$ 6	$ 44	$ 13