Claim and Claim Adjustment Expense Reserves - Reconciliation of Claim and Claim Adjustment Expense Reserves (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross reserves, beginning of year	$ 23,304	$ 22,120	$ 21,269
Ceded reserves, beginning of year	5,141	5,191	4,969
Net reserves, beginning of year	18,163	16,929	16,300
Net incurred claim and claim adjustment expenses:
Provision for insured events of current year	6,330	5,667	5,181
Increase (decrease) in provision for insured events of prior years	42	48	(32)
Amortization of discount	39	44	44
Total net incurred	6,411	5,759	5,193
Net payments attributable to:
Current year events	(1,093)	(922)	(821)
Prior year events	(4,096)	(3,679)	(3,481)
Total net payments	(5,189)	(4,601)	(4,302)
Foreign currency translation adjustment and other	(122)	76	(262)
Net reserves, end of year	19,263	18,163	16,929
Ceded reserves, end of year	5,713	5,141	5,191
Gross reserves, end of year	$ 24,976	$ 23,304	$ 22,120