Claim and Claim Adjustment Expense Reserves (Reconciliation of Claim and Claim Adjustment Expense Reserves) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
Reserves, beginning of year:
Gross	$ 24,976	$ 23,304
Ceded	5,713	5,141
Net reserves, beginning of year	19,263	18,163
Net incurred claim and claim adjustment expenses:
Provision for insured events of current year	5,011	4,706
Increase (decrease) in provision for insured events of prior years	191	26
Amortization of discount	29	30
Total net incurred	5,231	4,762
Net payments attributable to:
Current year events	(659)	(655)
Prior year events	(3,463)	(3,189)
Total net payments	(4,122)	(3,844)
Foreign currency translation adjustment and other	165	35
Net reserves, end of period	20,537	19,116
Ceded reserves, end of period	5,988	5,442
Gross reserves, end of period	$ 26,525	$ 24,558