Claim and Claim Adjustment Expense Reserves (Reconciliation of Claim and Claim Adjustment Expense Reserves) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025
Reserves, beginning of year:
Gross	$ 26,599	$ 24,976
Ceded	5,982	5,713
Net reserves, beginning of year	20,617	19,263
Net incurred claim and claim adjustment expenses:
Provision for insured events of current year	3,534	3,309
Increase (decrease) in provision for insured events of prior years	192	189
Amortization of discount	19	20
Total net incurred	3,745	3,518
Net payments attributable to:
Current year events	(345)	(316)
Prior year events	(2,499)	(2,391)
Total net payments	(2,844)	(2,707)
Foreign currency translation adjustment and other	(70)	199
Net reserves, end of period	21,448	20,273
Ceded reserves, end of period	6,042	5,930
Gross reserves, end of period	$ 27,490	$ 26,203