Claim and Claim Adjustment Expense Reserves (Reconciliation of claim and claim adjustment expense reserves) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Reserves, beginning of year:
Gross	$ 22,120	$ 21,269
Ceded	5,191	4,969
Net reserves, beginning of year	16,929	16,300
Net incurred claim and claim adjustment expenses:
Provision for insured events of current year	4,221	3,830
Increase (decrease) in provision for insured events of prior years	43	(4)
Amortization of discount	33	33
Total net incurred	4,297	3,859
Net payments attributable to:
Current year events	(588)	(482)
Prior year events	(2,953)	(2,700)
Total net payments	(3,541)	(3,182)
Foreign currency translation adjustment and other	(30)	(383)
Net reserves, end of period	17,655	16,594
Ceded reserves, end of period	5,181	5,147
Gross reserves, end of period	$ 22,836	$ 21,741