Claim and Claim Adjustment Expense Reserves (Reconciliation of claim and claim adjustment expense reserves) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Reserves, beginning of year:
Gross	$ 23,304	$ 22,120
Ceded	5,141	5,191
Net reserves, beginning of year	18,163	16,929
Net incurred claim and claim adjustment expenses:
Provision for insured events of current year	4,706	4,221
Increase (decrease) in provision for insured events of prior years	26	43
Amortization of discount	30	33
Total net incurred	4,762	4,297
Net payments attributable to:
Current year events	(655)	(588)
Prior year events	(3,189)	(2,953)
Total net payments	(3,844)	(3,541)
Foreign currency translation adjustment and other	35	(30)
Net reserves, end of period	19,116	17,655
Ceded reserves, end of period	5,442	5,181
Gross reserves, end of period	$ 24,558	$ 22,836