Claim and Claim Adjustment Expense Reserves (Reconciliation of claim and claim adjustment expense reserves) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 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	1,502	1,326
Increase (decrease) in provision for insured events of prior years	(6)	13
Amortization of discount	10	11
Total net incurred	1,506	1,350
Net payments attributable to:
Current year events	(113)	(72)
Prior year events	(1,168)	(1,042)
Total net payments	(1,281)	(1,114)
Foreign currency translation adjustment and other	(41)	35
Net reserves, end of period	18,347	17,200
Ceded reserves, end of period	5,241	5,209
Gross reserves, end of period	$ 23,588	$ 22,409