Claim and Claim Adjustment Expense Reserves (Reconciliation of claim and claim adjustment expense reserves) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2023	Jun. 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	2,746	2,452
Increase (decrease) in provision for insured events of prior years	37	30
Amortization of discount	22	22
Total net incurred	2,805	2,504
Net payments attributable to:
Current year events	(287)	(233)
Prior year events	(2,014)	(1,882)
Total net payments	(2,301)	(2,115)
Foreign currency translation adjustment and other	57	(222)
Net reserves, end of period	17,490	16,467
Ceded reserves, end of period	5,312	5,156
Gross reserves, end of period	$ 22,802	$ 21,623