Claim and Claim Adjustment Expense Reserves and Future Policy Benefit Reserves (Reconciliation of claim and claim adjustment expense reserves) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Reserves, beginning of year:
Gross	$ 24,174	$ 22,706
Ceded	4,969	4,005
Net reserves, beginning of year	19,205	18,701
Reduction of net reserves due to Excess Workers' Compensation Loss Portfolio Transfer	0	(632)
Net incurred claim and claim adjustment expenses:
Provision for insured events of current year	4,638	4,474
Increase (decrease) in provision for insured events of prior years	(144)	(130)
Amortization of discount	131	137
Total net incurred	4,625	4,481
Net payments attributable to:
Current year events	(523)	(629)
Prior year events	(3,371)	(2,874)
Total net payments	(3,894)	(3,503)
Foreign currency translation adjustment and other	(383)	(51)
Net reserves, end of period	19,553	18,996
Ceded reserves, end of period	5,147	4,836
Gross reserves, end of period	$ 24,700	$ 23,832