Claim, Claim Adjustment Expense and Future Policy Benefit Reserves (Reconciliation of Claim and Claim Adjustment Expense Reserves) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reserves, beginning of year:
Gross	$ 22,706	$ 21,720	$ 21,984
Ceded	4,005	3,835	4,019
Net reserves, beginning of year	18,701	17,885	17,965
Reduction of net reserves due to Excess Workers' Compensation Loss Portfolio Transfer	(632)	0	0
Net incurred claim and claim adjustment expenses:
Provision for insured events of current year	5,970	5,793	5,356
Increase (decrease) in provision for insured events of prior years	(104)	(119)	(127)
Amortization of discount	174	183	184
Total net incurred	6,040	5,857	5,413
Net payments attributable to:
Current year events	(1,014)	(948)	(992)
Prior year events	(3,830)	(4,216)	(4,584)
Total net payments	(4,844)	(5,164)	(5,576)
Foreign currency translation adjustment and other	(60)	123	83
Net reserves, end of year	19,205	18,701	17,885
Ceded reserves, end of year	4,969	4,005	3,835
Gross reserves, end of year	$ 24,174	$ 22,706	$ 21,720