Claim and Claim Adjustment Expense Reserves and Future Policy Benefit Reserves (Reconciliation of Claim and Claim Adjustment Expense Reserves) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Reserves, beginning of year:
Gross	$ 24,174	$ 22,706	$ 21,720
Ceded	4,969	4,005	3,835
Net reserves, beginning of year	19,205	18,701	17,885
Reduction of net reserves due to Excess Workers' Compensation Loss Portfolio Transfer	0	(632)	0
Net incurred claim and claim adjustment expenses:
Provision for insured events of current year	6,243	5,970	5,793
Increase (decrease) in provision for insured events of prior years	(187)	(104)	(119)
Amortization of discount	170	174	183
Total net incurred	6,226	6,040	5,857
Net payments attributable to:
Current year events	(913)	(1,014)	(948)
Prior year events	(4,348)	(3,830)	(4,216)
Total net payments	(5,261)	(4,844)	(5,164)
Foreign currency translation adjustment and other	(262)	(60)	123
Net reserves, end of year	19,908	19,205	18,701
Ceded reserves, end of year	5,191	4,969	4,005
Gross reserves, end of year	$ 25,099	$ 24,174	$ 22,706