Claim, Claim Adjustment Expense and Future Policy Benefit Reserves, Net Prior Year Loss Reserve Development in Property and Casualty Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net Prior Year Development [Abstract]
Pretax favorable development	$ 11	$ (20)	$ (73)
Medical Professional Liability
Net Prior Year Development [Abstract]
Pretax favorable development	23	35	75
Other Professional Liability and Management Liability
Net Prior Year Development [Abstract]
Pretax favorable development	24	(15)	(69)
Surety
Net Prior Year Development [Abstract]
Pretax favorable development	(73)	(69)	(92)
Commercial Auto
Net Prior Year Development [Abstract]
Pretax favorable development	53	33	(25)
General Liability
Net Prior Year Development [Abstract]
Pretax favorable development	15	15	16
Workers' Compensation
Net Prior Year Development [Abstract]
Pretax favorable development	(82)	(96)	(13)
Property and Other
Net Prior Year Development [Abstract]
Pretax favorable development	(9)	27	(3)
Other insurance operations
Net Prior Year Development [Abstract]
Pretax favorable development	$ 60	$ 50	$ 38