Claim and Claim Adjustment Expense Reserves 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, 2022	Dec. 31, 2021	Dec. 31, 2020
Net Prior Year Development [Abstract]
Pretax favorable development	$ (32)	$ 11	$ (20)
Medical Professional Liability
Net Prior Year Development [Abstract]
Pretax favorable development	18	23	35
Other Professional Liability and Management Liability
Net Prior Year Development [Abstract]
Pretax favorable development	50	24	(15)
Surety
Net Prior Year Development [Abstract]
Pretax favorable development	(83)	(73)	(69)
Commercial Auto
Net Prior Year Development [Abstract]
Pretax favorable development	49	53	33
General Liability
Net Prior Year Development [Abstract]
Pretax favorable development	67	15	15
Workers' Compensation
Net Prior Year Development [Abstract]
Pretax favorable development	(152)	(82)	(96)
Property and Other
Net Prior Year Development [Abstract]
Pretax favorable development	(45)	(9)	27
Other Insurance Operations
Net Prior Year Development [Abstract]
Pretax favorable development	$ 64	$ 60	$ 50