Claim and Claim Adjustment Expense Reserves - Net Prior Year Loss Reserve Development in Property and Casualty Operations (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	$ 13	$ (12)
Medical professional liability
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	9	8
Surety
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development		(9)
Workers’ compensation
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	(2)	(2)
Property and other
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	$ 6	$ (9)