Claim and Claim Adjustment Expense Reserves - Net Prior Year Loss Reserve Development in Property and Casualty Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Property and casualty
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	$ 48	$ (32)	$ 11
Medical professional liability
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	5	18	23
Other professional liability and management liability
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	37	50	24
Surety
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	(43)	(83)	(73)
Warranty
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	(11)	(21)	(14)
Commercial auto
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	33	49	53
General liability
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	149	67	15
Workers’ compensation
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	(203)	(152)	(82)
Other property and casualty operations
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	10	(24)	5
Other insurance operations
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	$ 71	$ 64	$ 60