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, 2024	Dec. 31, 2023	Dec. 31, 2022
Property and casualty
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	$ 48	$ 48	$ (32)
Medical professional liability
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	(8)	5	18
Other professional liability and management liability
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	49	37	50
Surety
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	(68)	(43)	(83)
Warranty
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	20	(11)	(21)
Commercial auto
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	107	33	49
General liability
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	75	149	67
Workers’ compensation
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	(202)	(203)	(152)
Other property and casualty operations
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	(4)	10	(24)
Other insurance operations
Net Prior Year Development [Abstract]
Total pretax (favorable) unfavorable development	$ 79	$ 71	$ 64