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, 2025	Dec. 31, 2024	Dec. 31, 2023
Net Prior Year Development [Abstract]
Total pretax unfavorable development	$ 185	$ 48	$ 48
Property and casualty
Net Prior Year Development [Abstract]
Total pretax unfavorable development	51	(31)	(23)
Medical professional liability
Net Prior Year Development [Abstract]
Total pretax unfavorable development		(8)	5
Other professional liability and management liability
Net Prior Year Development [Abstract]
Total pretax unfavorable development	69	49	37
Surety
Net Prior Year Development [Abstract]
Total pretax unfavorable development	(50)	(68)	(43)
Warranty
Net Prior Year Development [Abstract]
Total pretax unfavorable development	10	20	(11)
Commercial auto
Net Prior Year Development [Abstract]
Total pretax unfavorable development	74	107	33
General liability
Net Prior Year Development [Abstract]
Total pretax unfavorable development	114	75	149
Workers’ compensation
Net Prior Year Development [Abstract]
Total pretax unfavorable development	(135)	(202)	(203)
Other property and casualty operations
Net Prior Year Development [Abstract]
Total pretax unfavorable development	(31)	(4)	10
Other insurance operations
Net Prior Year Development [Abstract]
Total pretax unfavorable development	$ 134	$ 79	$ 71