Claim and Claim Adjustment Expense Reserves (Commercial - Net Prior Year Claim and Allocated Claim Adjustment Expense Reserve Development) (Details) - Commercial - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Liability for Claims and Claims Adjustment Expense [Line Items]
Commercial Auto	$ 0	$ 0	$ 0	$ 50
General Liability	56	62	111	62
Workers' Compensation	(32)	(66)	(32)	(65)
Property and Other	(29)	0	(29)	0
Total pretax (favorable) unfavorable development	$ (5)	$ (4)	$ 50	$ 47