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		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Liability for Claims and Claims Adjustment Expense [Line Items]
Commercial	$ 0	$ 25	$ 50	$ 46
General Liability	0	28	62	47
Workers' Compensation	(1)	(57)	(66)	(106)
Property and Other	0	1	0	2
Total pretax (favorable) unfavorable development	$ (1)	$ (3)	$ 46	$ (11)