Claim and Claim Adjustment Expense Reserves (Commercial - Net Prior Year Claim and Allocated Claim Adjustment Expense Reserve Development) (Details) - Commercial - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Liability for Claims and Claims Adjustment Expense [Line Items]
Commercial	$ 107	$ 33	$ 49
General Liability	75	149	67
Workers' Compensation	(202)	(203)	(152)
Property and Other	4	(1)	(7)
Total pretax (favorable) unfavorable development	$ (16)	$ (22)	$ (43)