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, 2023	Dec. 31, 2022	Dec. 31, 2021
Liability for Claims and Claims Adjustment Expense [Line Items]
Commercial	$ 33	$ 49	$ 53
General Liability	149	67	15
Workers' Compensation	(203)	(152)	(82)
Property and Other	(1)	(7)	8
Total pretax (favorable) unfavorable development	$ (22)	$ (43)	$ (6)