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, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Liability for Claims and Claims Adjustment Expense [Line Items]
Commercial	$ 25	$ 0	$ 46	$ 11
General Liability	28	0	47	70
Workers' Compensation	(57)	(2)	(106)	(100)
Property and Other	1	0	2	2
Total pretax (favorable) unfavorable development	$ (3)	$ (2)	$ (11)	$ (17)