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, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Liability for Claims and Claims Adjustment Expense [Line Items]
Commercial	$ 21	$ 11	$ 21	$ 11
General Liability	19	70	19	70
Workers' Compensation	(47)	(96)	(49)	(98)
Property and Other	1	2	1	2
Total pretax (favorable) unfavorable development	$ (6)	$ (13)	$ (8)	$ (15)