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
	Mar. 31, 2024	Mar. 31, 2023
Liability for Claims and Claims Adjustment Expense [Line Items]
Commercial	$ 0	$ 0
General Liability	0	0
Workers' Compensation	(2)	(2)
Property and Other	0	0
Total pretax (favorable) unfavorable development	$ (2)	$ (2)