Loss and Loss Adjustment Expense Reserves (Loss and LAE Activity) (Narrative) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Loss And Loss Adjustment Expense Reserves [Line Items]
Weighted average risk-free rate used to discount claim liability	3.97%
Percentage of commutation of outstanding insured bonds	27.00%
Lae [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Losses and loss adjustment	$ 6	$ 3	$ 47
Loss and loss adjustment expense reserves	$ 8	$ 12
Changes in Loss and LAE Reserves	one-year