Loss and Loss Adjustment Expense Reserves (Loss and LAE Activity) (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Loss And Loss Adjustment Expense Reserves [Line Items]
Weighted average risk-free rates used to discount claim liability	4.33%		3.97%
Lae [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Losses and loss adjustment	$ 2	$ 2
Loss and loss adjustment expense reserves	$ 8		$ 8
Changes in Loss and LAE Reserves	one-year