Loss And Loss Adjustment Expense Reserves (Loss And LAE Activity) (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Loss And Loss Adjustment Expense Reserves [Line Items]
Weighted average risk-free rate used to discount claim liability			1.78%
Gross potential recoveries					$ 108
Lae [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Losses and loss adjustment	$ 16	$ 6	$ 26	$ 28
Loss and loss adjustment expense reserves	$ 37		$ 37		$ 60
Changes in Loss and LAE Reserves			one-year