Loss And Loss Adjustment Expense Reserves (Loss And LAE Activity) (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Loss And Loss Adjustment Expense Reserves [Line Items]
Weighted average risk-free rate used to discount claim liability			2.07%
Losses and loss adjustment	$ 140	$ 59	$ 102	$ 131
Gross potential recoveries					$ 108
Lae [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Losses and loss adjustment			10	$ 22
Loss and loss adjustment expense reserves	$ 47		$ 47		$ 60
Changes in Loss and LAE Reserves			one-year