Loss And Loss Adjustment Expense Reserves (Schedule Of Loss And Loss Adjustment Expenses Reserves) (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Loss And Loss Adjustment Expense Reserves [Line Items]
Changes in unearned premium revenue		$ 43	$ 39
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Gross loss and LAE reserve, beginning balance		934
Loss payments for cases		(84)
Accretion of claim liability discount		5
Changes in discount rates		(27)
Changes in assumptions		(37)
Changes in unearned premium revenue		24
Changes in LAE		(9)
Other	[1]	0
Gross loss and LAE reserve, ending balance		$ 806

[1] Primarily changes in amount and timing of collections.