Loss And Loss Adjustment Expense Reserves (Schedule Of Loss And Loss Adjustment Expenses Reserves) (Detail) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017
Loss And Loss Adjustment Expense Reserves [Line Items]
Changes in unearned premium revenue		$ 142	$ 149
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Gross loss and LAE reserve, beginning balance		979
Loss payments for cases		(344)
Accretion of claim liability discount		18
Changes in discount rates		25
Changes in assumptions		336
Changes in unearned premium revenue		12
Changes in LAE		8
Other	[1]	(1)
Gross loss and LAE reserve, ending balance		$ 1,033

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