Loss And Loss Adjustment Expense Reserves (Schedule Of Loss And Loss Adjustment Expenses Reserves) (Detail) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017
Loss And Loss Adjustment Expense Reserves [Line Items]
Changes in unearned premium revenue		$ 74	$ 97
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		(100)
Accretion of claim liability discount		12
Changes in discount rates		15
Changes in assumptions		112
Changes in unearned premium revenue		7
Changes in LAE		9
Other	[1]	1
Gross loss and LAE reserve, ending balance		$ 1,035

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