Loss And Loss Adjustment Expense Reserves (Schedule Of Loss And Loss Adjustment Expenses Reserves) (Detail) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015
Loss And Loss Adjustment Expense Reserves [Line Items]
Changes in unearned premium revenue		$ 197	$ 274
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Gross loss and LAE reserve, beginning balance		516
Loss payments for cases with reserves		(113)
Accretion of claim liability discount		6
Changes in discount rates		31
Changes in assumptions		13
Changes in unearned premium revenue		(8)
Changes in LAE		8
Other	[1]	60
Gross loss and LAE reserve, ending balance		$ 513

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