Loss And Loss Adjustment Expense Reserves (Schedule Of Loss And Loss Adjustment Expenses Reserves) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Loss And Loss Adjustment Expense Reserves [Line Items]
Changes in unearned premium revenue		$ 263	$ 371	$ 412
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Gross loss and LAE reserve, beginning balance		516	506
Loss payments for cases with reserves		(128)	(200)
Accretion of claim liability discount		8	8
Changes in discount rates		5	(41)
Changes in assumptions		78	88
Changes in unearned premium revenue		(15)	14
Changes in LAE		14	4
Other	[1]	63	137
Gross loss and LAE reserve, ending balance		$ 541	$ 516	$ 506

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