Debt (Summary Of Interest Expense) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Disclosure Debt Summary Of Interest Expense [Abstract]
Cash payments for interest	$ (4)	$ (64)	$ (65)	$ (106)
Non-cash interest	1	1	4	4
Net changes in accruals	34	(10)	10	(1)
Total interest expense	$ 39	$ 55	$ 79	$ 109