Stockholders' Equity (Narrative) (Detail) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Stockholders Equity [Line Items]
Other Comprehensive Income Unrealized Gain Loss On Cash Flow Hedges Arising During Period Net Of Tax			$ (10)	$ 0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	$ 2	$ 2	4	4
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	1	2	2	(3)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax			(8)	$ (3)
Stock Repurchase Program, Authorized Amount	1,200		$ 1,200
Stock Repurchased During Period, Shares			6.5	2.2
Stock Repurchased During Period, Value			$ 180	$ 116
Stock Repurchase Program, Remaining Authorized Repurchase Amount	260		260
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, before Tax	2	1	3	2
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Net of Tax	$ 1	$ 0	$ 2	$ 1