Stockholders' Equity (Narrative) (Detail) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Stockholders Equity [Line Items]
Other Comprehensive Income Unrealized Gain Loss On Cash Flow Hedges Arising During Period Net Of Tax	$ (4)	$ (4)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	2
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	1	1
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	(3)	$ (3)
Stock Repurchase Program, Authorized Amount	$ 1,200
Stock Repurchased During Period, Shares	3.0	0.5
Stock Repurchased During Period, Value	$ 80	$ 31
Stock Repurchase Program, Remaining Authorized Repurchase Amount	360
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, before Tax	1
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Net of Tax	$ 1