Stockholders' Equity (Narrative) (Detail) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Stockholders Equity [Line Items]
Document Period End Date			Sep. 30, 2016
Other Comprehensive Income Unrealized Gain Loss On Cash Flow Hedges Arising During Period Net Of Tax			$ (7)	$ (8)
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	3	4
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax			(4)	$ (4)
Stock Repurchase Program, Authorized Amount	$ 1,200		$ 1,200
Stock Repurchased During Period, Shares			9.5	5.9
Stock Repurchased During Period, Value			$ 290	$ 277
Stock Repurchase Program, Remaining Authorized Repurchase Amount	150		150
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, before Tax	1	3	4	5
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Net of Tax	$ 1	$ 2	$ 3	$ 3