Stockholders' Equity (Narrative) (Detail) - USD ($) shares in Millions	1 Months Ended	3 Months Ended
	Jan. 31, 2017	Mar. 31, 2017	Mar. 31, 2016
Stockholders Equity [Line Items]
Proceeds from Issuance of Preferred Stock, Preference Stock, and Warrants	$ 90
Document Period End Date		Mar. 31, 2017
Document Fiscal Year Focus		2017
Other Comprehensive Income Unrealized Gain Loss On Cash Flow Hedges Arising During Period Net Of Tax		$ 0	$ (4,000,000)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax		1,000,000	1,000,000
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax		1,000,000	$ (3,000,000)
Stock Repurchase Program, Authorized Amount		$ 1,500,000,000
Stock Repurchased During Period, Shares		1.5	3.0
Stock Repurchased During Period, Value		$ 50,000,000	$ 80,000,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount		250,000,000
Selling, General and Administrative Expenses [Member]
Stockholders Equity [Line Items]
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, before Tax		2,000,000	1,000,000
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Net of Tax		$ 1,000,000	$ 1,000,000