Stockholders' Equity (Schedule of Components of Other Comprehensive Income (Loss), Net) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Comprehensive Income (Loss) [Line Items]
Unrealized gain (loss) on marketable securities, gross amount	$ 0	$ 0	$ 0
Unrealized gain (loss) on marketable securities, income tax (provision) benefit	(1)	0	0
Unrealized gain (loss) on marketable securities, net amount	(1)	0	0
Foreign currency translation, gross amount	162	(22)	(193)
Foreign currency translation, income tax (provision) benefit	12	11	5
Foreign currency translation, net amount	174	(11)	(188)
Gain (loss) on cash flow hedges, gross amount	0	5	3
Gain (loss) on cash flow hedges, income tax (provision) benefit	(1)	0	(1)
Gain (loss) on cash flow hedges, net amount	(1)	5	2
Pension and postretirement benefits, gross amount	7	(5)	4
Pension and postretirement benefits, income tax (provision) benefit	2	1	(1)
Pension and postretirement benefits, net amount	9	(4)	3
Total other comprehensive income (loss), gross amount	169	(22)	(186)
Total other comprehensive income (loss), income tax (provision) benefit	12	12	3
Total other comprehensive income (loss), net of tax	$ 181	$ (10)	$ (183)