Other Financial Data - Schedule of Allowance for Doubtful Accounts (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at beginning of period	$ 59	$ 56
Provision charged to Other general expenses	8	6
Accounts written off, net of recoveries	(3)	(3)
Foreign currency translation	1	2
Balance at end of period	$ 65	$ 61