Other Financial Data - Schedule of Allowance for Doubtful Accounts (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at beginning of period	$ 65	$ 61	$ 59	$ 56
Provision charged to Other general expenses	3	5	11	11
Accounts written off, net of recoveries	(6)	(7)	(8)	(10)
Foreign currency translation and other	0	0	0	2
Balance at end of period	$ 62	$ 59	$ 62	$ 59