Other Financial Data - Schedule of Allowance for Doubtful Accounts (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 64	$ 65	$ 64	$ 59
Provision charged to Other general expenses	4	3	12	11
Accounts written off, net of recoveries	(3)	(6)	(11)	(8)
Balance at end of period	$ 65	$ 62	$ 65	$ 62