Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Cash, Cash Equivalents and Restricted Cash
Cash and cash equivalents	$ 549	$ 448	$ 433	$ 597
Current restricted cash	8	10	7	9
Restricted cash non current		1	1	1
Total cash, cash equivalents and restricted cash	557	459	$ 441	$ 607
Other Non-cash items
PP&E acquired but not yet paid	97	$ 124
Payment of indemnification guarantees	$ 45