Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Cash, Cash Equivalents and Restricted Cash
Cash and cash equivalents	$ 477	$ 448	$ 458	$ 597
Current restricted cash	8	10	6	9
Restricted cash non current	1	1	1	1
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Total	486	459	$ 465	$ 607
Other Non-cash items
Noncash capital expenditures	97	$ 124
Payment of indemnification guarantees	$ 45