Revenues - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
Capitalized Contract Cost [Line Items]
Remaining performance obligation	$ 448,000,000
Remaining performance obligation, expected recognition period	3 years
Impairment losses	$ 0
Increase driven by payments received or due in advance of satisfying performance obligations	345,000,000	$ 334,000,000
Revenue recognized that was included in contract liability	65,000,000
Other long-term assets	80,000,000	$ 65,000,000	$ 77,000,000
Sales Commissions
Capitalized Contract Cost [Line Items]
Commissions amortization	2,000,000
Deferred commissions	12,000,000
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
Capitalized Contract Cost [Line Items]
Other long-term assets			12,000,000
Prepaid expenses and other current assets
Capitalized Contract Cost [Line Items]
Contract assets recorded in prepaids and other current assets	$ 6,000,000		$ 7,000,000