Revenues, Unbilled Revenue and Deferred Revenue (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Contracts with Customers, Assets and Liabilities [Abstract]
Unbilled revenue	$ 126.9	$ 0.0
Deferred revenue	242.2	$ 224.7
Other Current Assets [Member]
Contracts with Customers, Assets and Liabilities [Abstract]
Unbilled revenue (current amount)	126.9
Other Assets [Member]
Contracts with Customers, Assets and Liabilities [Abstract]
Unbilled revenue (noncurrent)	0.0
Other Current Liabilities [Member]
Contracts with Customers, Assets and Liabilities [Abstract]
Deferred revenue (current amount)	83.8
Other Liabilities [Member]
Contracts with Customers, Assets and Liabilities [Abstract]
Deferred revenue (noncurrent)	$ 158.4