Revenues, Unbilled Revenue and Deferred Revenue (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Contracts with Customers, Assets and Liabilities [Abstract]
Unbilled revenue	$ 64.6	$ 0.0
Deferred revenue	219.1	$ 224.7
Other Current Assets [Member]
Contracts with Customers, Assets and Liabilities [Abstract]
Unbilled revenue (current amount)	64.4
Other Assets [Member]
Contracts with Customers, Assets and Liabilities [Abstract]
Unbilled revenue (noncurrent)	0.2
Other Current Liabilities [Member]
Contracts with Customers, Assets and Liabilities [Abstract]
Deferred revenue (current amount)	78.5
Other Liabilities [Member]
Contracts with Customers, Assets and Liabilities [Abstract]
Deferred revenue (noncurrent)	$ 140.6