Revenues, Unbilled Revenue and Deferred Revenue (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Contracts with Customers, Assets and Liabilities [Abstract]
Unbilled revenue	$ 73.7	$ 13.3
Deferred revenue	301.1	$ 291.2
Other Current Assets [Member]
Contracts with Customers, Assets and Liabilities [Abstract]
Unbilled revenue (current amount)	73.7
Other Current Liabilities [Member]
Contracts with Customers, Assets and Liabilities [Abstract]
Deferred revenue (current amount)	83.0
Other Liabilities [Member]
Contracts with Customers, Assets and Liabilities [Abstract]
Deferred revenue (noncurrent)	$ 218.1

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