Revenues, Significant Changes in Deferred Revenue (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018 USD ($)
Significant Changes in Deferred Revenue [Roll Forward]
Balance at beginning of period (upon adoption of ASC 606)	$ 224.7
Deferred revenue included in opening balance transferred to other accounts during period	(72.8)	[1]
Deferred revenue recorded during period	201.1
Deferred revenue recorded during period transferred to other accounts	(110.8)	[1]
Deferred revenue recorded in connection with business combination	0.0
Balance at end of period	$ 242.2

[1] Unbilled revenues are transferred to accounts receivable once we have an unconditional right to consideration from the customer. Deferred revenues are recognized as revenue upon satisfaction of our performance obligation to the customer.