Revenues, Significant Changes in Unbilled Revenue (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Significant Changes in Unbilled Revenue [Roll Forward]
Balance at beginning of period (upon adoption of ASC 606)	$ 0.0
Unbilled revenue included in opening balance transferred to other accounts during period	0.0	[1]
Unbilled revenue recorded during period	321.7
Unbilled revenue recorded during period transferred to other accounts	(310.6)	[1]
Unbilled revenue recorded in connection with business combination	2.2
Other changes	0.0
Balance at end of period	$ 13.3

[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.