REVENUES - Contract Liability (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Change in contract liability
Contract liability as of beginning of period	$ 75.8	$ 79.0
Revenue recognized: Amounts included in the contract liability at the beginning of the period	(75.8)	(79.0)
Increases due to invoices issued, excluding amounts recognized as revenues during the period	80.2	87.1
Business combination	3.0	0.2
Contract liability as of end of period	$ 83.2	$ 87.3