REVENUES - Contract Liability (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Change in contract liability
Contract liability	$ 81.9	$ 84.7	$ 79.0	$ 68.6
Revenue recognized: Amounts included in the contract liability at the beginning of the period	(79.0)	(68.6)
Revenue, Remaining Performance Obligation	81.9		$ 79.0
Increases due to invoices issued, excluding amounts recognized as revenues during the period	81.7	82.5
Business combination	$ 0.2	$ 2.2