STOCKHOLDERS' DEFICIT - Share-Based Compensation Cost (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Tax benefit related to share-based compensation expense	$ 4.2	$ 5.0	$ 4.2
Unrecognized compensation cost related to arrangements that will vest based on service conditions	$ 17.5
Weighted average period for recognition	3 years
Unrecognized compensation cost related to arrangements that will vest based on market, performance and service conditions	$ 26.5
Corporate expenses
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Share-based compensation payments recorded in corporate expenses	$ 12.1	$ 13.1	$ 11.1