COMPREHENSIVE INCOME (LOSS) - SUMMARY OF COMPREHENSIVE INCOME, NET OF TAX (Details) - Foreign Currency Translation Gain (Loss) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Condensed Statement of Income Captions [Line Items]
Foreign currency translation gains	$ 0.0	$ 248.2	$ 0.0	$ 304.8
Foreign currency translation losses	(223.4)	0.0	(139.4)	0.0
Net Investment Hedging
Condensed Statement of Income Captions [Line Items]
Foreign currency translation gains	31.0	0.0	12.1	0.0
Foreign currency translation losses	$ 0.0	$ (24.2)	$ 0.0	$ (33.6)