ACCUMULATED OTHER COMPREHENSIVE LOSS - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		$ (1,056.8)	$ (770.4)
Other comprehensive income	[1]	0.9	0.2
Ending balance		(1,132.2)	(855.7)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(234.2)	(228.4)
Other comprehensive income	[1]	0.9	0.2
Ending balance		(233.3)	$ (228.2)
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(24.4)
Other comprehensive income		(1.3)
Ending balance		(25.7)
Actuarial (Loss) Gain on Post-retirement Benefits
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(209.5)
Other comprehensive income		2.2
Ending balance		(207.3)
Actuarial (Loss) Gain on Post-retirement Benefits - Amortization of pension related costs
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Other comprehensive income		2.2
Other comprehensive income (loss), tax expense (benefit)		(0.3)
Other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(0.3)
Other comprehensive income		0.0
Ending balance		$ (0.3)

[1] See Note 14, "Accumulated Other Comprehensive Loss," regarding the changes in the accumulated balances for each component of other comprehensive loss during the three months ended March 31, 2019.