ACCUMULATED OTHER COMPREHENSIVE LOSS - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		$ (1,221.2)	$ (1,056.8)
Foreign currency translation adjustment, net of tax		(5.2)
Amortization of pension related costs, net of tax	[1],[2]	2.5	2.2
Other comprehensive (loss) gain	[3]	(2.7)	0.9
Ending balance		(1,435.8)	(1,132.2)
Amortization of pension related costs, tax benefit (expense)		(0.3)	(0.3)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(247.4)	(234.2)
Other comprehensive (loss) gain	[3]	(2.7)	0.9
Ending balance		(250.1)	$ (233.3)
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(27.3)
Foreign currency translation adjustment, net of tax		(5.2)
Other comprehensive (loss) gain		(5.2)
Ending balance		(32.5)
Actuarial (Loss) Gain on Post-retirement Benefits
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(219.8)
Amortization of pension related costs, net of tax		2.5
Other comprehensive (loss) gain		2.5
Ending balance		(217.3)
Amortization of pension related costs, tax benefit (expense)		(0.3)
Other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(0.3)
Other comprehensive (loss) gain		0.0
Ending balance		$ (0.3)

[1] Net of tax expense of $0.3 million for each of the three months ended March 31, 2020 and 2019.

[2] This amount is included in the computation of net periodic benefit costs (income). See Note 10, "Pension and Post-Retirement Benefits," for additional information regarding net periodic benefit costs (income).

[3] See Note 13, "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, 2020 and 2019, respectively.