ACCUMULATED OTHER COMPREHENSIVE LOSS - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
		Dec. 31, 2019		Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance				$ (1,056.8)	$ (770.4)
Foreign currency translation adjustment, net of tax				(2.9)	(9.4)
Amortization of pension related costs, net of tax(b)(c)	[1],[2]			9.0	8.4
Pension re-measurement					(5.5)
Amortization of deferred losses, net of tax					0.7
Other comprehensive (loss) income		$ (13.2)	[3]	(13.2)	(5.8)	[3]
Ending balance		(1,221.2)		(1,221.2)	(1,056.8)
Amortization of pension related costs, tax benefit (expense)				1.1	1.0
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance				(234.2)	(228.4)
Other comprehensive (loss) income	[3]	(13.2)			(5.8)
Ending balance		(247.4)		(247.4)	(234.2)
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance				(24.4)	(15.0)
Foreign currency translation adjustment, net of tax				(2.9)	(9.4)
Other comprehensive (loss) income				(2.9)	(9.4)
Ending balance		(27.3)		(27.3)	(24.4)
Foreign currency translation adjustment, tax benefit (expense)				1.8	(0.1)
Actuarial (Loss) Gain on Post-retirement Benefits
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance				(209.5)	(212.4)
Amortization of pension related costs, net of tax(b)(c)				9.0	8.4
Pension re-measurement				(19.3)	(5.5)
Other comprehensive (loss) income				(10.3)	2.9
Ending balance		(219.8)		(219.8)	(209.5)
Amortization of pension related costs, tax benefit (expense)				(1.1)	(1.0)
Pension re-measurement, tax benefit (expense)				5.2	2.5
Deferred Gain (Loss) - Hedging
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance				0.0	(0.7)
Amortization of deferred losses, net of tax					0.7
Other comprehensive (loss) income				0.0	0.7
Ending balance		0.0		0.0	0.0
Amortization of deferred losses, tax benefit (expense)					0.5
Other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance				(0.3)	(0.3)
Other comprehensive (loss) income				0.0	0.0
Ending balance		$ (0.3)		(0.3)	(0.3)
Deferred gain - hedging | Interest rate swap
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance				0.0	(0.7)
Ending balance					$ 0.0
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Pension re-measurement				$ (19.3)

[1] Net of tax expense of $1.1 million and $1.0 million for 2019 and 2018, respectively.

[2] This amount is included in the computation of net periodic benefit costs (income). See Note 12, "Pension and Post-Retirement Benefits," for additional information regarding net periodic benefit costs (income).

[3] See Note 15, "Accumulated Other Comprehensive Loss," regarding the changes in the accumulated balances for each component of other comprehensive loss during 2019 and 2018, respectively.