ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	$ 699.5	$ 682.4	$ 678.2	$ 499.2	$ 489.4	$ 494.9	$ 678.2	$ 494.9
Net gain in prior service cost				0.7				0.8
Amortization of prior service cost	(1.1)			(2.2)			(3.5)	(2.9)
Amortization of net loss	1.1			1.0			2.9	3.1
Other adjustments	0.1							0.2
Balance at the end of the period	743.7	699.5	682.4	518.6	499.2	489.4	743.7	518.6
Pensions
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	(48.9)	(49.3)	(40.6)	(40.5)	(41.0)	(41.4)	(40.6)	(41.4)
Reclassification adjustment related to the Tax Act			(9.2)
Amortization of prior service cost	(0.4)	(0.5)	(0.4)	(0.4)	(0.3)	(0.4)
Amortization of net loss	0.9	0.9	0.9	0.8	0.8	0.8
Balance at the end of the period	(48.4)	(48.9)	(49.3)	(40.1)	(40.5)	(41.0)	(48.4)	(40.1)
Post Retirement
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	18.1	18.4	15.6	18.5	18.2	18.1	15.6	18.1
Reclassification adjustment related to the Tax Act			3.4
Net gain in prior service cost				0.7
Amortization of prior service cost	(0.7)	(0.5)	(0.9)	(1.7)
Amortization of net loss	0.3	0.2	0.3	0.2	0.3	0.1
Balance at the end of the period	17.7	18.1	18.4	17.7	18.5	18.2	17.7	17.7
Non-Qualified Plans
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	(0.4)	(0.4)	(0.3)	(0.3)	(0.4)	(0.4)	(0.3)	(0.4)
Reclassification adjustment related to the Tax Act			(0.2)
Amortization of prior service cost		(0.1)		(0.1)
Amortization of net loss	(0.1)	0.1	0.1		0.1
Balance at the end of the period	(0.5)	(0.4)	(0.4)	(0.4)	(0.3)	(0.4)	(0.5)	(0.4)
Other
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	(0.4)	0.6	0.4	0.4	0.3	0.1	0.4	0.1
Net gain in prior service cost					0.1
Amortization of net loss		(0.7)
Other adjustments	0.1	(0.3)	0.2			0.2
Balance at the end of the period	(0.3)	(0.4)	0.6	0.4	0.4	0.3	(0.3)	0.4
Accumulated Other Comprehensive Income (Loss)
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	(31.6)	(30.7)	(24.9)	(21.9)	(22.9)	(23.6)	(24.9)	(23.6)
Reclassification adjustment related to the Tax Act			(6.0)
Net gain in prior service cost				0.7	0.1
Amortization of prior service cost	(1.1)	(1.1)	(1.3)	(2.2)	(0.3)	(0.4)
Amortization of net loss	1.1	0.5	1.3	1.0	1.2	0.9
Other adjustments	0.1	(0.3)	0.2			0.2
Balance at the end of the period	$ (31.5)	$ (31.6)	$ (30.7)	$ (22.4)	$ (21.9)	$ (22.9)	$ (31.5)	$ (22.4)