ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	$ 677.2	$ 494.9	$ 450.6
Net gain in prior service cost		0.8	24.1
Amortization of prior service cost	(4.7)	(4.0)	(2.2)
Amortization of net loss (gain)	1.1	1.7	1.2
Other adjustments		0.2	0.2
Balance at the end of the period	755.3	677.2	494.9
Comprehensive Income (Loss):
Tax benefit (expense) on other comprehensive income (loss)	0.2	(4.4)	(14.2)
Pensions
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	(40.6)	(41.4)
Reclassification adjustment related to the Tax Act	(9.2)
Amortization of prior service cost	(1.7)	(1.4)
Amortization of net loss (gain)	(4.3)	2.2
Balance at the end of the period	(55.8)	(40.6)	(41.4)
Post Retirement
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	15.6	18.1
Net gain in prior service cost		0.7
Reclassification adjustment related to the Tax Act	3.4
Amortization of prior service cost	(2.9)	(2.5)
Amortization of net loss (gain)	5.6	(0.7)
Balance at the end of the period	21.7	15.6	18.1
Non-Qualified Plans
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	(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 (gain)	0.5	0.2
Balance at the end of the period	(0.1)	(0.3)	(0.4)
Other
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	0.4	0.1
Net gain in prior service cost		0.1
Amortization of net loss (gain)	(0.7)
Other adjustments		0.2
Balance at the end of the period	(0.3)	0.4	0.1
Accumulated Other Comprehensive Income (Loss)
Changes in accumulated other comprehensive loss by component, net of taxes
Balance at the beginning of the period	(24.9)	(23.6)	(46.9)
Net gain in prior service cost		0.8
Reclassification adjustment related to the Tax Act	(6.0)
Amortization of prior service cost	(4.7)	(4.0)
Amortization of net loss (gain)	1.1	1.7
Other adjustments		0.2
Balance at the end of the period	$ (34.5)	$ (24.9)	$ (23.6)