PENSION AND POST-RETIREMENT PLANS - COMPONENTS OF NET PERIODIC BENEFIT COST (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pension Benefits
Components of Net Periodic Benefit Cost (Benefit):
Service cost	$ 1.1	$ 0.9	$ 2.2	$ 1.9
Interest cost	2.1	2.4	4.3	4.8
Expected return on plan assets	(3.4)	(3.4)	(6.8)	(6.8)
Amortization of net loss	1.3	1.3	2.4	2.5
Amortization of prior service credit	(0.6)	(0.5)	(1.2)	(1.1)
Net periodic benefit cost	0.5	0.7	0.9	1.3
Post-retirement Benefits
Components of Net Periodic Benefit Cost (Benefit):
Service cost	0.1	0.4	0.3	0.8
Interest cost	0.3	0.7	0.5	1.4
Amortization of net loss	0.4	0.3	0.8	0.6
Amortization of prior service credit	(0.9)		(1.8)
Net periodic benefit cost	$ (0.1)	$ 1.4	$ (0.2)	$ 2.8