PENSION AND POST-RETIREMENT PLANS - COMPONENTS OF NET PERIODIC BENEFIT COST (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension Benefits
Components of Net Periodic Benefit Costs:
Service cost	$ 1.1	$ 1.0
Interest cost	2.2	2.4
Expected return on plan assets	(3.4)	(3.4)
Amortization of net loss	1.1	1.2
Amortization of prior service cost	(0.6)	(0.6)
Net periodic benefit cost	0.4	0.6
Post-retirement Benefits
Components of Net Periodic Benefit Costs:
Service cost	0.2	0.4
Interest cost	0.2	0.7
Amortization of net loss	0.4	0.3
Amortization of prior service cost	(0.9)
Net periodic benefit cost	$ (0.1)	$ 1.4