BENEFIT PLANS - OTHER CHANGES IN PLAN ASSETS AND BENEFIT OBLIGATIONS RECOGNIZED IN AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss (gain)	$ 13.3	$ 20.3	$ (48.6)
Net prior service cost (credit)	0.3	0.4	(0.3)
Amortization	(6.7)	(4.9)	(7.6)
Total recognized in AOCI	6.9	15.8	(56.5)
Total recognized in net periodic benefit cost and AOCI	31.8	40.5	(30.7)
Other Postemployment Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss (gain)	(0.2)	1.4	(0.4)
Net prior service cost (credit)	0.0	0.0	0.0
Amortization	(0.1)	(0.2)	(0.2)
Total recognized in AOCI	(0.3)	1.2	(0.6)
Total recognized in net periodic benefit cost and AOCI	$ 0.8	$ 2.3	$ 0.6