DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES - Location and Fair Value Amounts of Derivative Instruments Reported in Balance Sheet (Details) $ in Millions	Jun. 30, 2017 USD ($)
Asset Derivatives
Derivative contracts	$ 11.4
Liability Derivatives
Derivative contracts, liabilities	0.3
Not Designated as Hedging Instrument | Commodity contracts
Asset Derivatives
Derivative contracts	11.4
Liability Derivatives
Derivative contracts, liabilities	0.3
Not Designated as Hedging Instrument | Commodity contracts | Current assets: Fair value of derivative contracts
Asset Derivatives
Derivative contracts	8.0
Not Designated as Hedging Instrument | Commodity contracts | Long-term assets: Fair value of derivative contracts
Asset Derivatives
Derivative contracts	3.4
Not Designated as Hedging Instrument | Commodity contracts | Current liabilities: Fair value of derivative contracts
Liability Derivatives
Derivative contracts, liabilities	0.3
Not Designated as Hedging Instrument | Commodity contracts | Long-term liabilities: Fair value of derivative contracts
Liability Derivatives
Derivative contracts, liabilities	$ 0.0