Quarterly report pursuant to Section 13 or 15(d)

DERIVATIVE INSTRUMENTS (Narrative) (Details)

v3.8.0.1
DERIVATIVE INSTRUMENTS (Narrative) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Jan. 01, 2018
Dec. 31, 2017
Derivative [Line Items]        
Natural Gas Hedges $ 3.5     $ 3.5
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax (0.4)      
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net 0.1      
Derivative assets 93.6   $ 51.0 39.4
Derivative Liability 4.4     2.7
Not Designated as Hedging Instrument [Member]        
Derivative [Line Items]        
Derivative assets 93.6     39.4
Derivative Liability 4.2     2.4
Customer Supply Agreement [Member] | Not Designated as Hedging Instrument [Member] | Product Revenues [Member]        
Derivative [Line Items]        
Amount of gain/(loss) recognized in income on derivative 41.9 $ 17.8    
Customer Supply Agreement [Member] | Not Designated as Hedging Instrument [Member] | Derivative Financial Instruments, Assets [Member]        
Derivative [Line Items]        
Derivative assets 91.2     37.9
Provisional Pricing Arrangements [Member] | Not Designated as Hedging Instrument [Member] | Product Revenues [Member]        
Derivative [Line Items]        
Amount of gain/(loss) recognized in income on derivative 3.2 $ 15.7    
Provisional Pricing Arrangements [Member] | Not Designated as Hedging Instrument [Member] | Derivative Financial Instruments, Assets [Member]        
Derivative [Line Items]        
Derivative assets $ 2.4     $ 1.5