Quarterly report pursuant to Section 13 or 15(d)

DERIVATIVE INSTRUMENTS - Schedule Of Derivative Instruments In Statement Of Financial Position, Fair Value (Details)

v3.20.2
DERIVATIVE INSTRUMENTS - Schedule Of Derivative Instruments In Statement Of Financial Position, Fair Value (Details) - USD ($)
$ in Millions
Sep. 30, 2020
Dec. 31, 2019
Customer Supply Agreement [Member] | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset $ 34.5 $ 44.5
Provisional Pricing Arrangements [Member] | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset 26.9 1.3
Provisional Pricing Arrangements [Member] | Other Current Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Liability (0.3) (1.1)
Commodity Contract [Member] | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset 15.8  
Commodity Contract [Member] | Other Noncurrent Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset 1.8  
Commodity Contract [Member] | Other Current Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Liability (8.7) (3.2)
Foreign Exchange Contract [Member] | Other Current Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Liability (0.6)  
Foreign Exchange Contract [Member] | Other Noncurrent Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Liability (0.1)  
Designated as Hedging Instrument [Member] | Customer Supply Agreement [Member] | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset 0.0 0.0
Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member] | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset 0.0 0.0
Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member] | Other Current Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Liability 0.0 0.0
Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset 7.9 0.0
Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Noncurrent Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset 1.8 0.0
Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Current Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Liability (1.8) (3.2)
Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other Current Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Liability (0.6) 0.0
Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other Noncurrent Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Liability (0.1) 0.0
Not Designated as Hedging Instrument [Member] | Customer Supply Agreement [Member] | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset 34.5 44.5
Not Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member] | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset 26.9 1.3
Not Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member] | Other Current Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Liability (0.3) (1.1)
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset 7.9 0.0
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Noncurrent Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset 0.0 0.0
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Current Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Liability (6.9) 0.0
Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other Current Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Liability 0.0 0.0
Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other Noncurrent Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Liability $ 0.0 $ 0.0