Quarterly report pursuant to Section 13 or 15(d)

FAIR VALUE MEASUREMENTS - Fair Value of Assets and Liabilities (Details)

v3.20.2
FAIR VALUE MEASUREMENTS - Fair Value of Assets and Liabilities (Details) - USD ($)
$ in Millions
Sep. 30, 2020
Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets, Fair Value Disclosure $ 79.0 $ 233.4
Liabilities, Fair Value Disclosure (9.7) (4.3)
Fair Value, Inputs, Level 1 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets, Fair Value Disclosure 0.0 0.0
Liabilities, Fair Value Disclosure 0.0 0.0
Fair Value, Inputs, Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets, Fair Value Disclosure 17.6 187.6
Liabilities, Fair Value Disclosure (9.4) (3.2)
Fair Value, Inputs, Level 3 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets, Fair Value Disclosure 61.4 45.8
Liabilities, Fair Value Disclosure (0.3) (1.1)
Cash and Cash Equivalents [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Cash equivalents   187.6
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Cash equivalents   0.0
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Cash equivalents   187.6
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Cash equivalents   0.0
Commodity Contract [Member] | Other Current Assets [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Asset 15.8  
Commodity Contract [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 1 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Asset 0.0  
Commodity Contract [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Asset 15.8  
Commodity Contract [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Asset 0.0  
Commodity Contract [Member] | Other Noncurrent Assets [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Asset 1.8  
Commodity Contract [Member] | Other Noncurrent Assets [Member] | Fair Value, Inputs, Level 1 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Asset 0.0  
Commodity Contract [Member] | Other Noncurrent Assets [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Asset 1.8  
Commodity Contract [Member] | Other Noncurrent Assets [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Asset 0.0  
Commodity Contract [Member] | Other Current Liabilities [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability (8.7) (3.2)
Commodity Contract [Member] | Other Current Liabilities [Member] | Fair Value, Inputs, Level 1 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 0.0 0.0
Commodity Contract [Member] | Other Current Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability (8.7) (3.2)
Commodity Contract [Member] | Other Current Liabilities [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 0.0 0.0
Customer Supply Agreement [Member] | Other Current Assets [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Asset 34.5 44.5
Customer Supply Agreement [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 1 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Asset 0.0 0.0
Customer Supply Agreement [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Asset 0.0 0.0
Customer Supply Agreement [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Asset 34.5 44.5
Provisional Pricing Arrangements [Member] | Other Current Assets [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Asset 26.9 1.3
Provisional Pricing Arrangements [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 1 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Asset 0.0 0.0
Provisional Pricing Arrangements [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Asset 0.0 0.0
Provisional Pricing Arrangements [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Asset 26.9 1.3
Provisional Pricing Arrangements [Member] | Other Current Liabilities [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability (0.3) (1.1)
Provisional Pricing Arrangements [Member] | Other Current Liabilities [Member] | Fair Value, Inputs, Level 1 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 0.0 0.0
Provisional Pricing Arrangements [Member] | Other Current Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 0.0 0.0
Provisional Pricing Arrangements [Member] | Other Current Liabilities [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability (0.3) $ (1.1)
Foreign Exchange Contract [Member] | Other Current Liabilities [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability (0.6)  
Foreign Exchange Contract [Member] | Other Current Liabilities [Member] | Fair Value, Inputs, Level 1 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 0.0  
Foreign Exchange Contract [Member] | Other Current Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability (0.6)  
Foreign Exchange Contract [Member] | Other Current Liabilities [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 0.0  
Foreign Exchange Contract [Member] | Other Noncurrent Liabilities [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability (0.1)  
Foreign Exchange Contract [Member] | Other Noncurrent Liabilities [Member] | Fair Value, Inputs, Level 1 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 0.0  
Foreign Exchange Contract [Member] | Other Noncurrent Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability (0.1)  
Foreign Exchange Contract [Member] | Other Noncurrent Liabilities [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability $ 0.0