Annual report pursuant to Section 13 and 15(d)

DISCONTINUED OPERATIONS (Narrative) (Details)

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DISCONTINUED OPERATIONS (Narrative) (Details) - USD ($)
 3 Months Ended 12 Months Ended
Mar. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
Impairment of long-lived assets   $ 0 $ 0 $ 76,600,000
Discontinued Operation, Tax Effect of Discontinued Operation   0 0 (6,000,000)
Deconsolidation, Gain (Loss), Amount       (528,200,000)
Short-term loan receivable   7,700,000    
LOSS FROM DISCONTINUED OPERATIONS, net of tax   (18,700,000) (19,900,000) (892,100,000)
Potential Earn Out from North American Coal sale   50,000,000    
Contingent claims   55,600,000 0  
Canadian Entities [Member]        
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
Impairment of long-lived assets       0
Disposal Group, Including Discontinued Operation, Revenue   0 0 11,300,000
Discontinued Operation, Tax Effect of Discontinued Operation   0 0 5,800,000
Deconsolidation, Gain (Loss), Amount   (21,300,000) (17,500,000) (710,900,000)
Cost Method Investments   0 0  
Disposal Group, Including Discontinued Operation, Costs of Goods Sold   0 0 (11,100,000)
Disposal Group, Including Discontinued Operation, Gross Profit (Loss)   0 0 200,000
Disposal Group, Including Discontinued Operation, Operating Expense   0 0 33,800,000
Disposal Group, Including Discontinued Operation, Other Expense   0 0 (1,000,000)
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax   0 0 (34,600,000)
LOSS FROM DISCONTINUED OPERATIONS, net of tax   (21,300,000) (17,500,000) (739,700,000)
Loans to and Accounts Receivables from Bloom Lake Group, Fair Value Disclosure   51,600,000 48,600,000  
Discontinued Operations [Member]        
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
Impairment of long-lived assets       73,400,000
North American Coal [Member]        
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
Impairment of long-lived assets       73,400,000
Amounts released from escrow   10,300,000    
Disposal Group, Including Discontinued Operation, Revenue   0 0 392,900,000
Discontinued Operation, Tax Effect of Discontinued Operation   0 0 200,000
Tangible Asset Impairment Charges $ 73,400,000      
Disposal Group, Including Discontinued Operation, Costs of Goods Sold   0 0 (449,200,000)
Disposal Group, Including Discontinued Operation, Gross Profit (Loss)   0 0 (56,300,000)
Disposal Group, Including Discontinued Operation, Operating Expense   (500,000) 4,500,000 30,400,000
Disposal Group, Including Discontinued Operation, Other Expense   0 0 (1,800,000)
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax   2,600,000 (2,400,000) (79,200,000)
LOSS FROM DISCONTINUED OPERATIONS, net of tax   2,600,000 (2,400,000) (152,400,000)
Bloom Lake Group [Member]        
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
Deconsolidation, Gain (Loss), Amount $ 818,700,000      
Contingent Liabilities recognized in Consolidated Financials     37,200,000  
Contingent Liabilities of Deconsolidated Entities   (24,300,000) 0 $ (203,100,000)
Wabush Group [Member]        
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
Deconsolidation, Gain (Loss), Amount     134,700,000  
Other Current Assets [Member] | Canadian Entities [Member]        
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
Pre-Petition Financing   7,200,000    
Fair Value, Inputs, Level 3 [Member] | Other Current Assets [Member] | Canadian Entities [Member]        
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
Loans, Associated Interest and Accounts Receivable recognized in Consolidated Financials at Fair Value   51,600,000 $ 48,600,000  
Wabush Scully Mine Sale [Member]        
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
LOSS FROM DISCONTINUED OPERATIONS, net of tax   $ 31,400,000