Quarterly report pursuant to Section 13 or 15(d)

DISCONTINUED OPERATIONS Schedule of Disposal Groups, including Discontinued Operations, Income Statement, Balance Sheet and Cash Flows (Details)

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DISCONTINUED OPERATIONS Schedule of Disposal Groups, including Discontinued Operations, Income Statement, Balance Sheet and Cash Flows (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
LOSS FROM DISCONTINUED OPERATIONS, NET OF TAX $ (2.7) $ (43.9) $ (0.6) $ (869.0)  
Short-term assets of discontinued operations 0.0   0.0   $ 14.9
Short-term liabilities of discontinued operations 5.5   5.5   6.9
Depreciation, depletion and amortization 26.8 35.6 88.9 99.1  
Payments to Acquire Property, Plant, and Equipment     45.8 57.9  
Asset Impairment Charges, Cash Flows     0.0 76.6  
North American Coal [Member]          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Disposal Group, Including Discontinued Operation, Liabilities 5.5   5.5   6.9
LOSS FROM DISCONTINUED OPERATIONS, NET OF TAX (1.8) (29.8) (3.8) (137.0)  
Short-term assets of discontinued operations 0.0   0.0   14.9
Short-term liabilities of discontinued operations         6.9
Depreciation, depletion and amortization       3.2  
Payments to Acquire Property, Plant, and Equipment       13.1  
Asset Impairment Charges, Cash Flows       73.4  
Eastern Canadian Iron Ore [Member]          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
LOSS FROM DISCONTINUED OPERATIONS, NET OF TAX (0.9) (14.1) 3.2 (731.9)  
Short-term assets of discontinued operations 0.0   0.0   0.0
Short-term liabilities of discontinued operations 0.0   0.0   0.0
Depreciation, depletion and amortization       0.0  
Payments to Acquire Property, Plant, and Equipment       0.0  
Asset Impairment Charges, Cash Flows       0.0  
Other Canadian Operations [Member]          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
LOSS FROM DISCONTINUED OPERATIONS, NET OF TAX 0.0 0.0 0.0 (0.1)  
Short-term assets of discontinued operations 0.0   0.0   0.0
Short-term liabilities of discontinued operations 0.0   0.0   0.0
Depreciation, depletion and amortization       0.0  
Payments to Acquire Property, Plant, and Equipment       0.0  
Asset Impairment Charges, Cash Flows       0.0  
Canadian Entities [Member]          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
LOSS FROM DISCONTINUED OPERATIONS, NET OF TAX (0.9) $ (14.1) 3.2 (732.0)  
Short-term assets of discontinued operations 0.0   0.0   0.0
Short-term liabilities of discontinued operations $ 0.0   $ 0.0   $ 0.0
Depreciation, depletion and amortization       0.0  
Payments to Acquire Property, Plant, and Equipment       0.0  
Asset Impairment Charges, Cash Flows       0.0  
Discontinued Operations [Member]          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Depreciation, depletion and amortization       3.2  
Payments to Acquire Property, Plant, and Equipment       13.1  
Asset Impairment Charges, Cash Flows       $ 73.4