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
Mar. 31, 2016
Mar. 31, 2015
Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
INCOME (LOSS) FROM DISCONTINUED OPERATIONS, NET OF TAX $ 2.5 $ (928.5)  
Short-term assets of discontinued operations 0.5   $ 14.9
Short-term liabilities of discontinued operations 4.3   6.9
Depreciation, depletion and amortization 35.2 33.0  
Payments to Acquire Property, Plant, and Equipment 10.4 15.9  
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]      
INCOME (LOSS) FROM DISCONTINUED OPERATIONS, NET OF TAX (1.3) (75.7)  
Short-term assets of discontinued operations 0.5   14.9
Short-term liabilities of discontinued operations 4.3   6.9
Depreciation, depletion and amortization   3.2  
Payments to Acquire Property, Plant, and Equipment   2.5  
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]      
INCOME (LOSS) FROM DISCONTINUED OPERATIONS, NET OF TAX 3.8 (852.7)  
Short-term assets of discontinued operations 0.0   0.0
Short-term liabilities of discontinued operations 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]      
INCOME (LOSS) FROM DISCONTINUED OPERATIONS, NET OF TAX 0.0 (0.1)  
Short-term assets of discontinued operations 0.0   0.0
Short-term liabilities of discontinued operations 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]      
INCOME (LOSS) FROM DISCONTINUED OPERATIONS, NET OF TAX 3.8 (852.8)  
Short-term assets of discontinued operations 0.0   0.0
Short-term liabilities of discontinued operations $ 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   2.5  
Asset Impairment Charges, Cash Flows   $ 73.4