Annual report pursuant to Section 13 and 15(d)

QUARTERLY RESULTS OF OPERATIONS (Details)

v3.3.1.900
QUARTERLY RESULTS OF OPERATIONS (Details) - USD ($)
shares in Millions, $ in Millions
 3 Months Ended 12 Months Ended
Dec. 31, 2014
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount 25.2 25.3 25.2 0.0
Antidilutive Incremental Common Shares Excluded and Attributable to Share-based Payment Arrangements 0.5   0.7  
Gain Contingency on North American Coal Sale   $ 50.0    
Loss (gain) on sale of North American Coal mines $ 419.6   $ 155.0  
Sale Price of CLCC Assets 174.0   174.0  
Proceeds from sale of Cliffs Logan County Coal 155.0      
Income Tax Expense (Benefit) (207.3) 169.3 (86.0) $ 237.6
Asset Impairment Charges   $ 3.3 $ 635.5 $ 14.3
Minimum [Member]        
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount   25.2    
Antidilutive Incremental Common Shares Excluded and Attributable to Share-based Payment Arrangements   0.1    
Maximum [Member]        
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount   25.6    
Antidilutive Incremental Common Shares Excluded and Attributable to Share-based Payment Arrangements   0.3    
Continuing Operations [Member]        
Asset Impairment Charges 256.9      
Discontinued Operations [Member]        
Asset Impairment Charges $ 1,000.0