Annual report pursuant to Section 13 and 15(d)

QUARTERLY RESULTS OF OPERATIONS (Narrative) (Details)

v2.4.0.6
QUARTERLY RESULTS OF OPERATIONS (Narrative) (Details)
12 Months Ended 3 Months Ended 9 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended
Dec. 31, 2012
USD ($)
Dec. 31, 2011
USD ($)
Dec. 31, 2010
USD ($)
Sep. 30, 2011
Empire [Member]
USD ($)
Sep. 30, 2011
Empire [Member]
USD ($)
Dec. 31, 2011
Empire [Member]
USD ($)
Sep. 30, 2011
Arcelor Mittal [Member]
USD ($)
Dec. 31, 2011
Arcelor Mittal [Member]
USD ($)
Dec. 31, 2012
Empire [Member]
Sep. 30, 2011
Empire [Member]
Dec. 31, 2012
Sonoma [Member]
Asia Pacific Coal [Member]
AUD
Dec. 31, 2012
Bloom Lake [Member]
USD ($)
Dec. 31, 2012
Wabush [Member]
USD ($)
Dec. 31, 2012
Wabush [Member]
USD ($)
Feb. 28, 2010
Wabush [Member]
Dec. 31, 2012
MRRT Starting Base Deferred Tax Asset, Unrealizable [Member]
USD ($)
Dec. 31, 2012
Deferred Tax Asset, Alternative Minimum Tax Credit Not Utilized [Member]
USD ($)
Immaterial Errors                                  
Noncontrolling interest                   21.00%              
Adjustment to record noncontrolling interest       $ 84,000,000 $ 84,000,000                        
Adjustment to record noncontrolling interest, increase to Income from Continuing Operations       16,100,000 16,100,000                        
Adjustment to record noncontrolling interest, decrease to Net Income Attributable to Cliffs Shareholders       67,900,000 67,900,000                        
Error Correction to Earnings Per Share Basic       $ (0.47) $ (0.49)                        
Error Correction To Earnings Per Share, Diluted       $ (0.47) $ (0.48)                        
Adjustment to record noncontrolling interest, decrease in Retained Earnings           67,900,000                      
Adjustment to record noncontrolling interest, increase in Noncontrolling Interest           84,000,000                      
Reclassification of amounts to Product revenues       46,000,000   46,000,000 54,100,000 54,100,000                  
Discontinued Operations                                  
Ownership Interest                 79.00%   45.00%       73.20%    
Proceeds from sale of economic interest                     141,000,000            
Goodwill impairment 1,000,000,000 27,800,000                   997,300,000 2,700,000 2,700,000      
Impairment of goodwill and other long-lived assets 1,049,900,000 27,800,000 0                   49,900,000        
Income tax expense $ 255,900,000 $ 407,700,000 $ 282,500,000                         $ 314,700,000 $ 226,400,000