Quarterly report pursuant to Section 13 or 15(d)

SHAREHOLDERS' EQUITY Schedule of Shareholders' Equity (Details)

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SHAREHOLDERS' EQUITY Schedule of Shareholders' Equity (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Dec. 31, 2012
Dec. 31, 2011
Stockholders' Equity Attributable to Parent $ 5,704.6   $ 4,632.7  
Dividends, Stock (32.8)      
Stockholders' Equity Attributable to Noncontrolling Interest 1,154.4   1,128.2  
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest 6,859.0 7,433.9 5,760.9 7,039.7
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS 107.0 375.8    
INCOME ATTRIBUTABLE TO NONCONTROLLING INTEREST (13.8) (15.6)    
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest 120.8 391.4    
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent 111.2 397.5    
Other Comprehensive Income (Loss), Net of Tax 5.4 23.2    
OTHER COMPREHENSIVE INCOME ATTRIBUTABLE TO THE NONCONTROLLING INTEREST (1.2) (1.5)    
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest 126.2 414.6    
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition (1.5) (2.8)    
Dividends, Common Stock   (39.7)    
Undistributed Gains To Noncontrolling Interest   7.8    
Capital Contribution By Noncontrolling Interest 11.2 22.3    
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests   (8.0)    
Cliffs Shareholders Equity [Member]
       
Stockholders' Equity Attributable to Parent 5,704.6 6,140.0 4,632.7 5,785.0
Dividends, Stock (32.8)      
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS 107.0 375.8    
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent 4.2 21.7    
Comprehensive Income (Loss), Net of Tax, Attributable to Parent 111.2 397.5    
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition (1.5) (2.8)    
Dividends, Common Stock   (39.7)    
Undistributed Gains To Noncontrolling Interest   0    
Capital Contribution By Noncontrolling Interest 0 0    
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests   0    
Noncontrolling Interest [Member]
       
Dividends, Stock 0      
Stockholders' Equity Attributable to Noncontrolling Interest 1,154.4 1,293.9 1,128.2 1,254.7
INCOME ATTRIBUTABLE TO NONCONTROLLING INTEREST 13.8 15.6    
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest 1.2 1.5    
OTHER COMPREHENSIVE INCOME ATTRIBUTABLE TO THE NONCONTROLLING INTEREST 15.0 17.1    
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition 0 0    
Dividends, Common Stock   0    
Undistributed Gains To Noncontrolling Interest   7.8    
Capital Contribution By Noncontrolling Interest 11.2 22.3    
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests   (8.0)    
Common Stock [Member]
       
Stock Issued During Period, Value, New Issues 263.7      
Common Stock [Member] | Cliffs Shareholders Equity [Member]
       
Stock Issued During Period, Value, New Issues 263.7      
Common Stock [Member] | Noncontrolling Interest [Member]
       
Stock Issued During Period, Value, New Issues 0      
Preferred Class A [Member]
       
Stock Issued During Period, Value, New Issues 731.3      
Preferred Class A [Member] | Cliffs Shareholders Equity [Member]
       
Stock Issued During Period, Value, New Issues 731.3      
Preferred Class A [Member] | Noncontrolling Interest [Member]
       
Stock Issued During Period, Value, New Issues $ 0