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, 2014
Mar. 31, 2013
Dec. 31, 2013
Dec. 31, 2012
Stockholders' Equity Attributable to Parent $ 6,019.5   $ 6,069.5  
Stockholders' Equity Attributable to Noncontrolling Interest 816.1   814.8  
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest 6,835.6 6,859.0 6,884.3 5,760.9
NET INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS (70.3) 107.0    
INCOME (LOSS) ATTRIBUTABLE TO NONCONTROLLING INTEREST (0.4) 13.8    
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest (70.7) 120.8    
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent (12.5) 111.2    
Other Comprehensive Income (Loss), Net of Tax 58.3 5.4    
OTHER COMPREHENSIVE INCOME ATTRIBUTABLE TO THE NONCONTROLLING INTEREST (0.5) (1.2)    
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest (12.4) 126.2    
Stock and Other Incentive Plans (1.4) (1.5)    
Common and preferred share dividends (36.1) (32.8)    
Undistributed Gains To Noncontrolling Interest 1.2 9.8    
Capital Contribution By Noncontrolling Interest   1.4    
Cliffs Shareholders Equity [Member]
       
Stockholders' Equity Attributable to Parent 6,019.5 5,704.6 6,069.5 4,632.7
NET INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS (70.3) 107.0    
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent 57.8 4.2    
Comprehensive Income (Loss), Net of Tax, Attributable to Parent (12.5) 111.2    
Stock and Other Incentive Plans (1.4) (1.5)    
Common and preferred share dividends (36.1) (32.8)    
Undistributed Gains To Noncontrolling Interest 0 0    
Capital Contribution By Noncontrolling Interest   0    
Noncontrolling Interest [Member]
       
Stockholders' Equity Attributable to Noncontrolling Interest 816.1 1,154.4 814.8 1,128.2
INCOME (LOSS) ATTRIBUTABLE TO NONCONTROLLING INTEREST (0.4) 13.8    
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest 0.5 1.2    
OTHER COMPREHENSIVE INCOME ATTRIBUTABLE TO THE NONCONTROLLING INTEREST 0.1 15.0    
Stock and Other Incentive Plans 0 0    
Common and preferred share dividends 0 0    
Undistributed Gains To Noncontrolling Interest 1.2 9.8    
Capital Contribution By Noncontrolling Interest   1.4    
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