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 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Dec. 31, 2012
Dec. 31, 2011
Stockholders' Equity Attributable to Parent $ 5,779.7   $ 5,779.7   $ 4,632.7  
Stockholders' Equity Attributable to Noncontrolling Interest 1,154.9   1,154.9   1,128.2  
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest 6,934.6 7,689.2 6,934.6 7,689.2 5,760.9 7,039.7
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS 117.2 85.1 370.2 719.0    
INCOME (LOSS) ATTRIBUTABLE TO NONCONTROLLING INTEREST (3.3) (6.7) 5.8 25.2    
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest 113.9 78.4 376.0 744.2    
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent 178.4 123.9 247.4 760.6    
Other Comprehensive Income (Loss), Net of Tax 62.1 40.3 (119.6) 46.1    
OTHER COMPREHENSIVE INCOME ATTRIBUTABLE TO THE NONCONTROLLING INTEREST (0.9) (1.5) (3.2) (4.5)    
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest     256.4 790.3    
Stock and Other Incentive Plans     9.6 9.0    
Common and Preferred Shares dividends     (104.7)      
Common shares dividends       (217.8)    
Undistributed Gains To Noncontrolling Interest       11.3    
Capital Contribution By Noncontrolling Interest     17.7 64.7    
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests       (8.0)    
Cliffs Shareholders Equity [Member]
            
Stockholders' Equity Attributable to Parent 5,779.7 6,336.8 5,779.7 6,336.8 4,632.7 5,785.0
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS     370.2 719.0    
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent     (122.8) 41.6    
Other Comprehensive Income (Loss), Net of Tax       41.6    
Comprehensive Income (Loss), Net of Tax, Attributable to Parent     247.4 760.6    
Stock and Other Incentive Plans     9.6 9.0    
Common and Preferred Shares dividends     (104.7)      
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]
            
Stockholders' Equity Attributable to Noncontrolling Interest 1,154.9 1,352.4 1,154.9 1,352.4 1,128.2 1,254.7
INCOME (LOSS) ATTRIBUTABLE TO NONCONTROLLING INTEREST     5.8 25.2    
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest     3.2 4.5    
OTHER COMPREHENSIVE INCOME ATTRIBUTABLE TO THE NONCONTROLLING INTEREST     9.0 29.7    
Stock and Other Incentive Plans     0 0    
Common and Preferred Shares dividends     0      
Common shares dividends       0    
Undistributed Gains To Noncontrolling Interest       11.3    
Capital Contribution By Noncontrolling Interest     17.7 64.7    
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests       (8.0)    
Common Stock [Member]
            
Stock Issued During Period, Value, New Issues     285.3      
Common Stock [Member] | Cliffs Shareholders Equity [Member]
            
Stock Issued During Period, Value, New Issues     285.3      
Common shares dividends       (217.8)    
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     709.4      
Preferred Class A [Member] | Cliffs Shareholders Equity [Member]
            
Stock Issued During Period, Value, New Issues     709.4      
Preferred Class A [Member] | Noncontrolling Interest [Member]
            
Stock Issued During Period, Value, New Issues     $ 0