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 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Dec. 31, 2012
Dec. 31, 2011
Stockholders' Equity Attributable to Parent $ 5,631.2   $ 5,631.2   $ 4,632.7  
Stockholders' Equity Attributable to Noncontrolling Interest 1,152.6   1,152.6   1,128.2  
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest 6,783.8 7,607.5 6,783.8 7,607.5 5,760.9 7,039.7
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS 146.0 258.0 253.0 633.8    
INCOME (LOSS) ATTRIBUTABLE TO NONCONTROLLING INTEREST 4.7 (16.3) (9.1) (31.9)    
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest 141.3 274.3 262.1 665.7    
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent (42.2) 239.0 69.0 636.5    
Other Comprehensive Income (Loss), Net of Tax (187.1) (17.5) (181.7) 5.7    
OTHER COMPREHENSIVE INCOME ATTRIBUTABLE TO THE NONCONTROLLING INTEREST (1.1) (1.5) (2.3) (3.0)    
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest     80.4 671.4    
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition     3.7 2.3    
Common and Preferred Shares dividends     (68.9)      
Common shares dividends       (128.8)    
Undistributed Gains To Noncontrolling Interest       8.6    
Capital Contribution By Noncontrolling Interest     13.0 22.3    
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests       (8.0)    
Cliffs Shareholders Equity [Member]
           
Stockholders' Equity Attributable to Parent 5,631.2 6,295.0 5,631.2 6,295.0 4,632.7 5,785.0
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS     253.0 633.8    
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent     (184.0) 2.7    
Comprehensive Income (Loss), Net of Tax, Attributable to Parent     69.0 636.5    
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition     3.7 2.3    
Common and Preferred Shares dividends     (68.9)      
Common shares dividends       (128.8)    
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 1,152.6 1,312.5 1,152.6 1,312.5 1,128.2 1,254.7
INCOME (LOSS) ATTRIBUTABLE TO NONCONTROLLING INTEREST     9.1 31.9    
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest     2.3 3.0    
OTHER COMPREHENSIVE INCOME ATTRIBUTABLE TO THE NONCONTROLLING INTEREST     11.4 34.9    
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition     0 0    
Common and Preferred Shares dividends     0      
Common shares dividends       0    
Undistributed Gains To Noncontrolling Interest       8.6    
Capital Contribution By Noncontrolling Interest     13.0 22.3    
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests       (8.0)    
Common Stock [Member]
           
Stock Issued During Period, Value, New Issues     263.4      
Common Stock [Member] | Cliffs Shareholders Equity [Member]
           
Stock Issued During Period, Value, New Issues     263.4      
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