Quarterly report pursuant to Section 13 or 15(d)

Shareholders' Equity and Comprehensive income (Changes in Comprehensive Income) (Details)

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Shareholders' Equity and Comprehensive income (Changes in Comprehensive Income) (Details) (USD $)
In Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2011
Jun. 30, 2010
Jun. 30, 2011
Jun. 30, 2010
Beginning Balance     $ 3,845.9  
Beginning Balance     (7.2)  
Beginning Balance     3,838.7  
Net income 407.7 260.7 831.1 338.1
Net income 18.3 (0.1) 18.2 (0.1)
Net income 426.0 260.6 849.3 338.0
Total comprehensive income 433.7 185.8 881.2 319.4
Ending Balance 5,546.2   5,546.2  
Ending Balance 973.8   973.8  
Ending Balance 6,520.0   6,520.0  
Cliffs Shareholders' Equity [Member]
        
Beginning Balance     3,845.9  
Net income     831.1  
Other comprehensive income     50.1  
Total comprehensive income     881.2  
Equity offering     853.7  
Purchase of additional noncontrolling interest     0.3  
Stock and other incentive plans     3.1  
Common stock dividends     (38.0)  
Ending Balance 5,546.2   5,546.2  
Non- Controlling Interest [Member]
        
Beginning Balance     (7.2)  
Net income     18.2  
Other comprehensive income     0.9  
Total comprehensive income     19.1  
Purchase of subsidiary shares from noncontrolling interest     4.5  
Undistributed gains to noncontrolling interest     9.6  
Capital contribution by noncontrolling interest to subsidiary     0.2  
Acquisition of controlling interest     947.6  
Ending Balance 973.8   973.8  
Total Comprehensive Income [Member]
        
Beginning Balance     3,838.7  
Net income     849.3  
Other comprehensive income     51.0  
Total comprehensive income     900.3  
Equity offering     853.7  
Purchase of additional noncontrolling interest     0.3  
Stock and other incentive plans     3.1  
Common stock dividends     (38.0)  
Purchase of subsidiary shares from noncontrolling interest     4.5  
Undistributed gains to noncontrolling interest     9.6  
Capital contribution by noncontrolling interest to subsidiary     0.2  
Acquisition of controlling interest     947.6  
Ending Balance $ 6,520.0   $ 6,520.0