Quarterly report pursuant to Section 13 or 15(d)

SHAREHOLDERS' EQUITY Schedule of Shareholders' Equity (Details)

v3.5.0.2
SHAREHOLDERS' EQUITY Schedule of Shareholders' Equity (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2016
Jun. 30, 2015
Jun. 30, 2016
Jun. 30, 2015
Dec. 31, 2015
Dec. 31, 2014
Stockholders' Equity Attributable to Parent $ (1,830.7)   $ (1,830.7)   $ (1,981.4)  
Stockholders' Equity Attributable to Noncontrolling Interest 151.8   151.8   169.8  
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest (1,678.9) $ (1,740.2) (1,678.9) $ (1,740.2) (1,811.6) $ (1,734.3)
NET INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS 12.8 60.2 120.8 (699.6)    
INCOME (LOSS) ATTRIBUTABLE TO NONCONTROLLING INTEREST 16.7 5.0 25.5 3.1    
Net Income (Loss) 29.5 65.2 146.3 (696.5)    
Other Comprehensive Income (Loss), Net of Tax 4.0 10.1 10.3 206.9    
TOTAL COMPREHENSIVE INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS 16.1 69.5 129.8 (482.7)    
OTHER COMPREHENSIVE LOSS (INCOME) ATTRIBUTABLE TO THE NONCONTROLLING INTEREST 0.7 0.8 1.3 (10.0)    
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest     156.6 (489.6)    
Deconsolidation, Gain (Loss), Amount       528.2    
Stock and Other Incentive Plans     6.5 3.0    
Preferred share dividends       (12.8)    
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders     (41.4)      
Undistributed Gains To Noncontrolling Interest     (3.4) (34.7)    
Cliffs Shareholders Equity [Member]            
Stockholders' Equity Attributable to Parent (1,830.7) (1,923.8) (1,830.7) (1,923.8) (1,981.4) (1,431.3)
NET INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS     120.8 (699.6)    
Other comprehensive income (loss)     9.0 216.9    
TOTAL COMPREHENSIVE INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS     129.8 (482.7)    
Deconsolidation, Gain (Loss), Amount       0.0    
Stock and Other Incentive Plans     6.5 3.0    
Preferred share dividends       (12.8)    
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders     0.0      
Undistributed Gains To Noncontrolling Interest     0.0 0.0    
Noncontrolling Interest [Member]            
Stockholders' Equity Attributable to Noncontrolling Interest $ 151.8 $ 183.6 151.8 183.6 $ 169.8 $ (303.0)
INCOME (LOSS) ATTRIBUTABLE TO NONCONTROLLING INTEREST     25.5 3.1    
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest     1.3 (10.0)    
OTHER COMPREHENSIVE LOSS (INCOME) ATTRIBUTABLE TO THE NONCONTROLLING INTEREST     26.8 (6.9)    
Deconsolidation, Gain (Loss), Amount       528.2    
Stock and Other Incentive Plans     0.0 0.0    
Preferred share dividends       0.0    
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders     (41.4)      
Undistributed Gains To Noncontrolling Interest     (3.4) $ (34.7)    
Common Stock [Member]            
Stock Issued During Period, Value, New Issues     14.4      
Common Stock [Member] | Cliffs Shareholders Equity [Member]            
Stock Issued During Period, Value, New Issues     14.4      
Common Stock [Member] | Noncontrolling Interest [Member]            
Stock Issued During Period, Value, New Issues     $ 0.0