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 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Dec. 31, 2015
Dec. 31, 2014
Stockholders' Equity Attributable to Parent $ (1,544.3)   $ (1,544.3)   $ (1,981.4)  
Stockholders' Equity Attributable to Noncontrolling Interest 143.8   143.8   169.8  
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest (1,400.5) $ (1,759.5) (1,400.5) $ (1,759.5) (1,811.6) $ (1,734.3)
NET INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS (25.8) 10.6 95.0 (689.0)    
INCOME (LOSS) ATTRIBUTABLE TO NONCONTROLLING INTEREST (2.0) (4.6) 23.5 (1.5)    
Net Income (Loss) (27.8) 6.0 118.5 (690.5)    
Other Comprehensive Income (Loss), Net of Tax 8.7 4.5 19.0 211.4    
TOTAL COMPREHENSIVE INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS (18.0) 14.4 111.8 (468.3)    
OTHER COMPREHENSIVE LOSS (INCOME) ATTRIBUTABLE TO THE NONCONTROLLING INTEREST 0.9 0.7 2.2 (9.3)    
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest     137.5 (479.1)    
Deconsolidation, Gain (Loss), Amount       528.2    
Stock and Other Incentive Plans     10.1 6.0    
Preferred share dividends       (38.4)    
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders     (48.8) (40.7)    
Undistributed Gains To Noncontrolling Interest     (2.9) (1.2)    
Cliffs Shareholders Equity [Member]            
Stockholders' Equity Attributable to Parent (1,544.3) (1,932.0) (1,544.3) (1,932.0) (1,981.4) (1,431.3)
NET INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS     95.0 (689.0)    
Other comprehensive income (loss)     16.8 220.7    
TOTAL COMPREHENSIVE INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS     111.8 (468.3)    
Deconsolidation, Gain (Loss), Amount       0.0    
Stock and Other Incentive Plans     10.1 6.0    
Preferred share dividends       (38.4)    
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders     0.0 0.0    
Undistributed Gains To Noncontrolling Interest     0.0 0.0    
Noncontrolling Interest [Member]            
Stockholders' Equity Attributable to Noncontrolling Interest $ 143.8 $ 172.5 143.8 172.5 $ 169.8 $ (303.0)
INCOME (LOSS) ATTRIBUTABLE TO NONCONTROLLING INTEREST     23.5 (1.5)    
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest     2.2 (9.3)    
OTHER COMPREHENSIVE LOSS (INCOME) ATTRIBUTABLE TO THE NONCONTROLLING INTEREST     25.7 (10.8)    
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     (48.8) (40.7)    
Undistributed Gains To Noncontrolling Interest     (2.9) $ (1.2)    
Common Stock [Member]            
Stock Issued During Period, Value, New Issues     315.2      
Common Stock [Member] | Cliffs Shareholders Equity [Member]            
Stock Issued During Period, Value, New Issues     315.2      
Common Stock [Member] | Noncontrolling Interest [Member]            
Stock Issued During Period, Value, New Issues     $ 0.0