Quarterly report pursuant to Section 13 or 15(d)

RELATED PARTIES (Narrative) (Details)

v3.5.0.2
RELATED PARTIES (Narrative) (Details)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2016
USD ($)
Jun. 30, 2016
USD ($)
Facility
Jun. 30, 2015
USD ($)
Dec. 31, 2015
USD ($)
Segment Reporting Information [Line Items]        
Due from Related Parties, Current $ 57.9 $ 57.9   $ 15.8
Due to Related Parties, Current 25.0 $ 25.0   $ 14.5
U.S. Iron Ore [Member]        
Segment Reporting Information [Line Items]        
Number of mines (in number of facilities) | Facility   5    
Joint Venture Partners [Member] | U.S. Iron Ore [Member]        
Segment Reporting Information [Line Items]        
Number of mines (in number of facilities) | Facility   3    
Empire [Member] | Arcelor Mittal [Member]        
Segment Reporting Information [Line Items]        
Paid Distributions of Partners' Equity Amounts 17.0 $ 17.0 $ 17.1  
Recorded Distributions of Partners' Equity Amounts $ 24.4 $ 41.4 $ 31.7