Quarterly report pursuant to Section 13 or 15(d)

RELATED PARTIES (Narrative) (Details)

v3.4.0.3
RELATED PARTIES (Narrative) (Details)
$ in Millions
3 Months Ended
Mar. 31, 2016
USD ($)
Facility
Dec. 31, 2015
USD ($)
Segment Reporting Information [Line Items]    
Due from Related Parties, Current $ 10.7 $ 15.8
Due to Related Parties, Current $ 17.5 $ 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 $ 11.1  
Recorded Distributions of Partners' Equity Amounts $ 17.0