Quarterly report pursuant to Section 13 or 15(d)

RELATED PARTIES (Narrative) (Details)

v3.3.0.814
RELATED PARTIES (Narrative) (Details)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2015
USD ($)
Sep. 30, 2015
USD ($)
Facility
Dec. 31, 2014
USD ($)
Segment Reporting Information [Line Items]      
Due from Related Parties, Current $ 12.2 $ 12.2 $ 127.6
Due to Related Parties, Current 10.9 $ 10.9 $ 11.8
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]      
Recorded Distributions of Partners' Equity Amounts 9.0 $ 40.7  
Paid Distributions of Partners' Equity Amounts $ 31.7 $ 31.7