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 9 Months Ended
Sep. 30, 2016
USD ($)
Sep. 30, 2015
USD ($)
Sep. 30, 2016
USD ($)
Facility
Sep. 30, 2015
USD ($)
Dec. 31, 2015
USD ($)
Segment Reporting Information [Line Items]          
Due from Related Parties, Current $ 52.2   $ 52.2   $ 15.8
Due to Related Parties, Current 7.4   $ 7.4   $ 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 41.4 $ 31.7 $ 41.4 $ 31.7  
Recorded Distributions of Partners' Equity Amounts $ 7.4 $ 9.0 $ 48.8 $ 40.7