Annual report pursuant to Section 13 and 15(d)

RELATED PARTIES (Narrative) (Details)

v3.6.0.2
RELATED PARTIES (Narrative) (Details)
$ in Millions
12 Months Ended
Dec. 31, 2016
USD ($)
Facility
Dec. 31, 2015
USD ($)
Segment Reporting Information [Line Items]    
Due from Related Parties, Current $ 73.8 $ 15.8
Due to Related Parties, Current $ 8.7 14.5
U.S. Iron Ore [Member]    
Segment Reporting Information [Line Items]    
Number Of Mines | Facility 4  
Joint Venture Partners [Member] | U.S. Iron Ore [Member]    
Segment Reporting Information [Line Items]    
Number Of Mines | Facility 2  
Empire [Member] | Arcelor Mittal [Member]    
Segment Reporting Information [Line Items]    
Recorded Distributions of Partners' Equity Amounts $ 57.5 51.7
Paid Distributions of Partners' Equity Amounts $ 48.8 $ 40.6