Quarterly report pursuant to Section 13 or 15(d)

GOODWILL AND OTHER INTANGIBLE ASSETS AND LIABILITIES (Narrative) (Details)

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GOODWILL AND OTHER INTANGIBLE ASSETS AND LIABILITIES (Narrative) (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2016
Cost of Sales [Member]          
Goodwill [Line Items]          
Amortization expense relating to intangible assets $ 0.4 $ 1.2 $ 1.0 $ 2.6  
U.S. Iron Ore [Member]          
Goodwill [Line Items]          
Goodwill $ 2.0   $ 2.0   $ 2.0