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
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Cost of Sales [Member]      
Goodwill [Line Items]      
Amortization expense relating to intangible assets $ 2.6 $ 0.6  
U.S. Iron Ore [Member]      
Goodwill [Line Items]      
Goodwill $ 2.0   $ 2.0