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Quarterly report pursuant to Section 13 or 15(d)

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details)

v3.19.1
BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details) - Hibbing [Member] - USD ($)
$ in Millions
Mar. 31, 2019
Dec. 31, 2018
Investments in Ventures [Member] Ìý Ìý
Related Party Transaction [Line Items] Ìý Ìý
Ownership interest, equity method investment 23.00% 23.00%
Other Noncurrent Liabilities [Member] Ìý Ìý
Related Party Transaction [Line Items] Ìý Ìý
Equity Method Investments $ 10.8 $ 15.4