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Quarterly report pursuant to Section 13 or 15(d)

RELATED PARTIES (Narrative) (Details)

v3.10.0.1
RELATED PARTIES (Narrative) (Details)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2017
USD ($)
Sep. 30, 2018
USD ($)
Facility
Segment Reporting Information [Line Items] Ìý Ìý
Noncontrolling Interest, Ownership Percentage by Parent Ìý 100.00%
Purchase of Noncontrolling Interest $ (105.0) Ìý
U.S. Iron Ore [Member] Ìý Ìý
Segment Reporting Information [Line Items] Ìý Ìý
Number of mines (in number of facilities) | Facility Ìý 4
Joint Venture Partners [Member] | U.S. Iron Ore [Member] Ìý Ìý
Segment Reporting Information [Line Items] Ìý Ìý
Number of mines (in number of facilities) | Facility Ìý 1
Empire Ìý Ìý
Segment Reporting Information [Line Items] Ìý Ìý
Noncontrolling Interest, Ownership Percentage by Parent Ìý 100.00%
Purchase of Noncontrolling Interest Ìý $ 132.7
Noncontrolling Interest Purchase, Installment Amount Ìý 44.2
Other Noncurrent Liabilities [Member] | Empire Ìý Ìý
Segment Reporting Information [Line Items] Ìý Ìý
Noncontrolling Interest Purchase, Installment Amount Ìý $ 44.2