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BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Schedule Of Subsidiaries) (Details) | 9 Months Ended |
--- | --- | ---
Sep. 30, 2017 | Dec. 31, 2016
Northshore [Member] |  |
Related Party Transaction [Line Items] |  |
Entity Address, State or Province | Minnesota |
Noncontrolling Interest, Ownership Percentage by Parent | 100.00% |
Segment Reporting Information, Description of Products and Services | Iron Ore |
United Taconite [Member] |  |
Related Party Transaction [Line Items] |  |
Entity Address, State or Province | Minnesota |
Noncontrolling Interest, Ownership Percentage by Parent | 100.00% |
Segment Reporting Information, Description of Products and Services | Iron Ore |
Tilden [Member] |  |
Related Party Transaction [Line Items] |  |
Entity Address, State or Province | Michigan |
Noncontrolling Interest, Ownership Percentage by Parent | 100.00% | 85.00%
Segment Reporting Information, Description of Products and Services | Iron Ore |
Empire [Member] |  |
Related Party Transaction [Line Items] |  |
Entity Address, State or Province | Michigan |
Noncontrolling Interest, Ownership Percentage by Parent | 100.00% | 79.00%
Segment Reporting Information, Description of Products and Services | Iron Ore |
Koolyanobbing [Member] |  |
Related Party Transaction [Line Items] |  |
Entity Address, State or Province | Western Australia |
Noncontrolling Interest, Ownership Percentage by Parent | 100.00% |
Segment Reporting Information, Description of Products and Services | Iron Ore |

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- Definition Description of the types of products and services from which the reportable segment derives its revenue. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 21 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8721-108599 + Details
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