BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Schedule Of Subsidiaries) (Details) |
3 Months Ended |
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Mar. 31, 2018 | |
| Northshore [Member] | |
| Related Party Transaction [Line Items] | |
| Entity Address, State or Province | Minnesota |
| United Taconite [Member] | |
| Related Party Transaction [Line Items] | |
| Entity Address, State or Province | Minnesota |
| Tilden [Member] | |
| Related Party Transaction [Line Items] | |
| Entity Address, State or Province | Michigan |
| Empire [Member] | |
| Related Party Transaction [Line Items] | |
| Entity Address, State or Province | Michigan |
| Koolyanobbing [Member] | |
| Related Party Transaction [Line Items] | |
| Entity Address, State or Province | Western Australia |
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