BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Schedule Of Subsidiaries) (Details) |
9 Months Ended |
|---|---|
Sep. 30, 2018 | |
| Northshore | |
| Related Party Transaction [Line Items] | |
| Entity Address, State or Province | Minnesota |
| United Taconite | |
| Related Party Transaction [Line Items] | |
| Entity Address, State or Province | Minnesota |
| Tilden | |
| Related Party Transaction [Line Items] | |
| Entity Address, State or Province | Michigan |
| Empire | |
| Related Party Transaction [Line Items] | |
| Entity Address, State or Province | Michigan |
| Koolyanobbing | |
| Related Party Transaction [Line Items] | |
| Entity Address, State or Province | Western Australia |
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