BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Schedule Of Subsidiaries) (Details) |
3 Months Ended |
|---|---|
Mar. 31, 2019 | |
| 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 |
| Metallics [Member] | |
| Related Party Transaction [Line Items] | |
| Entity Address, State or Province | Ohio |
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