BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Schedule Of Subsidiaries) (Details) |
6 Months Ended |
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Jun. 30, 2019 | |
| Related Party Transaction [Line Items] | |
| Entity Address, State or Province | OH |
| Northshore | |
| Related Party Transaction [Line Items] | |
| Entity Address, State or Province | MN |
| United Taconite | |
| Related Party Transaction [Line Items] | |
| Entity Address, State or Province | MN |
| Tilden | |
| Related Party Transaction [Line Items] | |
| Entity Address, State or Province | MI |
| Empire | |
| Related Party Transaction [Line Items] | |
| Entity Address, State or Province | MI |
| Metallics | |
| Related Party Transaction [Line Items] | |
| Entity Address, State or Province | OH |
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