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RELATED PARTIES (Summary Of Other Ownership Interests) (Details) - Hibbing [Member] | Jun. 30, 2019 | Dec. 31, 2018
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Related Party Transaction [Line Items] |  |
Ownership interest, equity method investment | 23.00% | 23.00%
Arcelor Mittal [Member] |  |
Related Party Transaction [Line Items] |  |
Ownership interest, equity method investment | 62.30% |
U. S. Steel Canada [Member] |  |
Related Party Transaction [Line Items] |  |
Ownership interest, equity method investment | 14.70% |

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