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RELATED PARTIES (Summary Of Other Ownership Interests) (Details) | Jun. 30, 2017 | Dec. 31, 2016
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Hibbing [Member] | Arcelor Mittal [Member] |  |
Related Party Transaction [Line Items] |  |
Ownership interest, equity method investment | 62.30% |
Hibbing [Member] | U. S. Steel Canada [Member] |  |
Related Party Transaction [Line Items] |  |
Ownership interest, equity method investment | 14.70% |
Empire [Member] |  |
Related Party Transaction [Line Items] |  |
Noncontrolling Interest, Ownership Percentage by Parent | 79.00% |
Empire [Member] | Arcelor Mittal [Member] |  |
Related Party Transaction [Line Items] |  |
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners | 21.00% |
Empire [Member] | U. S. Steel Canada [Member] |  |
Related Party Transaction [Line Items] |  |
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners | 0.00% |
Tilden [Member] |  |
Related Party Transaction [Line Items] |  |
Noncontrolling Interest, Ownership Percentage by Parent | 85.00% |
Tilden [Member] | Arcelor Mittal [Member] |  |
Related Party Transaction [Line Items] |  |
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners | 0.00% |
Tilden [Member] | U. S. Steel Canada [Member] |  |
Related Party Transaction [Line Items] |  |
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners | 15.00% |
Other Noncurrent Assets [Member] | Hibbing [Member] |  |
Related Party Transaction [Line Items] |  |
Ownership interest, equity method investment | 23.00% | 23.00%

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