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RELATED PARTIES (Summary Of Other Ownership Interests) (Details) | Sep. 30, 2015
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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%
Bloom Lake [Member] |
Related Party Transaction [Line Items] |
Noncontrolling Interest, Ownership Percentage by Parent | 82.80%
Other Noncurrent Assets [Member] | Hibbing [Member] |
Related Party Transaction [Line Items] |
Ownership interest, equity method investment | 23.00%

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