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RELATED PARTIES (Summary Of Other Ownership Interests) (Details)
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Mar. 31, 2013
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Empire [Member]
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| Related Party Transaction [Line Items] | ||||
| Ownership Interest | 79.00% | |||
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Tilden [Member]
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| Related Party Transaction [Line Items] | ||||
| Ownership Interest | 85.00% | |||
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Bloom Lake [Member]
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| Related Party Transaction [Line Items] | ||||
| Ownership Interest | 75.00% | |||
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Arcelor Mittal [Member] | Empire [Member]
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| Related Party Transaction [Line Items] | ||||
| Ownership Interest | 21.00% | |||
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Arcelor Mittal [Member] | Tilden [Member]
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| Related Party Transaction [Line Items] | ||||
| Ownership Interest | 0.00% | |||
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Arcelor Mittal [Member] | Hibbing [Member]
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| Related Party Transaction [Line Items] | ||||
| Ownership Interest | 62.30% | |||
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Arcelor Mittal [Member] | Bloom Lake [Member]
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| Related Party Transaction [Line Items] | ||||
| Ownership Interest | 0.00% | |||
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U. S. Steel Canada [Member] | Empire [Member]
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| Related Party Transaction [Line Items] | ||||
| Ownership Interest | 0.00% | |||
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U. S. Steel Canada [Member] | Tilden [Member]
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| Related Party Transaction [Line Items] | ||||
| Ownership Interest | 15.00% | |||
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U. S. Steel Canada [Member] | Hibbing [Member]
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| Related Party Transaction [Line Items] | ||||
| Ownership Interest | 14.70% | |||
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U. S. Steel Canada [Member] | Bloom Lake [Member]
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| Related Party Transaction [Line Items] | ||||
| Ownership Interest | 0.00% | |||
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WISCO [Member] | Empire [Member]
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| Related Party Transaction [Line Items] | ||||
| Ownership Interest | 0.00% | |||
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WISCO [Member] | Tilden [Member]
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| Related Party Transaction [Line Items] | ||||
| Ownership Interest | 0.00% | |||
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WISCO [Member] | Hibbing [Member]
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| Related Party Transaction [Line Items] | ||||
| Ownership Interest | 0.00% | |||
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WISCO [Member] | Bloom Lake [Member]
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| Related Party Transaction [Line Items] | ||||
| Ownership Interest | 25.00% | |||
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Equity Method Investments [Member] | Hibbing [Member] | Hibbing [Member]
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| Related Party Transaction [Line Items] | ||||
| Ownership interest, equity method investment | 23.00% | [1] | ||
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