RELATED PARTIES (Summary Of Other Ownership Interests) (Details) |
Dec. 31, 2018 |
Dec. 31, 2017 |
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| Related Party Transaction [Line Items] | Ìý | Ìý |
| Noncontrolling Interest, Ownership Percentage by Parent | 100.00% | Ìý |
| Hibbing [Member] | Arcelor Mittal [Member] | Ìý | Ìý |
| Related Party Transaction [Line Items] | Ìý | Ìý |
| Ownership interest, equity method investment | 62.30% | Ìý |
| Hibbing [Member] | U. S. Steel Canada [Member] | Ìý | Ìý |
| Related Party Transaction [Line Items] | Ìý | Ìý |
| Ownership interest, equity method investment | 14.70% | Ìý |
| Empire [Member] | Ìý | Ìý |
| Related Party Transaction [Line Items] | Ìý | Ìý |
| Noncontrolling Interest, Ownership Percentage by Parent | Ìý | 100.00% |
| Tilden [Member] | Ìý | Ìý |
| Related Party Transaction [Line Items] | Ìý | Ìý |
| Noncontrolling Interest, Ownership Percentage by Parent | Ìý | 100.00% |
| Investments in Ventures [Member] | Hibbing [Member] | Ìý | Ìý |
| Related Party Transaction [Line Items] | Ìý | Ìý |
| Ownership interest, equity method investment | 23.00% | Ìý |
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- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition The parent entity's interest in net assets of the subsidiary, expressed as a percentage. No definition available.
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
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