RELATED PARTIES (Summary Of Other Ownership Interests) (Details) - Hibbing [Member] |
Sep. 30, 2017 |
Dec. 31, 2016 |
|---|---|---|
| Arcelor Mittal [Member] | 听 | 听 |
| Related Party Transaction [Line Items] | 听 | 听 |
| Ownership interest, equity method investment | 62.30% | 听 |
| U. S. Steel Canada [Member] | 听 | 听 |
| Related Party Transaction [Line Items] | 听 | 听 |
| Ownership interest, equity method investment | 14.70% | 听 |
| Other Noncurrent Assets [Member] | 听 | 听 |
| Related Party Transaction [Line Items] | 听 | 听 |
| Ownership interest, equity method investment | 23.00% | 23.00% |
| X | ||||||||||
- 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://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
- 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.
|
| X | ||||||||||
- Details
|
| X | ||||||||||
- Details
|
| X | ||||||||||
- Details
|
| X | ||||||||||
- Details
|