RELATED PARTIES (Narrative) (Details) $ in Millions |
3 Months Ended | 9 Months Ended |
|---|---|---|
|
Sep. 30, 2017
USD ($)
|
Sep. 30, 2018
USD ($)
Facility
|
|
| Segment Reporting Information [Line Items] | 听 | 听 |
| Noncontrolling Interest, Ownership Percentage by Parent | 听 | 100.00% |
| Purchase of Noncontrolling Interest | $ (105.0) | 听 |
| U.S. Iron Ore [Member] | 听 | 听 |
| Segment Reporting Information [Line Items] | 听 | 听 |
| Number of mines (in number of facilities) | Facility | 听 | 4 |
| Joint Venture Partners [Member] | U.S. Iron Ore [Member] | 听 | 听 |
| Segment Reporting Information [Line Items] | 听 | 听 |
| Number of mines (in number of facilities) | Facility | 听 | 1 |
| Empire | 听 | 听 |
| Segment Reporting Information [Line Items] | 听 | 听 |
| Noncontrolling Interest, Ownership Percentage by Parent | 听 | 100.00% |
| Purchase of Noncontrolling Interest | 听 | $ 132.7 |
| Noncontrolling Interest Purchase, Installment Amount | 听 | 44.2 |
| Other Noncurrent Liabilities [Member] | Empire | 听 | 听 |
| Segment Reporting Information [Line Items] | 听 | 听 |
| Noncontrolling Interest Purchase, Installment Amount | 听 | $ 44.2 |
| X | ||||||||||
- Definition Noncontrolling Interest Purchase, Installment Amount No definition available.
|
| X | ||||||||||
- Definition Number of mines No definition available.
|
| X | ||||||||||
- Definition Purchase of Noncontrolling Interest No definition available.
|
| X | ||||||||||
- Definition The parent entity's interest in net assets of the subsidiary, expressed as a percentage. No definition available.
|
| 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
|