SEGMENT REPORTING (Schedule of Segment Reporting Information) (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||||||
|---|---|---|---|---|---|---|---|---|
Sep. 30, 2019 |
Jun. 30, 2019 |
Mar. 31, 2019 |
Sep. 30, 2018 |
Jun. 30, 2018 |
Mar. 31, 2018 |
Sep. 30, 2019 |
Sep. 30, 2018 |
|
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Revenues | $ 555.6 | Ìý | Ìý | $ 741.8 | Ìý | Ìý | $ 1,455.8 | $ 1,636.1 |
| SALES MARGIN | 154.9 | Ìý | Ìý | 261.6 | Ìý | Ìý | 448.8 | 607.6 |
| NET INCOME | 90.9 | $ 160.8 | $ (22.1) | 437.8 | $ 165.1 | $ (84.3) | 229.6 | 518.6 |
| Interest expense, net | (25.3) | Ìý | Ìý | (29.5) | Ìý | Ìý | (76.5) | (93.1) |
| Income tax expense | 4.8 | Ìý | Ìý | 0.5 | Ìý | Ìý | 23.1 | 14.4 |
| Depreciation, depletion and amortization | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 63.1 | 68.6 |
| Depreciation, Depletion and Amortization excluding Depreciation, Amortization and Depletion expense for Discontinued Operations | 22.2 | Ìý | Ìý | 19.2 | Ìý | Ìý | 63.1 | 53.4 |
| EBITDA | 143.3 | Ìý | Ìý | 487.2 | Ìý | Ìý | 392.6 | 697.1 |
| Impact of discontinued operations | (0.9) | Ìý | Ìý | 238.0 | Ìý | Ìý | (1.5) | 102.8 |
| Gain (loss) on extinguishment of debt | Ìý | Ìý | Ìý | 0.0 | Ìý | Ìý | (18.2) | 0.2 |
| Adjusted EBITDA | 144.1 | Ìý | Ìý | 250.3 | Ìý | Ìý | 413.7 | 578.3 |
| Property, Plant and Equipment, Additions | 184.7 | Ìý | Ìý | 92.6 | Ìý | Ìý | 505.6 | 241.9 |
| Mining and Pelletizing [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Revenues | 555.6 | Ìý | Ìý | 741.8 | Ìý | Ìý | 1,455.8 | 1,636.1 |
| SALES MARGIN | 154.9 | Ìý | Ìý | 261.6 | Ìý | Ìý | 448.8 | 607.6 |
| Depreciation, depletion and amortization | 20.8 | Ìý | Ìý | 17.8 | Ìý | Ìý | 58.9 | 49.2 |
| EBITDA | 177.5 | Ìý | Ìý | 273.1 | Ìý | Ìý | 494.9 | 641.6 |
| Adjusted EBITDA | 182.7 | Ìý | Ìý | 279.5 | Ìý | Ìý | 510.7 | 657.9 |
| Property, Plant and Equipment, Additions | 22.1 | Ìý | Ìý | 51.8 | Ìý | Ìý | 104.5 | 97.2 |
| Metallics [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Revenues | 0.0 | Ìý | Ìý | Ìý | Ìý | Ìý | 0.0 | Ìý |
| SALES MARGIN | 0.0 | Ìý | Ìý | Ìý | Ìý | Ìý | 0.0 | Ìý |
| EBITDA | (2.1) | Ìý | Ìý | (1.0) | Ìý | Ìý | (4.0) | (2.5) |
| Adjusted EBITDA | (2.1) | Ìý | Ìý | (1.0) | Ìý | Ìý | (4.0) | (2.5) |
| Property, Plant and Equipment, Additions | 160.5 | Ìý | Ìý | 40.6 | Ìý | Ìý | 398.0 | 143.6 |
| Corporate and Other Segments [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| EBITDA | (32.1) | Ìý | Ìý | 215.1 | Ìý | Ìý | (98.3) | 58.0 |
| Adjusted EBITDA | (36.5) | Ìý | Ìý | (28.2) | Ìý | Ìý | (93.0) | (77.1) |
| Corporate and Other [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Depreciation, depletion and amortization | 1.4 | Ìý | Ìý | 1.4 | Ìý | Ìý | 4.2 | 4.2 |
| Property, Plant and Equipment, Additions | 2.1 | Ìý | Ìý | 0.2 | Ìý | Ìý | 3.1 | 1.1 |
| Operating Segments [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Revenues | 590.6 | Ìý | Ìý | Ìý | Ìý | Ìý | 1,494.8 | Ìý |
| SALES MARGIN | 165.8 | Ìý | Ìý | Ìý | Ìý | Ìý | 461.3 | Ìý |
| Operating Segments [Member] | Mining and Pelletizing [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Revenues | 590.6 | Ìý | Ìý | Ìý | Ìý | Ìý | 1,494.8 | Ìý |
| SALES MARGIN | 165.8 | Ìý | Ìý | Ìý | Ìý | Ìý | 461.3 | Ìý |
| Operating Segments [Member] | Metallics [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Revenues | 0.0 | Ìý | Ìý | Ìý | Ìý | Ìý | 0.0 | Ìý |
| SALES MARGIN | 0.0 | Ìý | Ìý | Ìý | Ìý | Ìý | 0.0 | Ìý |
| Intersegment Eliminations [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Revenues | (35.0) | Ìý | Ìý | Ìý | Ìý | Ìý | (39.0) | Ìý |
| SALES MARGIN | (10.9) | Ìý | Ìý | Ìý | Ìý | Ìý | (12.5) | Ìý |
| Intersegment Eliminations [Member] | Mining and Pelletizing [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Revenues | (35.0) | Ìý | Ìý | Ìý | Ìý | Ìý | (39.0) | Ìý |
| SALES MARGIN | (10.9) | Ìý | Ìý | Ìý | Ìý | Ìý | (12.5) | Ìý |
| Intersegment Eliminations [Member] | Metallics [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Revenues | 0.0 | Ìý | Ìý | Ìý | Ìý | Ìý | 0.0 | Ìý |
| SALES MARGIN | 0.0 | Ìý | Ìý | Ìý | Ìý | Ìý | 0.0 | Ìý |
| EBITDA Calculation [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Interest expense, net | (25.4) | Ìý | Ìý | (29.7) | Ìý | Ìý | (76.8) | (95.5) |
| Income tax expense | (4.8) | Ìý | Ìý | (0.5) | Ìý | Ìý | (23.1) | (14.4) |
| Depreciation, depletion and amortization | 22.2 | Ìý | Ìý | 19.2 | Ìý | Ìý | 63.1 | 68.6 |
| Adjusted EBITDA Calculation [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Segment Reporting Information [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Impact of discontinued operations | (0.8) | Ìý | Ìý | 238.2 | Ìý | Ìý | (1.2) | 120.4 |
| Gain (loss) on extinguishment of debt | 0.0 | Ìý | Ìý | 0.0 | Ìý | Ìý | (18.2) | 0.2 |
| Severance costs | 0.0 | Ìý | Ìý | 0.0 | Ìý | Ìý | (1.7) | 0.0 |
| Foreign exchange remeasurement | 0.0 | Ìý | Ìý | (0.2) | Ìý | Ìý | 0.0 | (0.7) |
| Impairment of long-lived assets | $ 0.0 | Ìý | Ìý | $ (1.1) | Ìý | Ìý | $ 0.0 | $ (1.1) |