EARNINGS PER SHARE (Earnings Per Share Computation) (Details) - USD ($) |
3 Months Ended | 12 Months Ended | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2018 |
Sep. 30, 2018 |
Jun. 30, 2018 |
Mar. 31, 2018 |
Dec. 31, 2017 |
Sep. 30, 2017 |
Jun. 30, 2017 |
Mar. 31, 2017 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Debt Instrument [Line Items] | |||||||||||
| INCOME FROM CONTINUING OPERATIONS | $ 333,000,000 | $ 22,300,000 | $ 83,800,000 | $ (78,500,000) | $ 1,039,900,000 | $ 360,600,000 | $ 122,600,000 | ||||
| Net Income (Loss) Attributable to Noncontrolling Interest | 0 | (3,900,000) | 25,200,000 | ||||||||
| Income (Loss) from Continuing Operations, Net of Tax, Attributable to Noncontrolling Interest | 0 | 500,000 | 1,700,000 | 1,700,000 | |||||||
| Income (Loss) from Continuing Operations Attributable to Parent | $ 624,100,000 | $ 199,800,000 | $ 229,400,000 | $ (13,400,000) | 333,000,000 | 22,800,000 | 85,500,000 | (76,800,000) | 1,039,900,000 | 364,500,000 | 97,400,000 |
| INCOME FROM DISCONTINUED OPERATIONS, net of tax | 88,200,000 | 2,500,000 | 76,700,000 | ||||||||
| INCOME FROM DISCONTINUED OPERATIONS, net of tax | (14,600,000) | 238,000,000 | (64,300,000) | (70,900,000) | (23,100,000) | 30,600,000 | (53,700,000) | 48,700,000 | 88,200,000 | 2,500,000 | 76,700,000 |
| Net income attributable to Cliffs shareholders | $ 609,500,000 | $ 437,800,000 | $ 165,100,000 | $ (84,300,000) | $ 309,900,000 | $ 53,400,000 | $ 31,800,000 | $ (28,100,000) | $ 1,128,100,000 | $ 367,000,000 | $ 174,100,000 |
| Weighted average number of shares: | |||||||||||
| Basic | 297,200,000 | 288,400,000 | 197,700,000 | ||||||||
| $316.5 million 1.50% 2025 Convertible Senior Notes | 3,400,000 | 0 | 0 | ||||||||
| Employee stock plans | 3,500,000 | 4,600,000 | 2,400,000 | ||||||||
| Diluted | 304,100,000 | 293,000,000 | 200,100,000 | ||||||||
| Earnings per common share attributable to Cliffs common shareholders - basic: | |||||||||||
| Continuing operations | $ 2.11 | $ 0.67 | $ 0.77 | $ (0.05) | $ 1.12 | $ 0.08 | $ 0.28 | $ (0.29) | $ 3.50 | $ 1.27 | $ 0.49 |
| Discontinued operations | (0.05) | 0.80 | (0.22) | (0.24) | (0.08) | 0.10 | (0.18) | 0.18 | 0.30 | 0.01 | 0.39 |
| Earnings per common share attributable to Cliffs common shareholders - basic: | 2.06 | 1.47 | 0.55 | (0.29) | 1.04 | 0.18 | 0.10 | (0.11) | 3.80 | 1.28 | 0.88 |
| Earnings per common share attributable to Cliffs common shareholders - diluted: | |||||||||||
| Continuing operations | 2.03 | 0.64 | 0.76 | (0.05) | 1.11 | 0.08 | 0.28 | (0.29) | 3.42 | 1.25 | 0.49 |
| Discontinued operations | (0.05) | 0.77 | (0.21) | (0.24) | (0.08) | 0.10 | (0.18) | 0.18 | 0.29 | 0.01 | 0.38 |
| Earnings per common share attributable to Cliffs common shareholders - diluted: | $ 1.98 | $ 1.41 | $ 0.55 | $ (0.29) | $ 1.03 | $ 0.18 | $ 0.10 | $ (0.11) | $ 3.71 | $ 1.26 | $ 0.87 |
| Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | 3,800,000.0 | 4,600,000.0 | 0 | ||||||||
| $316 Million 1.5% 2025 Senior Notes [Domain] | |||||||||||
| Debt Instrument [Line Items] | |||||||||||
| Face amount | $ 316,250,000.00 | $ 316,250,000.00 | |||||||||
| Debt Instrument, Interest Rate, Stated Percentage | 1.50% | 1.50% | |||||||||
| X | ||||||||||
- Definition Incremental Common Shares Attributable to Convertible Shares No definition available.
|
| X | ||||||||||
- Definition Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Face (par) amount of debt instrument at time of issuance. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Contractual interest rate for funds borrowed, under the debt agreement. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| 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 | ||||||||||
- Definition The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
|
| X | ||||||||||
- References No definition available.
|
| X | ||||||||||
- Definition The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period. Reference 1: http://www.xbrl.org/2003/role/exampleRef
|
| X | ||||||||||
- References No definition available.
|
| X | ||||||||||
- Definition Amount after tax of income (loss) from continuing operations attributable to the parent. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount after tax of income (loss) from continuing operations attributable to the noncontrolling interest. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount after tax of income (loss) from continuing operations including portion attributable to the noncontrolling interest. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition The amount of net income (loss) from continuing operations per each share of common stock or unit outstanding during the reporting period. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition The amount of net income (loss) derived from continuing operations during the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount after tax of income (loss) from a discontinued operation including the portion attributable to the noncontrolling interest. Includes, but is not limited to, the income (loss) from operations during the phase-out period, gain (loss) on disposal, gain (loss) for reversal of write-down (write-down) to fair value, less cost to sell, and adjustments to a prior period gain (loss) on disposal. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount after tax of income (loss) from a discontinued operation attributable to the parent. Includes, but is not limited to, the income (loss) from operations during the phase-out period, gain (loss) on disposal, gain (loss) for reversal of write-down (write-down) to fair value, less cost to sell, and adjustments to a prior period gain (loss) on disposal. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Per basic share amount, after tax, of income (loss) from the day-to-day business activities of the discontinued operation and gain (loss) from the disposal of the discontinued operation. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
|
| X | ||||||||||
- Definition Per diluted share amount, after tax, of income (loss) from the day-to-day business activities of the discontinued operation and gain (loss) from the disposal of the discontinued operation. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
|
| X | ||||||||||
- Definition Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition The portion of profit or loss for the period, net of income taxes, which is attributable to the parent. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
|
| X | ||||||||||
- Definition Amount of Net Income (Loss) attributable to noncontrolling interest. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
|
| X | ||||||||||
- Definition The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- References No definition available.
|
| X | ||||||||||
- Definition Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Details
|