BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details) T in Millions, $ in Millions |
3 Months Ended | 12 Months Ended | |||||||||||
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Dec. 31, 2019
USD ($)
T
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Sep. 30, 2019
USD ($)
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Jun. 30, 2019
USD ($)
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Mar. 31, 2019
USD ($)
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Dec. 31, 2018
USD ($)
T
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Sep. 30, 2018
USD ($)
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Jun. 30, 2018
USD ($)
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Mar. 31, 2018
USD ($)
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Dec. 31, 2019
USD ($)
unit
T
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Dec. 31, 2018
USD ($)
T
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Dec. 31, 2017
USD ($)
T
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Jan. 01, 2018
USD ($)
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Dec. 31, 2016
USD ($)
|
|
Related Party Transaction [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest | $ 357.9 | Ìý | Ìý | Ìý | $ 424.2 | Ìý | Ìý | Ìý | $ 357.9 | $ 424.2 | $ (444.1) | Ìý | $ (1,330.5) |
Number of Reporting Units | unit | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 2 | Ìý | Ìý | Ìý | Ìý |
Noncontrolling Interest, Ownership Percentage by Parent | 100.00% | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 100.00% | Ìý | Ìý | Ìý | Ìý |
Net Income (Loss) Attributable to Noncontrolling Interest | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | $ 0.0 | 0.0 | (3.9) | Ìý | Ìý |
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net from product sales and services | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 7.5 | 422.6 | 119.3 | Ìý | Ìý |
Foreign Currency Transaction Gain (Loss), Realized | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 0.0 | 228.1 | 0.0 | Ìý | Ìý |
Revenues | $ 534.1 | $ 555.6 | $ 743.2 | $ 157.0 | $ 696.3 | $ 741.8 | $ 714.3 | $ 180.0 | 1,989.9 | 2,332.4 | 1,866.0 | Ìý | Ìý |
Net income | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | $ 292.8 | $ 1,128.1 | $ 363.1 | Ìý | Ìý |
Hibbing [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Related Party Transaction [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Ownership interest, equity method investment | 23.00% | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 23.00% | Ìý | Ìý | Ìý | Ìý |
Mining and Pelletizing [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Related Party Transaction [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Quantity Of Finished Goods at ports | T | 1.0 | Ìý | Ìý | Ìý | 0.8 | Ìý | Ìý | Ìý | 1.0 | 0.8 | 1.5 | Ìý | Ìý |
Revenues | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | $ 1,989.9 | $ 2,332.4 | $ 1,866.0 | Ìý | Ìý |
Empire [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Related Party Transaction [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Distribution of Noncontrolling Interest | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 132.7 | Ìý | Ìý |
Stockholders' Equity, Period Increase (Decrease) | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | (12.1) | Ìý | Ìý |
Net Income (Loss) Attributable to Noncontrolling Interest | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | (3.9) | Ìý | Ìý |
Acquisition of Noncontrolling Interest | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | (116.7) | Ìý | Ìý |
Tilden [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Related Party Transaction [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Distribution of Noncontrolling Interest | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 105.0 | Ìý | Ìý |
Stockholders' Equity, Period Increase (Decrease) | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | (89.1) | Ìý | Ìý |
Acquisition of Noncontrolling Interest | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | $ (15.9) | Ìý | Ìý |
Other Noncurrent Liabilities [Member] | Hibbing [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Related Party Transaction [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Equity Method Investments | $ (18.0) | Ìý | Ìý | Ìý | $ (15.4) | Ìý | Ìý | Ìý | $ (18.0) | (15.4) | Ìý | Ìý | Ìý |
Other Current Liabilities [Member] | Empire [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Related Party Transaction [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Noncontrolling Interest Purchase, Installment Amount | Ìý | Ìý | Ìý | Ìý | $ 44.2 | Ìý | Ìý | Ìý | Ìý | 44.2 | Ìý | Ìý | Ìý |
Tilden [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Related Party Transaction [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Noncontrolling Interest, Ownership Percentage by Parent | 100.00% | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 100.00% | Ìý | Ìý | Ìý | Ìý |
Increase in Ownership Equity | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 15.00% | Ìý | Ìý |
Empire [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Related Party Transaction [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Noncontrolling Interest, Ownership Percentage by Parent | 100.00% | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 100.00% | Ìý | Ìý | Ìý | Ìý |
Increase in Ownership Equity | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 21.00% | Ìý | Ìý |
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Related Party Transaction [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | $ 34.0 | Ìý |
Revenues | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 68.1 | Ìý | Ìý | Ìý |
Net income | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | $ 46.2 | Ìý | Ìý | Ìý |
Sales [Member] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Related Party Transaction [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net from product sales and services | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | $ 120.6 | Ìý | Ìý |
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- Definition Increase in Ownership Equity No definition available.
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- Definition Noncontrolling Interest Purchase, Installment Amount No definition available.
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- Definition Purchase of Noncontrolling Interest No definition available.
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- Definition The quantity of finished goods stored at ports and customer facilities No definition available.
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- Definition Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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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 This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Amount before tax of foreign currency transaction realized gain (loss) recognized in the income statement. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Decrease in noncontrolling interest (for example, but not limited to, redeeming or purchasing the interests of noncontrolling shareholders, issuance of shares (interests) by the non-wholly owned subsidiary to the parent entity for other than cash, and a buyback of shares (interest) by the non-wholly owned subsidiary from the noncontrolling interests). 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 Amount of Net Income (Loss) attributable to noncontrolling interest. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Number of reporting units tested for impairment of goodwill. A reporting unit is an operating segment or one level below an operating segment. No definition available.
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- Definition The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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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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- Definition Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss). Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition The increase (decrease) in stockholders' equity during the period. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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