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DISCONTINUED OPERATIONS (Narrative) (Details) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Impairment of long-lived assets |  | $ 0 | $ 0 | $ 76,600,000
Discontinued Operation, Tax Effect of Discontinued Operation |  | 0 | 0 | (6,000,000)
Deconsolidation, Gain (Loss), Amount |  |  |  | (528,200,000)
Short-term loan receivable |  | 7,700,000 |  |
LOSS FROM DISCONTINUED OPERATIONS, net of tax |  | (18,700,000) | (19,900,000) | (892,100,000)
Potential Earn Out from North American Coal sale |  | 50,000,000 |  |
Contingent claims |  | 55,600,000 | 0 |
Canadian Entities [Member] |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Impairment of long-lived assets |  |  |  | 0
Disposal Group, Including Discontinued Operation, Revenue |  | 0 | 0 | 11,300,000
Discontinued Operation, Tax Effect of Discontinued Operation |  | 0 | 0 | 5,800,000
Deconsolidation, Gain (Loss), Amount |  | (21,300,000) | (17,500,000) | (710,900,000)
Cost Method Investments |  | 0 | 0 |
Disposal Group, Including Discontinued Operation, Costs of Goods Sold |  | 0 | 0 | (11,100,000)
Disposal Group, Including Discontinued Operation, Gross Profit (Loss) |  | 0 | 0 | 200,000
Disposal Group, Including Discontinued Operation, Operating Expense |  | 0 | 0 | 33,800,000
Disposal Group, Including Discontinued Operation, Other Expense |  | 0 | 0 | (1,000,000)
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax |  | 0 | 0 | (34,600,000)
LOSS FROM DISCONTINUED OPERATIONS, net of tax |  | (21,300,000) | (17,500,000) | (739,700,000)
Loans to and Accounts Receivables from Bloom Lake Group, Fair Value Disclosure |  | 51,600,000 | 48,600,000 |
Discontinued Operations [Member] |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Impairment of long-lived assets |  |  |  | 73,400,000
North American Coal [Member] |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Impairment of long-lived assets |  |  |  | 73,400,000
Amounts released from escrow |  | 10,300,000 |  |
Disposal Group, Including Discontinued Operation, Revenue |  | 0 | 0 | 392,900,000
Discontinued Operation, Tax Effect of Discontinued Operation |  | 0 | 0 | 200,000
Tangible Asset Impairment Charges | $ 73,400,000 |  |  |
Disposal Group, Including Discontinued Operation, Costs of Goods Sold |  | 0 | 0 | (449,200,000)
Disposal Group, Including Discontinued Operation, Gross Profit (Loss) |  | 0 | 0 | (56,300,000)
Disposal Group, Including Discontinued Operation, Operating Expense |  | (500,000) | 4,500,000 | 30,400,000
Disposal Group, Including Discontinued Operation, Other Expense |  | 0 | 0 | (1,800,000)
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax |  | 2,600,000 | (2,400,000) | (79,200,000)
LOSS FROM DISCONTINUED OPERATIONS, net of tax |  | 2,600,000 | (2,400,000) | (152,400,000)
Bloom Lake Group [Member] |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Deconsolidation, Gain (Loss), Amount | $ 818,700,000 |  |  |
Contingent Liabilities recognized in Consolidated Financials |  |  | 37,200,000 |
Contingent Liabilities of Deconsolidated Entities |  | (24,300,000) | 0 | $ (203,100,000)
Wabush Group [Member] |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Deconsolidation, Gain (Loss), Amount |  |  | 134,700,000 |
Other Current Assets [Member] | Canadian Entities [Member] |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Pre-Petition Financing |  | 7,200,000 |  |
Fair Value, Inputs, Level 3 [Member] | Other Current Assets [Member] | Canadian Entities [Member] |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Loans, Associated Interest and Accounts Receivable recognized in Consolidated Financials at Fair Value |  | 51,600,000 | $ 48,600,000 |
Wabush Scully Mine Sale [Member] |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
LOSS FROM DISCONTINUED OPERATIONS, net of tax |  | $ 31,400,000 |  |

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