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DISCONTINUED OPERATIONS Discontinued Operations, Items Measured at Fair Value on a Non-Recurring Basis - North American Coal (Details) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2016 | Mar. 31, 2015 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Discontinued Operations, Items Measured at Fair Value on a Non-Recurring Basis [Line Items] |  |  |  |  |
Tangible Asset Impairment Charges |  |  | $ 0 | $ 0 | $ 537,800,000
North American Coal [Member] |  |  |  |  |
Discontinued Operations, Items Measured at Fair Value on a Non-Recurring Basis [Line Items] |  |  |  |  |
Property, Plant, and Equipment, Fair Value Disclosure |  | $ 20,400,000 |  |  |
Tangible Asset Impairment Charges |  | 73,400,000 |  |  |
Assets, Fair Value Disclosure, Nonrecurring |  | 20,400,000 |  |  |
Impairment Charges | $ 73,400,000 |  |  |  |
Fair Value, Inputs, Level 1 [Member] | North American Coal [Member] |  |  |  |  |
Discontinued Operations, Items Measured at Fair Value on a Non-Recurring Basis [Line Items] |  |  |  |  |
Property, Plant, and Equipment, Fair Value Disclosure |  | 0 |  |  |
Assets, Fair Value Disclosure, Nonrecurring |  | 0 |  |  |
Fair Value, Inputs, Level 2 [Member] | North American Coal [Member] |  |  |  |  |
Discontinued Operations, Items Measured at Fair Value on a Non-Recurring Basis [Line Items] |  |  |  |  |
Property, Plant, and Equipment, Fair Value Disclosure |  | 0 |  |  |
Assets, Fair Value Disclosure, Nonrecurring |  | 0 |  |  |
Fair Value, Inputs, Level 3 [Member] | North American Coal [Member] |  |  |  |  |
Discontinued Operations, Items Measured at Fair Value on a Non-Recurring Basis [Line Items] |  |  |  |  |
Property, Plant, and Equipment, Fair Value Disclosure |  | 20,400,000 |  |  |
Assets, Fair Value Disclosure, Nonrecurring |  | $ 20,400,000 |  |  |

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- Definition [Line Items] for Discontinued Operations, Items Measured at Fair Value on a Non-Recurring Basis [Table] + References No definition available. + Details
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- Definition This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a nonrecurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. + References No definition available. + Details
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- Definition Fair value portion of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19190-110258 + Details
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- Definition The charge against earnings resulting from the aggregate write down of tangible assets from their carrying value to their fair value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=64862545&loc=d3e2921-110230 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=64827811&loc=d3e1361-107760 + Details
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