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DERIVATIVE INSTRUMENTS (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |  |
--- | --- | --- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Jan. 01, 2018 | Dec. 31, 2017
Derivative [Line Items] |  |  |  |  |  |
Natural Gas Hedges | $ 3.4 |  | $ 3.4 |  |  | $ 3.5
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax | (0.2) |  | (0.6) |  |  |
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net |  |  | 0.1 |  |  |
Derivative assets | 174.7 |  | 174.7 |  | $ 49.5 | 37.9
Derivative Liability | 3.1 |  | 3.1 |  |  | 2.0
Not Designated as Hedging Instrument [Member] |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |
Derivative assets | 174.6 |  | 174.6 |  |  | 37.9
Derivative Liability | 3.0 |  | 3.0 |  |  | 1.7
Customer Supply Agreement [Member] | Not Designated as Hedging Instrument [Member] | Product Revenues [Member] |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |
Amount of gain/(loss) recognized in income on derivative | (155.5) | $ (51.9) | (197.4) | $ (69.6) |  |
Customer Supply Agreement [Member] | Not Designated as Hedging Instrument [Member] | Derivative Financial Instruments, Assets [Member] |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |
Derivative assets | 169.4 |  | 169.4 |  |  | 37.9
Provisional Pricing Arrangements [Member] | Not Designated as Hedging Instrument [Member] | Product Revenues [Member] |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |
Amount of gain/(loss) recognized in income on derivative | 0.8 | $ 21.1 | (1.1) | $ 5.3 |  |
Provisional Pricing Arrangements [Member] | Not Designated as Hedging Instrument [Member] | Derivative Financial Instruments, Assets [Member] |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |
Derivative assets | $ 5.2 |  | $ 5.2 |  |  | $ 0.0

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- Definition Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13495-108611 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611 + Details
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