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DERIVATIVE INSTRUMENTS - GAINS (LOSSES) AND NOTIONAL VOLUMES (Details) gal in Millions, MWh in Millions, MMBTU in Millions, $ in Millions | 3 Months Ended
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Mar. 31, 2018 USD ($) MMBTU MWh gal | Mar. 31, 2017 USD ($) MMBTU MWh gal
Realized Gain (Loss) on Derivatives, Net |  |
Gains (Losses) | $ (1.0) | $ 2.2
Natural gas contracts |  |
Realized Gain (Loss) on Derivatives, Net |  |
Gains (Losses) | $ (5.2) | $ (0.3)
Notional Sales Volumes |  |
Notional sales volumes | MMBTU | 48.1 | 34.1
Petroleum products contracts |  |
Realized Gain (Loss) on Derivatives, Net |  |
Gains (Losses) | $ 0.5 | $ (0.5)
Notional Sales Volumes |  |
Notional sales volumes (gallons) | gal | 2.1 | 4.9
FTRs |  |
Realized Gain (Loss) on Derivatives, Net |  |
Gains (Losses) | $ 3.7 | $ 3.0
Notional Sales Volumes |  |
Notional sales volumes | MWh | 8.2 | 9.2

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- Definition Amount of increase (decrease) in the fair value of derivatives recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5618551-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (a),(c),(d),(e) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959 + Details
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