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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 | 6 Months Ended
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Jun. 30, 2017 USD ($) MMBTU MWh gal | Jun. 30, 2016 USD ($) MMBTU MWh gal | Jun. 30, 2017 USD ($) MMBTU MWh gal | Jun. 30, 2016 USD ($) MMBTU MWh gal
Realized Gain (Loss) on Derivatives, Net |  |  |  |
Gains (Losses) | $ 3.1 | $ (19.4) | $ 5.3 | $ (51.0)
Natural gas contracts |  |  |  |
Realized Gain (Loss) on Derivatives, Net |  |  |  |
Gains (Losses) | $ 1.3 | $ (20.0) | $ 1.0 | $ (53.5)
Notional Sales Volumes |  |  |  |
Notional sales volumes | MMBTU | 25.2 | 32.7 | 59.3 | 82.8
Petroleum products contracts |  |  |  |
Realized Gain (Loss) on Derivatives, Net |  |  |  |
Gains (Losses) | $ (0.4) | $ (1.0) | $ (0.9) | $ (2.1)
Notional Sales Volumes |  |  |  |
Notional sales volumes (gallons) | gal | 4.9 | 3.6 | 9.8 | 6.6
FTRs |  |  |  |
Realized Gain (Loss) on Derivatives, Net |  |  |  |
Gains (Losses) | $ 2.2 | $ 1.6 | $ 5.2 | $ 4.6
Notional Sales Volumes |  |  |  |
Notional sales volumes | MWh | 9.4 | 7.4 | 18.6 | 15.0

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