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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		9 Months Ended
	Sep. 30, 2019 USD ($) MMBTU MWh gal	Sep. 30, 2018 USD ($) MMBTU MWh gal	Sep. 30, 2019 USD ($) MMBTU MWh gal	Sep. 30, 2018 USD ($) MMBTU MWh gal
Realized gains (losses)
Gains (losses)	$ (5.6)	$ 8.0	$ (3.9)	$ 8.9
Natural gas contracts
Realized gains (losses)
Gains (losses)	$ (13.2)	$ 0.4	$ (16.8)	$ (7.1)
Notional sales volumes
Notional sales volumes | MMBTU	37.8	36.7	137.7	124.7
Petroleum products contracts
Realized gains (losses)
Gains (losses)	$ 0.0	$ 0.5	$ 0.0	$ 1.3
Notional sales volumes
Notional sales volumes (gallons) | gal	0.0	1.3	0.0	5.1
FTRs
Realized gains (losses)
Gains (losses)	$ 7.6	$ 7.1	$ 12.9	$ 14.7
Notional sales volumes
Notional sales volumes | MWh	7.8	7.9	23.9	22.9

X

- Definition

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959

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- Definition

Nominal energy measure used to calculate payments on a derivative instrument.

+ References

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- Definition

Nominal volume used to calculate payments on a derivative instrument.

+ References

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