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DERIVATIVE INSTRUMENTS - VOLUME (Details) certificate in Thousands, $ in Millions	Sep. 30, 2017 USD ($) Bcf certificate	Sep. 30, 2016 Bcf	Jun. 01, 2015 USD ($)
Derivative [Line Items]
Derivative, notional amount | $			$ 125.0
Foreign currency contracts
Derivative [Line Items]
Derivative, notional amount | $	$ 4.5
Energy Services | Physical commodity contracts
Derivative [Line Items]
Number of Solar Renewable Energy Certificates (in certificates) | certificate	283
Long | Natural Gas Distribution | Futures
Derivative [Line Items]
Outstanding long (short) derivatives (in Bcf)	18.2	23.6
Long | Natural Gas Distribution | Physical
Derivative [Line Items]
Outstanding long (short) derivatives (in Bcf)	32.1	9.2
Long | Energy Services | Physical
Derivative [Line Items]
Outstanding long (short) derivatives (in Bcf)		94.6
Long | Energy Services | Financial Options
Derivative [Line Items]
Outstanding long (short) derivatives (in Bcf)	0.0	1.2
Short | Energy Services | Futures
Derivative [Line Items]
Outstanding long (short) derivatives (in Bcf)	16.4	79.1
Short | Energy Services | Physical
Derivative [Line Items]
Outstanding long (short) derivatives (in Bcf)	13.1

X

- Definition

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
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