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DERIVATIVE INSTRUMENTS - VOLUME (Details) $ in Millions | Sep. 30, 2018 USD ($) Bcf certificate | Sep. 30, 2017 Bcf
--- | --- | ---
Foreign currency contracts |  |
Derivative [Line Items] |  |
Derivative, notional amount | $ | $ 8.5 |
Natural Gas Distribution | Long | Futures |  |
Derivative [Line Items] |  |
Outstanding long (short) derivatives (in Bcf) | 27.9 | 18.2
Natural Gas Distribution | Long | Physical |  |
Derivative [Line Items] |  |
Outstanding long (short) derivatives (in Bcf) | 23.1 | 32.1
Energy Services | Physical commodity contracts |  |
Derivative [Line Items] |  |
Number of Solar Renewable Energy Certificates (in certificates) | certificate | (698,700) |
Energy Services | Short | Futures |  |
Derivative [Line Items] |  |
Outstanding long (short) derivatives (in Bcf) | (7.0) | (16.4)
Energy Services | Short | Physical |  |
Derivative [Line Items] |  |
Outstanding long (short) derivatives (in Bcf) | 51.2 | (13.1)

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