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Risk Management Activities and Derivative Transactions Risk Management Activities and Derivative Transactions - Derivatives Under Financial Trading Program (Details) $ in Millions | 12 Months Ended
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Sep. 30, 2018 USD ($) | Sep. 30, 2017 USD ($)
Derivative |  |
FTP transaction limit | $ 130 |
Natural Gas Swap |  |
Derivative |  |
Notional amount | 0 | 2,800,000
Unrealized gains (losses) deferred as regulatory liabilities (assets) | $ 0 | $ (5)
Natural Gas Contract Derivatives |  |
Derivative |  |
Unrealized gains (losses) deferred as regulatory liabilities (assets) | 0 | (5)
Decrease (increase) in fuel expense | (6) | (29)
Decrease (increase) in purchased power expense | $ (2) | (7)
Closed Derivative Contracts |  |
Derivative |  |
Unrealized gains (losses) deferred as regulatory liabilities (assets) |  | $ (3)

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- 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 + Details
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- Definition The decrease (increase) in fuel expense relating to the FTP. + References No definition available. + Details
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- Definition The decrease (increase) in purchased power expense related to the FTP. + References No definition available. + Details
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- Definition FTP transaction limit + References No definition available. + Details
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- Definition Fair value of the assets less the liabilities of a derivative or group of derivatives. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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- Details
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- Details
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