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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
--- | ---
Sep. 30, 2016 USD ($) | Sep. 30, 2015 USD ($)
Derivative |  |
FTP transaction limit | $ 130 |
Natural Gas Swap |  |
Derivative |  |
Notional amount | 21,052,500 | 51,495,000
Unrealized gains (losses) deferred as regulatory liabilities (assets) | $ (39) | $ (116)
Natural Gas Contract Derivatives |  |
Derivative |  |
Unrealized gains (losses) deferred as regulatory liabilities (assets) | (39) | (116)
Decrease (increase) in fuel expense | (75) | (79)
Decrease (increase) in purchased power expense | (19) | (20)
Fuel oil/crude oil |  |
Derivative |  |
Decrease (increase) in fuel expense | 0 | 1
Closed Derivative Contracts |  |
Derivative |  |
Unrealized gains (losses) deferred as regulatory liabilities (assets) | $ (5) | $ (11)
Swap contracts |  |
Derivative |  |
Remaining terms | 2 |

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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 Fair value of the assets less the liabilities of a derivative or group of derivatives. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13433-108611 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13495-108611 + Details
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- Details
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