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Risk Management Activities and Derivative Transactions Derivatives Under Financial Trading Program (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Jun. 30, 2013 | Jun. 30, 2012 | Jun. 30, 2013 | Jun. 30, 2012 | Sep. 30, 2012
Natural Gas Futures |  |  |  |  |
Derivative |  |  |  |  |
Notional amount | 0 |  | 0 |  | 0
Fair value | $ 0 |  | $ 0 |  | $ 0
Fuel Oil and Crude Oil Futures |  |  |  |  |
Derivative |  |  |  |  |
Notional amount | 0 |  | 0 |  | 0
Fair value | 0 |  | 0 |  | 0
Coal Futures |  |  |  |  |
Derivative |  |  |  |  |
Notional amount | 0 |  | 0 |  | 0
Fair value | 0 |  | 0 |  | 0
Natural Gas Swap |  |  |  |  |
Derivative |  |  |  |  |
Notional amount | 165,662,500 |  | 165,662,500 |  | 294,462,500
Fair value | (179) |  | (179) |  | (232)
Fuel Oil and Crude Oil Swap |  |  |  |  |
Derivative |  |  |  |  |
Notional amount | 1,313,000 |  | 1,313,000 |  | 1,390,000
Fair value | (2) |  | (2) |  | 4
Coal Swap |  |  |  |  |
Derivative |  |  |  |  |
Notional amount | 0 |  | 0 |  | 0
Fair value | 0 |  | 0 |  | 0
Natural Gas Option |  |  |  |  |
Derivative |  |  |  |  |
Notional amount | 0 |  | 0 |  | 0
Fair value | 0 |  | 0 |  | 0
Fuel Oil and Crude Oil Option |  |  |  |  |
Derivative |  |  |  |  |
Notional amount | 0 |  | 0 |  | 0
Fair value | 0 |  | 0 |  | 0
Coal Option |  |  |  |  |
Derivative |  |  |  |  |
Notional amount | 0 |  | 0 |  | 0
Fair value | 0 |  | 0 |  | 0
Natural Gas Total Contracts |  |  |  |  |
Derivative |  |  |  |  |
Notional amount | 165,662,500 |  | 165,662,500 |  | 294,462,500
Fair value | (179) |  | (179) |  | (232)
Decrease (increase) in fuel expense | (13) | (53) | (60) | (69) |
Decrease (increase) in purchased power expense | (8) | (53) | (40) | (189) |
Fuel Oil and Crude Oil Total Contracts |  |  |  |  |
Derivative |  |  |  |  |
Notional amount | 1,313,000 |  | 1,313,000 |  | 1,390,000
Fair value | (2) |  | (2) |  | 4
Decrease (increase) in fuel expense | 0 | 1 | 2 | 9 |
Coal Contract Total Contracts |  |  |  |  |
Derivative |  |  |  |  |
Notional amount | 0 |  | 0 |  | 0
Fair value | 0 |  | 0 |  | 0
Decrease (increase) in fuel expense | 0 | 0 | (1) | 1 |
Closed derivative contracts |  |  |  |  |
Derivative |  |  |  |  |
Fair value | $ (9) |  | $ (9) |  | $ (21)

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 + 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 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=28364263&loc=d3e13433-108611 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 15 -URI http://asc.fasb.org/extlink&oid=28364263&loc=d3e13495-108611 Reference 4: 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 + Details
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