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Risk Management Activities and Derivative Transactions Risk Management Activities and Derivative Transactions - Counterparty Credit Risk (Details) | 12 Months Ended
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Sep. 30, 2013 Customers | Sep. 30, 2012 Customers
Derivative |  |
Number of active future commission merchants | 2 |
Credit of Customers |  |
Derivative |  |
Number of customers that represent the percent of outstanding accounts receivable | 3 | 3
Percent of total outstanding accounts receivables by customers | 27.00% | 26.00%
Percent of operating revenue represented by largest industrial customer | 3.00% | 5.00%
Power Purchase Agreement |  |
Derivative |  |
Megawatts in a power purchase agreement that expires on March 31, 2032 | 440 |

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- Definition Number of active future commission merchants to clear commodity contracts. + References No definition available. + Details
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- Definition The percent of total outstanding accounts receivables represented by a certain number of customers. + References No definition available. + Details
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