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Risk Management Activities and Derivative Transactions Counterparty Credit Risk (Details) | Dec. 31, 2013 | Sep. 30, 2013 Customers
--- | --- | ---
Credit of Customers [Member] |  |
Derivative |  |
Number of customers that represent the percent of outstanding accounts receivable | 3 | 3
Percent of total outstanding accounts receivables | 23.00% | 26.00%
Power Purchase Agreement |  |
Derivative |  |
Megawatts | 440 |

X
- Definition Megawatts of summer net capability + References No definition available. + Details
Name: | tve_Megawatts
Namespace Prefix: | tve_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The number of customers that represent the percent of outstanding accounts receivable. + References No definition available. + Details
Name: | tve_NumberOfCustomersThatRepresentPercentOfOutstandingAccountsReceivable
Namespace Prefix: | tve_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The percent of total outstanding accounts receivables represented by a certain number of customers. + References No definition available. + Details
Name: | tve_PercentOfTotalOutstandingAccountsReceivables
Namespace Prefix: | tve_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_DerivativeLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration