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v2.4.1.9

Risk Management Activities and Derivative Transactions Counterparty Credit Risk (Details) | Mar. 31, 2015 Customers | Sep. 30, 2014 Customers
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Derivative |  |
Number of active future commission merchants | 2 tve_NumberOfActiveFutureCommissionMerchants |
Megawatts | 700 tve_Megawatts |
Credit of Customers [Member] |  |
Derivative |  |
Number of customers that represent the concentration of accounts receivable percent outstanding | 3 tve_NumberOfCustomersThatRepresentPercentOfOutstandingAccountsReceivable / us-gaap_DerivativeByNatureAxis = tve_CreditOfCustomersMember | 3 tve_NumberOfCustomersThatRepresentPercentOfOutstandingAccountsReceivable / us-gaap_DerivativeByNatureAxis = tve_CreditOfCustomersMember
Percent of total outstanding accounts receivables | 24.00%tve_PercentOfTotalOutstandingAccountsReceivables / us-gaap_DerivativeByNatureAxis = tve_CreditOfCustomersMember | 27.00%tve_PercentOfTotalOutstandingAccountsReceivables / us-gaap_DerivativeByNatureAxis = tve_CreditOfCustomersMember
Power Purchase Agreement |  |
Derivative |  |
Megawatts | 440 tve_Megawatts / us-gaap_DerivativeByNatureAxis = us-gaap_LongTermContractForPurchaseOfElectricPowerDomain |

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- 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

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- Definition Number of active future commission merchants to clear commodity contracts. + References No definition available. + Details
Name: | tve_NumberOfActiveFutureCommissionMerchants
Namespace Prefix: | tve_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- 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

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- 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

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

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- Details
Name: | us-gaap_DerivativeByNatureAxis=tve_CreditOfCustomersMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_DerivativeByNatureAxis=us-gaap_LongTermContractForPurchaseOfElectricPowerDomain
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |