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v3.20.1

Summary of Significant Accounting Policies Leases (Details) | 6 Months Ended
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Mar. 31, 2020
Lease obligation related to Purchased Power [Line Items] |
Lease obligation related to Purchased Power [Table Text Block] | 296

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- Definition [Line Items] for Lease obligation related to Purchased Power + References No definition available. + Details
Name: | tve_LeaseobligationrelatedtoPurchasedPowerLineItems
Namespace Prefix: | tve_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition [Table Text Block] for Lease obligation related to Purchased Power + References No definition available. + Details
Name: | tve_LeaseobligationrelatedtoPurchasedPowerTableTextBlock
Namespace Prefix: | tve_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration