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v3.23.2

Summary of Significant Accounting Policies Revenues (Details) $ in Millions | 9 Months Ended
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Jun. 30, 2023 USD ($) Item
Accounting Policies [Abstract] |
Number of customers with billing dates before month end | Item | 5
Property, Plant and Equipment [Line Items] |
Pre-commercial Ops - capitalized revenue | $ 1
Pre-commercial Ops - Capitalized Fuel | $ 1

X
- Definition Number of customers with billing dates before month end + References No definition available. + Details
Name: | tve_NumberOfCustomersWithBillingDatesBeforeMonthEnd
Namespace Prefix: | tve_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Pre-commercial Ops - Capitalized Fuel + References No definition available. + Details
Name: | tve_PreCommercialOpsCapitalizedFuel
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Pre-commercial Ops - capitalized revenue + References No definition available. + Details
Name: | tve_PreCommercialOpsCapitalizedRevenue
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_AccountingPoliciesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_PropertyPlantAndEquipmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration