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v3.23.3

Summary of Significant Accounting Policies - Pre-commercial Plant Ops (Details) - USD ($) $ in Millions | 12 Months Ended
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Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021
Revenues from External Customers and Long-Lived Assets [Line Items] |  |  |
Revenue capitalized during pre-commercial operations | $ 3 | $ 0 | $ 0
Fuel capitalized during pre-commercial ops | $ 3 |  |

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- Definition Fuel capitalized during pre-commercial ops + References No definition available. + Details
Name: | tve_FuelCapitalizedDuringPreCommercialOps
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Revenue capitalized during pre-commercial operations + References No definition available. + Details
Name: | tve_RevenueCapitalizedDuringPreCommercialOperations
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- 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_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration