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v3.19.3

Subsequent Events Subsequent Events (Details) $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2019 USD ($)
Debt Instrument, Redemption [Line Items] |
Amount of bonds redeemed | $ 217

X
- Definition The amount of bonds redeemed. + References No definition available. + Details
Name: | tve_AmountOfBondsRedeemed
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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_DebtInstrumentRedemptionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration