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v3.20.2

Leases, SoCF (Details) $ in Millions | 12 Months Ended
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Sep. 30, 2020 USD ($)
Lessee, Lease, Description [Line Items] |
Operating cash flows for operating leases | $ 85
Operating cash flows for finance leases | 33
Financing cash flows for finance leases | 15
Lease assets obtained in exchange for lease obligations - finance | 394
Lease assets obtained in exchange for lease obligations - operating | $ 110

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- Definition Financing cash flows for finance leases + References No definition available. + Details
Name: | tve_FinancingCashFlowsForFinanceLeases
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Lease assets obtained in exchange for lease obligations - finance + References No definition available. + Details
Name: | tve_LeaseAssetsObtainedInExchangeForLeaseObligationsFinance
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Lease assets obtained in exchange for lease obligations - operating + References No definition available. + Details
Name: | tve_LeaseAssetsObtainedInExchangeForLeaseObligationsOperating
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Operating cash flows for finance leases + References No definition available. + Details
Name: | tve_OperatingCashFlowsForFinanceLeases
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Operating cash flows for operating leases + References No definition available. + Details
Name: | tve_OperatingCashFlowsForOperatingLeases
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_LesseeLeaseDescriptionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration