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Revenue Energy Prepayment Obligations (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2004
Energy Prepayment Obligation [Line Items] |  |  |  |
Electric revenue | $ 10,104 | $ 11,159 | $ 11,075 |
Energy Prepayment Discount | $ 4 | $ 46 |  |
MLGW |  |  |  |
Energy Prepayment Obligation [Line Items] |  |  |  |
Deferred Revenue, Description | 10 million | 100 million |  | 100 million

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- Definition Revenue from sales of electricity + References No definition available. + Details
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Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Energy Prepayment Discount + References No definition available. + Details
Name: | tve_EnergyPrepaymentDiscount
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition [Line Items] for Energy Prepayment Obligation [Table] + References No definition available. + Details
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- Definition Description of the transaction or nature of business giving rise to deferred revenue or unearned revenue, other than annual membership fees. Deferred revenue is a liability related to a revenue producing activity for which revenue has not yet been recognized. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP. + References Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 8 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121566466&loc=d3e6935-107765 + Details
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- Details
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