XML 96 R62.htm IDEA: XBRL DOCUMENT
v3.19.1

Risk Management Activities and Derivative Transactions Derivatives Under FTP (Details) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Mar. 31, 2019 USD ($) | Mar. 31, 2018 USD ($) | Mar. 31, 2019 USD ($) | Mar. 31, 2018 USD ($) | Sep. 30, 2018 USD ($)
Derivative |  |  |  |  |
Forward Contract Derivative Asset, at Fair Value | $ 59 |  | $ 59 |  | $ 45
Coal Contract |  |  |  |  |
Derivative |  |  |  |  |
Notional amount | 15,000,000 |  | 15,000,000 |  | 20,000,000
Fair value | $ 38 |  | $ 38 |  | $ 58
Natural Gas Contract Derivatives |  |  |  |  |
Derivative |  |  |  |  |
Notional amount | 360,000,000 |  | 360,000,000 |  | 359,000,000
Fair value | $ (10) |  | $ (10) |  | $ 2
Natural Gas Contract Derivatives |  |  |  |  |
Derivative |  |  |  |  |
Decrease (increase) in fuel expense | 0 | $ 0 | 0 | $ (6) |
Decrease (increase) in purchased power expense | 0 | $ 0 | 0 | $ (2) |
Fair Value, Inputs, Level 2 |  |  |  |  |
Derivative |  |  |  |  |
Forward Contract Derivative Asset, at Fair Value | $ 59 |  | $ 59 |  | $ 45

X
- Definition Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
Name: | invest_DerivativeNonmonetaryNotionalAmount
Namespace Prefix: | invest_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition The decrease (increase) in fuel expense relating to the FTP. + References No definition available. + Details
Name: | tve_DecreaseIncreaseInFuelExpense
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

X
- Definition The decrease (increase) in purchased power expense related to the FTP. + References No definition available. + Details
Name: | tve_DecreaseIncreaseInPurchasedPowerExpense
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fair value as of the balance sheet date of forward contract derivative assets. + References No definition available. + Details
Name: | tve_ForwardContractDerivativeAssetatFairValue
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Fair value of the assets less the liabilities of a derivative or group of derivatives. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611 + Details
Name: | us-gaap_DerivativeFairValueOfDerivativeNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=us-gaap_CoalContractMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=srt_NaturalGasReservesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | tve_DerivativesUnderFinancialTradingProgramAxis=srt_NaturalGasReservesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |