XML 145 R89.htm IDEA: XBRL DOCUMENT
v3.25.3

Risk Management Activities and Derivative Transactions Risk Management Activities and Derivative Transactions - Derivative Instruments That Do Not Receive Hedge Accounting Treatment (Details) | 12 Months Ended
--- | ---
Sep. 30, 2025 USD ($) | Sep. 30, 2024 USD ($)
Derivative |  |
Change in Unrealized gains (losses) on Interest Rate Derivatives | $ (145,000,000) | $ (182,000,000)
Fair value | 12,000,000 | 64,000,000
Interest rate swaps | 698,000,000 | 840,000,000
Interest Rate Swap |  |
Derivative |  |
Unrealized gains/losses on derivatives | 45,000,000 | $ (31,000,000)
Unrealized gains/losses on derivatives | $ 0 |
Commodity Contract Derivatives |  |
Derivative |  |
Number of contracts | 53 | 45
Notional amount | 562,000,000 | 321,000,000
Fair value | $ 10,000,000 | $ 2,000,000
Commodity Contract under FHP |  |
Derivative |  |
Unrealized gains/losses on derivatives | $ (93,000,000) | $ (295,000,000)
Number of contracts | 295 | 126
Notional amount | 300 | 230
Fair value | $ (57,000,000) | $ (161,000,000)
Commodity Contract under FHP | Fuel Expense |  |
Derivative |  |
Unrealized gains/losses on derivatives | 77,000,000 | 245,000,000
Commodity Contract under FHP | Purchased Power Expense |  |
Derivative |  |
Unrealized gains/losses on derivatives | 16,000,000 | 50,000,000
Accounts payable and accrued liabilities | Commodity Contract Derivatives |  |
Derivative |  |
Fair value | (2,000,000) | (3,000,000)
Accounts payable and accrued liabilities | Commodity Contract under FHP |  |
Derivative |  |
Fair value | $ (57,000,000) | $ (99,000,000)

X
- Definition The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of interest rate derivatives held at each balance sheet date. + References No definition available. + Details
Name: | tve_ChangeinUnrealizedgainslossesonInterestRateDerivatives
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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 -Topic 825 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 10 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482907/825-10-50-10 + Details
Name: | us-gaap_DerivativeFairValueOfDerivativeNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 182 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480401/815-10-55-182 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 4CC -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-4CC Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 220 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 21 -Subparagraph (i) -Publisher FASB -URI https://asc.fasb.org/1943274/2147476148/220-40-50-21 + Details
Name: | us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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 Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 815 -SubTopic 20 -Name Accounting Standards Codification -Section 25 -Paragraph 6A -Publisher FASB -URI https://asc.fasb.org/1943274/2147480682/815-20-25-6A Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 815 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (f) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480237/815-40-50-5 + Details
Name: | us-gaap_DerivativeLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Nominal number of units used to calculate payment on derivative. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 8A -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-8A Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1B -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-1B Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1A -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-1A Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 815 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (f) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480237/815-40-50-5 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1I -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1I Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 505 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 18 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481112/505-10-50-18 + Details
Name: | us-gaap_DerivativeNonmonetaryNotionalAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition Fair value as of the balance sheet date of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as liabilities. + References No definition available. + Details
Name: | us-gaap_InterestRateDerivativeLiabilitiesAtFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Number of price risk derivative instruments held by the entity at the reporting date. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1B -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-1B Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1A -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-1A + Details
Name: | us-gaap_NumberOfPriceRiskDerivativesHeld
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 45 -Paragraph 28 -Subparagraph (b) -SubTopic 10 -Topic 230 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-28 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-07(7)(c)(3)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-07(7)(c)(5)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-07(7)(c)(6)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-07(7)(c)(7)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 320 -Name Accounting Standards Codification -Section S99 -Paragraph 5A -Subparagraph (SX 210.12-13A(Column F)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477271/946-320-S99-5A + Details
Name: | us-gaap_UnrealizedGainLossOnDerivatives
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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

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

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

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=tve_FuelExpenseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=tve_PurchasedPowerExpenseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BalanceSheetLocationAxis=us-gaap_AccountsPayableAndAccruedLiabilitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |