XML 172 R116.htm IDEA: XBRL DOCUMENT
v3.25.3

Benefit Plans Fair Value Measurements (Details) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Sep. 30, 2025 USD ($) Years | Sep. 30, 2024 USD ($) | Oct. 01, 2019 USD ($)
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | $ 8,837 | $ 8,959 |
Derivative liabilities |  | 4 |
Net payables | 101 | 47 |
Payables for collateral on loaned securities | $ 142 | 235 |
Voting percentage required to desolve partnership in private equity | 80.00% |  |
Fair Value, Inputs, Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | $ 1,369 | 1,396 |
Derivative liabilities |  | 1 |
Fair Value, Inputs, Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 1,639 | 2,161 |
Derivative liabilities |  | 3 |
Fair Value, Inputs, Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 24 | 65 | $ 60
Derivative liabilities |  | 0 |
Equity securities |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 740 | 670 |
Equity securities | Fair Value, Inputs, Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 727 | 668 |
Equity securities | Fair Value, Inputs, Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Equity securities | Fair Value, Inputs, Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 13 | 2 |
Preferred securities |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 2 | 3 |
Preferred securities | Fair Value, Inputs, Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Preferred securities | Fair Value, Inputs, Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 2 |
Preferred securities | Fair Value, Inputs, Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 2 | 1 |
Corporate debt securities |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 770 | 1,122 |
Corporate debt securities | Fair Value, Inputs, Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Corporate debt securities | Fair Value, Inputs, Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 764 | 1,121 |
Corporate debt securities | Fair Value, Inputs, Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 6 | 1 |
Residential mortgage-backed securities |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 523 | 572 |
Residential mortgage-backed securities | Fair Value, Inputs, Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Residential mortgage-backed securities | Fair Value, Inputs, Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 520 | 511 |
Residential mortgage-backed securities | Fair Value, Inputs, Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 3 | 61 |
Debt securities issued by U.S. Treasury and other U.S. government agencies |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 433 | 543 |
Debt securities issued by U.S. Treasury and other U.S. government agencies | Fair Value, Inputs, Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 433 | 543 |
Debt securities issued by U.S. Treasury and other U.S. government agencies | Fair Value, Inputs, Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Debt securities issued by U.S. Treasury and other U.S. government agencies | Fair Value, Inputs, Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Debt securities issued by state/local governments |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 17 | 23 |
Debt securities issued by state/local governments | Fair Value, Inputs, Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Debt securities issued by state/local governments | Fair Value, Inputs, Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 17 | 23 |
Debt securities issued by state/local governments | Fair Value, Inputs, Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Debt securities issued by foreign governments |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 18 | 19 |
Debt securities issued by foreign governments | Fair Value, Inputs, Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Debt securities issued by foreign governments | Fair Value, Inputs, Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 18 | 19 |
Debt securities issued by foreign governments | Fair Value, Inputs, Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Equity security commingled funds |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 286 | 245 |
Equity security commingled funds | Fair Value, Inputs, Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Equity security commingled funds | Fair Value, Inputs, Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Equity security commingled funds | Fair Value, Inputs, Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Debt security commingled funds |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 1,845 | 1,236 |
Debt security commingled funds | Fair Value, Inputs, Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Debt security commingled funds | Fair Value, Inputs, Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Debt security commingled funds | Fair Value, Inputs, Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Institutional mutual funds |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 196 | 180 |
Institutional mutual funds | Fair Value, Inputs, Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 196 | 180 |
Institutional mutual funds | Fair Value, Inputs, Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Institutional mutual funds | Fair Value, Inputs, Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Cash equivalents and other short-term investments |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 181 | 249 |
Cash equivalents and other short-term investments | Fair Value, Inputs, Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 10 | 5 |
Cash equivalents and other short-term investments | Fair Value, Inputs, Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 171 | 244 |
Cash equivalents and other short-term investments | Fair Value, Inputs, Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Private Credit [Member] |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 1,175 | 1,126 |
Private Credit [Member] | Fair Value, Inputs, Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Private Credit [Member] | Fair Value, Inputs, Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Private Credit [Member] | Fair Value, Inputs, Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Private equity funds measured at net asset value |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 1,290 | 1,580 |
Private equity funds measured at net asset value | Fair Value, Inputs, Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Private equity funds measured at net asset value | Fair Value, Inputs, Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Private equity funds measured at net asset value | Fair Value, Inputs, Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Private real estate funds |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 1,209 | 1,150 |
Private real estate funds | Fair Value, Inputs, Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Private real estate funds | Fair Value, Inputs, Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Private real estate funds | Fair Value, Inputs, Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Securities lending commingled funds |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 142 | 235 |
Securities lending commingled funds | Fair Value, Inputs, Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Securities lending commingled funds | Fair Value, Inputs, Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 142 | 235 |
Securities lending commingled funds | Fair Value, Inputs, Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Futures |  |  |
Defined Benefit Plan Disclosure |  |  |
Derivative liabilities | 3 | 1 |
Futures | Fair Value, Inputs, Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Derivative liabilities | 3 | 1 |
Futures | Fair Value, Inputs, Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Derivative liabilities | 0 | 0 |
Futures | Fair Value, Inputs, Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Derivative liabilities | 0 | 0 |
Purchased options |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 7 | 6 |
Purchased options | Fair Value, Inputs, Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 0 | 0 |
Purchased options | Fair Value, Inputs, Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | 7 | 6 |
Purchased options | Fair Value, Inputs, Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Fair value of gross plan assets | $ 0 | 0 |
Interest Rate Swap |  |  |
Defined Benefit Plan Disclosure |  |  |
Derivative liabilities |  | 3 |
Interest Rate Swap | Fair Value, Inputs, Level 1 |  |  |
Defined Benefit Plan Disclosure |  |  |
Derivative liabilities |  | 0 |
Interest Rate Swap | Fair Value, Inputs, Level 2 |  |  |
Defined Benefit Plan Disclosure |  |  |
Derivative liabilities |  | 3 |
Interest Rate Swap | Fair Value, Inputs, Level 3 |  |  |
Defined Benefit Plan Disclosure |  |  |
Derivative liabilities |  | $ 0 |
Minimum |  |  |
Defined Benefit Plan Disclosure |  |  |
Number of years partnerships in private equity generally continue | Years | 10 |  |
Number of one year extensions for partnerships in private equity | Years | 2 |  |
Maximum |  |  |
Defined Benefit Plan Disclosure |  |  |
Number of years partnerships in private equity generally continue | Years | 14 |  |
Number of one year extensions for partnerships in private equity | Years | 3 |  |

X
- Definition Fair value of liabilities as of the measurement date resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements. These liabilities have been segregated and restricted (usually in a trust) for the purpose of defined benefit plan benefits. + References No definition available. + Details
Name: | tve_DefinedBenefitPlanFairValueOfPlanDerivativeLiabilities
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. This amount is not reduced by non-benefit liabilities. + References No definition available. + Details
Name: | tve_FairValuePlanAssetsGross
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Net payables associated with security purchases and sales and various other payables. + References No definition available. + Details
Name: | tve_NetPayables
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The number of one year extensions for partnerships in private equity stated in a range. + References No definition available. + Details
Name: | tve_Numberofoneyearextensionsforpartnershipsinprivateequity
Namespace Prefix: | tve_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of years partnerships in private equity generally continue stated in a range. + References No definition available. + Details
Name: | tve_Numberofyearspartnershipsinprivateequitygenerallycontinue
Namespace Prefix: | tve_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Payables for collateral on loaned securities in connection with retirement system participation in securities lending program. + References No definition available. + Details
Name: | tve_PayablesForCollateralOnLoanedSecurities
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The voting percentage required to desolve a partnership in private equity. + References No definition available. + Details
Name: | tve_Votingpercentagerequiredtodesolvepartnershipinprivateequity
Namespace Prefix: | tve_
Data Type: | dtr-types:percentItemType
Balance Type: | na
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/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (k) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (i) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (l) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (g) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (j)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (j)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (j)(4) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 9: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (j)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 10: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 11: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 12: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (c)(iv)(02) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 13: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (c)(ii) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 14: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 7 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-7 Reference 15: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (q) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 16: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (m) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 17: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (h) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 18: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (f) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 19: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (e) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 20: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 + Details
Name: | us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
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: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=tve_PreferredsecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_MortgageBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_USTreasuryAndGovernmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_MunicipalBondsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_ForeignGovernmentDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=tve_EquitySecurityCommingledFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=tve_DebtSecurityCommingledFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_FixedIncomeFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_CashAndCashEquivalentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=tve_PrivateCreditMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_PrivateEquityFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=tve_PrivateRealEstateFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=tve_CashCollateralForBorrowedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_FutureMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_SwapMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |