Asset Retirement Obligations (Details) - USD ($) $ in Millions	9 Months Ended
Jun. 30, 2022	Sep. 30, 2021
Asset Retirement Obligations
Asset Retirement Obligation, Period Increase (Decrease)	$ 209
Amortization and Depreciation of Decontaminating and Decommissioning Assets	103
Asset Retirement Obligation, Beginning Balance	7,002
Settlements	(197)
Asset Retirement Obligation, Revision of Estimate	240
Accretion (recorded as regulatory asset)	166
Asset Retirement Obligation, Ending Balance	7,211
Current portion of ARO	(313)	$ (266)
Revision in estimate due to new depreciation rates	47
Revisions in estimate due to coal fines	119
Revision in ARO due to coal yards	57
Coal Combustion Residual Closure Liability Increase	82
Coal Combustion Residual Post-Closure Care Costs Increase/Decrease	53
Nuclear
Asset Retirement Obligations
Asset Retirement Obligation, Beginning Balance	3,428
Settlements	(2)
Asset Retirement Obligation, Revision of Estimate	3
Accretion (recorded as regulatory asset)	116
Asset Retirement Obligation, Ending Balance	3,545
Non-nuclear
Asset Retirement Obligations
Asset Retirement Obligation, Beginning Balance	3,574
Settlements	(195)
Asset Retirement Obligation, Revision of Estimate	237
Accretion (recorded as regulatory asset)	50
Asset Retirement Obligation, Ending Balance	$ 3,666

The amount of accretion recorded as a regulatory asset during the period.

No definition available.

Name:	tve_AccretionRecordedAsRegulatoryAsset
Namespace Prefix:	tve_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Coal Combustion Residual Closure Liability Increase

+ References

No definition available.

+ Details

Name:	tve_CoalCombustionResidualClosureLiabilityIncrease
Namespace Prefix:	tve_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Coal Combustion Residual Post-Closure Care Costs Increase/Decrease

+ References

No definition available.

+ Details

Name:	tve_CoalCombustionResidualPostClosureCareCostsIncreaseDecrease
Namespace Prefix:	tve_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Reconciliation of Asset Retirement Obligations [Line Items]

+ References

No definition available.

+ Details

Name:	tve_ReconciliationOfAssetRetirementObligationsLineItems
Namespace Prefix:	tve_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Revision in ARO due to coal yards

+ References

No definition available.

+ Details

Name:	tve_RevisionInARODueToCoalYards
Namespace Prefix:	tve_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Revision in estimate due to new depreciation rates

+ References

No definition available.

+ Details

Name:	tve_RevisionInEstimateDueToNewDepreciationRates
Namespace Prefix:	tve_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Revisions in estimate due to coal fines

+ References

No definition available.

+ Details

Name:	tve_RevisionsInEstimateDueToCoalFines
Namespace Prefix:	tve_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The current period expense charged against earnings on decontaminating and decommissioning of facilities used in the normal conduct of business and not intended for resale to allocate or recognize the cost of the assets over their useful lives.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3602-108585

+ Details

Name:	us-gaap_AmortizationAndDepreciationOfDecontaminatingAndDecommissioningAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 25
-Paragraph 4
-URI https://asc.fasb.org/extlink&oid=116646717&loc=d3e6290-110844

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

+ Details

Name:	us-gaap_AssetRetirementObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Current portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

+ Details

Name:	us-gaap_AssetRetirementObligationCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)(2)
-URI https://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

+ Details

Name:	us-gaap_AssetRetirementObligationLiabilitiesSettled
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of increase (decrease) in asset retirement obligations.

+ References

+ Details

Name:	us-gaap_AssetRetirementObligationPeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)(4)
-URI https://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

+ Details

Name:	us-gaap_AssetRetirementObligationRevisionOfEstimate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	tve_ReconciliationOfAssetRetirementObligationLiabilityAxis=tve_NuclearMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	tve_ReconciliationOfAssetRetirementObligationLiabilityAxis=tve_NonNuclearMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: