Risk Management Activities and Derivative Transactions Fair Values of TVA Derivatives (Details) - USD ($) $ in Millions	Jun. 30, 2023	Sep. 30, 2022
Derivatives, Fair Value
Forward Contract Derivative Asset, at Fair Value	$ 8	$ 4
Fair value	78	1
Gross amounts of recognized liabilities	1,256	1,160
250 million Sterling currency swap
Derivatives, Fair Value
Fair value	(80)	(130)
250 million Sterling currency swap \| Other long-term liabilities
Derivatives, Fair Value
Fair value	(75)	(123)
250 million Sterling currency swap \| Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(5)	(7)
150 million Sterling currency swap
Derivatives, Fair Value
Fair value	(81)	(110)
150 million Sterling currency swap \| Other long-term liabilities
Derivatives, Fair Value
Fair value	(78)	(105)
150 million Sterling currency swap \| Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(3)	(5)
$1.0 billion notional interest rate swap
Derivatives, Fair Value
Fair value	(619)	(672)
$1.0 billion notional interest rate swap \| Other long-term liabilities
Derivatives, Fair Value
Fair value	(594)	(630)
$1.0 billion notional interest rate swap \| Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(19)	(9)
$1.0 billion notional interest rate swap \| Interest payable, current
Derivatives, Fair Value
Fair value	(6)	(33)
$476 million notional interest rate swap
Derivatives, Fair Value
Fair value	(218)	(233)
$476 million notional interest rate swap \| Other long-term liabilities
Derivatives, Fair Value
Fair value	(211)	(221)
$476 million notional interest rate swap \| Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(6)	(3)
$476 million notional interest rate swap \| Interest payable, current
Derivatives, Fair Value
Fair value		(9)
Commodity contract derivatives
Derivatives, Fair Value
Fair value	11	145
Commodity contract derivatives \| Other long-term assets
Derivatives, Fair Value
Fair value	1	34
Commodity contract derivatives \| Other current assets
Derivatives, Fair Value
Fair value	21	172
Commodity contract derivatives \| Other long-term liabilities
Derivatives, Fair Value
Fair value	(1)	(1)
Commodity contract derivatives \| Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(10)	(6)
Commodity Contract under FHP
Derivatives, Fair Value
Fair value	(247)	115
Commodity Contract under FHP \| Other long-term assets
Derivatives, Fair Value
Fair value		68
Commodity Contract under FHP \| Other current assets
Derivatives, Fair Value
Fair value		54
Commodity Contract under FHP \| Other long-term liabilities
Derivatives, Fair Value
Fair value	(77)
Commodity Contract under FHP \| Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(170)	(8)
Commodity Contract under FHP \| Accounts Receivable [Member]
Derivatives, Fair Value
Fair value		1
Commodity Contract not under FHP \| Other current assets
Derivatives, Fair Value
Fair value		118
Fair Value, Inputs, Level 2
Derivatives, Fair Value
Forward Contract Derivative Asset, at Fair Value	$ 8	$ 4

Fair value as of the balance sheet date of forward contract derivative assets.

No definition available.

Name:	tve_ForwardContractDerivativeAssetatFairValue
Namespace Prefix:	tve_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483444/210-20-55-22

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483466/210-20-50-3

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483444/210-20-55-7

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-4B

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-SubTopic 20
-Topic 860
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481326/860-20-50-4D

+ Details

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

- 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

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

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=tve_A250MillionSterlingCurrencySwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherNoncurrentLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=tve_A150MillionSterlingCurrencySwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=tve_A10BillionNotionalInterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=tve_InterestPayableCurrentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherNoncurrentAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherCurrentAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_AccountsReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=tve_CommodityContractNotUnderFHPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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