Name:	tve_OtherDebtinstrumentInterestRateEffectivePercentage
Namespace Prefix:	tve_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

The percent of par value that debt was issued/redeemed for.

No definition available.

Name:	tve_PercentOfParValue
Namespace Prefix:	tve_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

Name:	us-gaap_DebtInstrumentInterestRateEffectivePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

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.

No definition available.

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

Amount, after accumulated amortization, of debt discount (premium).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28567-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28541-108399

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

Name:	us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The cash inflow from the issuance of long-term debt that is not secured by collateral. Excludes proceeds from tax exempt unsecured debt.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3255-108585

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

Amount of cash inflow (outflow) for debt classified as other.

No definition available.

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

The cash outflow for a borrowing supported by a written promise to pay an obligation.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585

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

Amount of cash outflow for the payment of debt classified as other, maturing after one year or the operating cycle, if longer.

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

The cash outflow to repay long-term debt that is not secured by collateral. Excludes repayments of tax exempt unsecured debt.

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

Name:	tve_RedemptionsAndMaturitiesAxis=tve_A2008SeriesBMemberDomain
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	tve_RedemptionsAndMaturitiesAxis=tve_DebtOfVariableInterestEntitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	tve_RedemptionsAndMaturitiesAxis=tve_A1997SeriesEMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	tve_RedemptionsAndMaturitiesAxis=tve_A2009SeriesBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	tve_RedemptionsAndMaturitiesAxis=tve_NotesPayableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	tve_RedemptionsAndMaturitiesAxis=tve_ElectronotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	tve_RedemptionsAndMaturitiesAxis=tve_A2018SeriesAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	tve_RedemptionsAndMaturitiesAxis=tve_TotalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	tve_DebtissuesAxis=tve_A2008SeriesBMemberDomain
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	tve_DebtissuesAxis=tve_A2009SeriesBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	tve_DebtissuesAxis=tve_A1997SeriesEMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	tve_DebtissuesAxis=tve_ElectronotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	tve_DebtissuesAxis=tve_A2018SeriesAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: