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Benefit Plans Components of Benefit Plans (Details) | 9 Months Ended
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Jun. 30, 2013 plans
Defined Benefit Plan Disclosure |
Number of defined benefit plans | 1
Number of definied contribution plans | 1
Number of unfunded post-retirement health care plans | 2

X
- Definition The number of qualified defined benefit pension plans. + References No definition available. + Details
Name: | tve_NumberOfQualifiedDefinedBenefitPlans
Namespace Prefix: | tve_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of qualified defined contribution pension plans. + References No definition available. + Details
Name: | tve_NumberOfQualifiedDefinedContributionPlans
Namespace Prefix: | tve_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of unfunded post-retirement health care plans that provide for non-vested contributions toward the cost of certain retirees' medical coverage. + References No definition available. + Details
Name: | tve_NumberOfUnfundedPostRetirementHealthCarePlans
Namespace Prefix: | tve_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration