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Summary of Significant Accounting Policies Summary of Significant Accounting Policies - Reclassificatons (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Sep. 30, 2013 | Sep. 30, 2012
Reclassifications |  |
Reclassification from Environmental cleanup costs-Kingston ash spill to Insurance recoveries | $ 47 | $ 5

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- Definition Reclassification from Environmental cleanup costs-Kingston ash spill to Insurance recoveries in the Cash flows from operating activities of the Consolidated Statements of Cash Flows + References No definition available. + Details
Name: | tve_ReclassificationfromEnvironmentalcleanupcostsKingstonashspilltoInsurancerecoveries
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | tve_ReclassificationsLineItems
Namespace Prefix: | tve_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration