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Summary of Significant Accounting Policies Reclassificatons (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended
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Dec. 31, 2012
Accounting Policies [Abstract] |
Reclassification from Other, net to Regulatory assets costs | $ (5)

X
- Definition Reclassification from Other, net to Regulatory assets costs in the Cash flows from operating activities section of the Consolidated Statements of Cash Flows + References No definition available. + Details
Name: | tve_ReclassificationfromOthernettoRegulatoryassetscosts
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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