XML 81 R55.htm IDEA: XBRL DOCUMENT
v3.6.0.2

Risk Management Activities and Derivative Transactions Derivatives Under FTP (Details) $ in Millions | 3 Months Ended |
--- | --- | ---
Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Sep. 30, 2016 USD ($)
Swap |  |  |  |
Derivative |  |  |  |
Remaining terms |  | 1 |  |
Coal Contract |  |  |  |
Derivative |  |  |  |
Notional amount |  | 25,000,000 |  | 20,000,000
Fair value |  | $ (104) |  | $ (127)
Natural Gas Contract Derivatives |  |  |  |
Derivative |  |  |  |
Notional amount |  | 198,000,000 |  | 148,000,000
Fair value |  | $ 17 |  | $ 2
Closed derivative contracts |  |  |  |
Derivative |  |  |  |
Fair value |  | (1) |  | (5)
Natural Gas Contract Derivatives |  |  |  |
Derivative |  |  |  |
Fair value |  | (20) |  | $ (39)
Decrease (increase) in fuel expense |  | (11) | $ (29) |
Decrease (increase) in purchased power expense |  | $ (3) | $ (7) |
Natural Gas swap |  |  |  |
Derivative |  |  |  |
Notional amount | [1] | 15,400,000 |  | 21,052,500
Fair value | [1] | $ (20) |  | $ (39)
Maximum | Coal Contract |  |  |  |
Derivative |  |  |  |
Remaining terms |  | 2 years |  |
Maximum | Natural Gas Contract Derivatives |  |  |  |
Derivative |  |  |  |
Remaining terms |  | 4 years |  |
[1] | Fair value amounts presented are based on the net commodity position with the counterparty. Notional amounts disclosed represent the net value of contractual amounts.

X
- Definition Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
Name: | invest_DerivativeNonmonetaryNotionalAmount
Namespace Prefix: | invest_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition The decrease (increase) in fuel expense relating to the FTP. + References No definition available. + Details
Name: | tve_DecreaseIncreaseInFuelExpense
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

X
- Definition The decrease (increase) in purchased power expense related to the FTP. + References No definition available. + Details
Name: | tve_DecreaseIncreaseInPurchasedPowerExpense
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

X
- Definition Remaining terms + References No definition available. + Details
Name: | tve_Remainingterms
Namespace Prefix: | tve_
Data Type: | us-types:durationStringItemType
Balance Type: | na
Period Type: | duration

X
- 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/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13433-108611 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13495-108611 + Details
Name: | us-gaap_DerivativeFairValueOfDerivativeNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition Period the derivative contract is outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | us-gaap_DerivativeTermOfContract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=us-gaap_SwapMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=us-gaap_CoalContractMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=us-gaap_NaturalGasReservesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=tve_ClosedDerivativeContractsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | tve_DerivativesUnderFinancialTradingProgramAxis=us-gaap_NaturalGasReservesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | tve_DerivativesUnderFinancialTradingProgramAxis=tve_NaturalGasSwapMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |