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Fair Value Measurements Fair Value Measurements Using Significant Unobservable Inputs (Details) (USD $) | 0 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended |
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Apr. 16, 2012 | Jun. 30, 2013 | Jun. 30, 2012 | Jun. 30, 2013 Private Partnerships | Jun. 30, 2012 Private Partnerships | Jun. 30, 2013 Private Partnerships | Jun. 30, 2012 Private Partnerships | Jun. 30, 2013 Commodity Contract Derivatives | Jun. 30, 2012 Commodity Contract Derivatives | Jun. 30, 2013 Commodity Contract Derivatives | Jun. 30, 2012 Commodity Contract Derivatives | Jun. 30, 2013 Interest Rate Swaption | Jun. 30, 2012 Interest Rate Swaption | Jun. 30, 2013 Interest Rate Swaption | Jun. 30, 2012 Interest Rate Swaption | Jun. 30, 2013 Minimum tons-per-year | Jun. 30, 2013 Maximum tons-per-year | Jun. 30, 2013 Assets | Jun. 30, 2013 Liabilities, Total
Fair Value Measurements |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Balances at beginning of period |  |  |  | $ 137,000,000 | $ 36,000,000 | $ 53,000,000 | $ 22,000,000 | $ (148,000,000) | $ (311,000,000) | $ (267,000,000) | $ 239,000,000 | $ 0 | $ (993,000,000) | $ 0 | $ (1,077,000,000) |  |  |  |  |  |
Purchases |  |  |  | 9,000,000 | 9,000,000 | 93,000,000 | 21,000,000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |  |  |  |  |  |
Issuances |  |  |  | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |  |  |  |  |  |
Sales |  |  |  | (1,000,000) | 0 | (3,000,000) | (2,000,000) | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |  |  |  |  |  |
Settlements |  |  |  | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 993,000,000 | 0 | 1,077,000,000 |  |  |  |  |  |
Net realized (gains) losses recognized in income |  | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net unrealized gains (losses) deferred as regulatory assets and liabilities |  |  |  | 5,000,000 | 0 | 7,000,000 | 4,000,000 | 39,000,000 | (20,000,000) | 158,000,000 | (570,000,000) | 0 | 0 | 0 | 0 |  |  |  |  |  |
Balances at end of period |  |  |  | 150,000,000 | 45,000,000 | 150,000,000 | 45,000,000 | (109,000,000) | (331,000,000) | (109,000,000) | (331,000,000) | 0 | 0 | 0 | 0 |  |  |  |  |  |
Proceeds from derivative instrument financing | (60,000,000) | 0 | (60,000,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commodity contract derivatives, fair value disclosure |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8,000,000 | 117,000,000
Fair value inputs, counterparty credit risk |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 21.00% | [1] | 21.00% | [1] |  |
Fair value measurements tons per year |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 900,000,000 |  | 1,000,000,000 |  |  |
Price per ton |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 14.45 |  | 90.31 |  |  |
Liabilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commodity contract derivatives, fair value disclosure |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8,000,000 | 117,000,000
Fair value measurements tons per year |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 900,000,000 |  | 1,000,000,000 |  |  |
Price per ton |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 14.45 |  | $ 90.31 |  |  |
[1] | Applies to only one contract.

X
- Definition The fair value of a contract to purchase commodities at favorable prices that is expected to be realized after one year (or beyond the operating cycle if longer). + References No definition available. + Details
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- Definition This item represents the amount of the total realized and unrealized gains or losses for the period which are deferred as regulatory assets and liabilities; the fair value of which assets or liabilities was or is measured on a recurring basis using significant unobservable inputs (Level 3). + References No definition available. + Details
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- Definition The fair value measurement of tons per year used to determine fair value + References No definition available. + Details
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- Definition Issues that have taken place during the period in relation to assets or liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy. + References No definition available. + Details
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- Definition Purchases that have taken place during the period in relation to assets or liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy. + References No definition available. + Details
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- Definition Sales that have taken place during the period in relation to assets or liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy. + References No definition available. + Details
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- Definition Settlements that have taken place during the period in relation to assets or liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy. + References No definition available. + Details
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Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
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- Definition This element represents an asset or liability measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances. + References No definition available. + Details
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- Definition The price per ton used for the determination of fair value. + References No definition available. + Details
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- Details
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- Definition Amount of increase (decrease) in the fair value of derivatives recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5618551-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (a),(c),(d),(e) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624171-113959 + Details
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- Details
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- Definition Risk that one party to the contract will default expressed as a percentage, used as an input to measure fair value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=25499696&loc=d3e19207-110258 + Details
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- Details
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- Definition The net cash outflow or inflow from derivative instruments during the period, which are classified as financing activities, excluding those designated as hedging instruments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 23 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3505-108585 + Details
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