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Regulatory Assets and Liabilities Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Sep. 30, 2016 | Sep. 30, 2015
Regulatory Assets and Liabilities |  |  |
Current regulatory assets |  | $ 536 | $ 506
Regulatory Assets |  | 10,700 | 10,924
Yearly amortization of Deferred nuclear generating units |  | $ 237 |
Period collected in rates |  | 15 years |
Deferred Nuclear Generating Units and Construction Costs |  |  |
Regulatory Assets and Liabilities |  |  |
Balance in Regulatory asset-Construction costs |  | $ 619 |
Environmental Agreements |  |  |
Regulatory Assets and Liabilities |  |  |
Initial regulatory asset |  | 360 |
Investment in environmental agreement projects |  | 290 |
Amount to be provided to fund environmental projects |  | 60 |
Amount to be paid in civil penalties |  | $ 10 |
Environmental Cleanup Costs - Kingston Ash Spill |  |  |
Regulatory Assets and Liabilities |  |  |
Current regulatory asset amortization period |  | 12 months |
Energy Efficiency Projects | Environmental Agreements |  |  |
Regulatory Assets and Liabilities |  |  |
Regulatory asset amount expensed |  | $ 238 |
Paid to States | Environmental Agreements |  |  |
Regulatory Assets and Liabilities |  |  |
Regulatory asset amount expensed |  | 60 |
Civil Penalties | Environmental Agreements |  |  |
Regulatory Assets and Liabilities |  |  |
Regulatory asset amount expensed |  | 10 |
Derivatives Under FTP |  |  |
Regulatory Assets and Liabilities |  |  |
Net unrealized gains (losses) | [1] | (39) | (116)
Other current regulatory assets |  |  |
Regulatory Assets and Liabilities |  |  |
Current regulatory assets |  | 3 | 2
Deferred Nuclear Generating Units and Construction Costs |  |  |
Regulatory Assets and Liabilities |  |  |
Current regulatory assets |  | 237 | $ 237
Regulatory Assets |  | $ 1,100 |
[1] | Fair values of certain derivatives under the FTP that were in net liability positions totaling $30 million and $89 million at September 30, 2016 and September 30, 2015, respectively, are recorded in TVA's margin cash accounts in Other current assets. These derivatives are transacted with futures commission merchants, and cash deposits have been posted to the margin cash accounts held with each futures commission merchant to offset the net liability positions in full.

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- Definition Amount of environmental agreements to be paid in civil penalties. + References No definition available. + Details
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- Definition Amount to be provided to fund environmental projects in Alabama, Kentucky, North Carolina, and Tennessee + References No definition available. + Details
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- Definition The remaining balance in the deferred generating units regulatory asset will not continue to be amortized into rates, but will be included in the plant asset balance at completion of construction. + References No definition available. + Details
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- Definition The total initial liability recorded for environmental agreements. This was deferred as a regulatory asset, after board approval, to collect this amount in rates. + References No definition available. + Details
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- Definition The yearly expense to be charged against earnings to allocate the capitalized costs of the deferred nuclear generating units regulatory asset. + References No definition available. + Details
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- Definition The expense charged against earnings during the period to allocate the capitalized costs of regulatory assets over the periods expected to benefit from such costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.3) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 + Details
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- 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
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- Definition Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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