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Asset Retirement Obligations Asset Retirement Obligations (Details) - USD ($) $ in Millions | 12 Months Ended
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Sep. 30, 2015 | Sep. 30, 2014
Asset Retirement Obligations |  |  |
Increase in ARO liability |  | $ 674 |
Initial decommissioning estimate for nuclear |  | 7 years |
ARO-Nuclear Decommissioning Study Update |  | 5 years |
Accretion expense |  | $ 44 | $ 40
Balance | [1] | 3,169 | 3,488
Settlements (ash storage areas) | [1] | (58) | (14)
Change in estimate (coal combustion residuals rule)) | [1] | 469 |
Change in estimate (nuclear license extension) | [1] | 36 |
Change in estimate | [1] | (25) | (10)
Additional obligations | [1] | 101 |
Accretion (recorded as regulatory asset) | [1] | 151 | 177
Change in estimate (nuclear site - specific studies) | [1] |  | (472)
Balance | [1] | 3,843 | 3,169
Current portion of ARO |  | 161 | 80
Nuclear |  |  |
Asset Retirement Obligations |  |  |
Balance | [1] | 2,052 | 2,399
Settlements (ash storage areas) | [1] | 0 | 0
Change in estimate (coal combustion residuals rule)) | [1] | 0 |
Change in estimate (nuclear license extension) | [1] | 36 |
Change in estimate | [1] | 0 | 0
Additional obligations | [1] | 0 |
Accretion (recorded as regulatory asset) | [1] | 99 | 125
Change in estimate (nuclear site - specific studies) | [1] |  | (472)
Balance | [1] | 2,187 | 2,052
Non-nuclear |  |  |
Asset Retirement Obligations |  |  |
Balance | [1] | 1,117 | 1,089
Settlements (ash storage areas) | [1] | (58) | (14)
Change in estimate (coal combustion residuals rule)) | [1] | 469 |
Change in estimate (nuclear license extension) | [1] | 0 |
Change in estimate | [1] | (25) | (10)
Additional obligations | [1] | 101 |
Accretion (recorded as regulatory asset) | [1] | 52 | 52
Change in estimate (nuclear site - specific studies) | [1] |  | 0
Balance | [1] | 1,656 | $ 1,117
Plant acquisition [Member] | Non-nuclear |  |  |
Asset Retirement Obligations |  |  |
Additional obligations |  | 7 |
Coal-fired obligations [Member] | Non-nuclear |  |  |
Asset Retirement Obligations |  |  |
Additional obligations |  | $ 94 |
[1] | The current portions of ARO in the amounts of $161 million and $80 million as of September 30, 2015 and 2014, respectively, are included in Accounts payable and accrued liabilities.

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- Definition The maximum number of years in between ARO-nuclear decommissioning study updates. + References No definition available. + Details
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- Definition The amount of accretion recorded as a regulatory asset during the period. + References No definition available. + Details
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- Definition Amount of the Increase of Decrease in the amount of the asset retirement obligation as a result of the EPA ruling during the current period for changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation. + References No definition available. + Details
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- Definition Amount of the Increase or Decrease in the amount of the asset retirement obligation as a result of the nuclear license extension during the current period for changes in the amount of timing of the estimated cash flows associated with the settlement of the obligation. + References No definition available. + Details
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- Definition Amount of the Increase or Decrease in the amount of the asset retirement obligation as a result of site-specific studies during the current period for changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation. + References No definition available. + Details
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- Definition The assumption for the amount of time after plant shut, prior to June 30, 2014, that TVA based its decommissioning cost estimates on cost elements prescribed by the Nuclear Regulatory Commission to dismantle and decommission the radioactive portion of each site , which approximates the DECON method of decommissioning. + References No definition available. + Details
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- Definition Reconciliation of Asset Retirement Obligations [Line Items] + References No definition available. + Details
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- Definition Amount recognized for the passage of time, typically for liabilities, that have been discounted to their net present values. Excludes accretion associated with asset retirement obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 35 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6394232&loc=d3e17558-110866 + Details
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- Definition The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Asset Retirement Obligation -URI http://asc.fasb.org/extlink&oid=6505190 + Details
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- Definition Current portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition Amount of asset retirement obligations incurred during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition Net Increase or Decrease in the asset retirement obligation during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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