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Asset Retirement Obligations Asset Retirement Obligations (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2016 | Sep. 30, 2015
Asset Retirement Obligations |  |  |
Increase in ARO liability |  | $ 209 |
ARO-Nuclear decommissioning study update |  | 5 years |
Amortization of regulatory asset |  | $ 144 | $ 44
Balance | [1] | 3,843 | 3,169
Settlements | [1] | (133) | (58)
Change in estimate | [1] | 176 | 480
Additional obligations | [1] | 15 | 101
Accretion (recorded as regulatory asset) | [1] | 151 | 151
Balance | [1] | 4,052 | 3,843
Current portion of ARO |  | 212 | 161
Nuclear |  |  |
Asset Retirement Obligations |  |  |
Balance |  | 2,187 | 2,052
Settlements |  | 0 | 0
Change in estimate |  | 198 | 36
Additional obligations |  | 0 | 0
Revision of estimate (sequoyah license) | [1] |  | 36
Accretion (recorded as regulatory asset) |  | 107 | 99
Balance |  | 2,492 | 2,187
Non-nuclear - Closure Method Revision |  |  |
Asset Retirement Obligations |  |  |
Change in estimate |  | 32 |
Non-nuclear - Active Projects Revisions |  |  |
Asset Retirement Obligations |  |  |
Change in estimate |  | (54) |
Non-nuclear |  |  |
Asset Retirement Obligations |  |  |
Balance |  | 1,656 | 1,117
Settlements |  | (133) | (58)
Change in estimate |  | (22) | 444
Additional obligations |  | 15 | 101
Revision of estimate (EPA ruling) |  |  | 469
Revision of estimate (other non nuclear) |  |  | 25
Accretion (recorded as regulatory asset) |  | 44 | 52
Balance |  | $ 1,560 | 1,656
Plant acquisition | Non-nuclear |  |  |
Asset Retirement Obligations |  |  |
Additional obligations |  |  | 7
Coal-fired obligations | Non-nuclear |  |  |
Asset Retirement Obligations |  |  |
Additional obligations |  |  | $ 94
[1] | The current portions of the ARO liability in the amounts of $212 million and $161 million as of September 30, 2016 and 2015, respectively, are included in Accounts payable and accrued liabilities.

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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 The current period expense charged against earnings on decontaminating and decommissioning of facilities used in the normal conduct of business and not intended for resale to allocate or recognize the cost of the assets over their useful lives. + References No definition available. + 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 Amount of increase (decrease) in asset retirement obligations. + 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 increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation. + 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)(4) -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 -Topic 410 -SubTopic 20 -Section 35 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6392603&loc=d3e7123-110846 + Details
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