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Asset Retirement Obligations Asset Retirement Obligations (Tables) | 12 Months Ended
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Sep. 30, 2018
Asset Retirement Obligation Disclosure [Abstract] |
Asset Retirement Obligation Activity |
Asset Retirement Obligation Activity
| Nuclear |  | Non-Nuclear |  | Total
Balance at September 30, 2016 | $ | 2,492 |  |  | $ | 1,560 |  |  | $ | 4,052 |  |
Settlements | — |  |  | (123 | ) |  | (123 | ) |
Change in estimate | 250 |  |  | 161 |  |  | 411 |  |
Additional obligations | — |  |  | 1 |  |  | 1 |  |
Reclassification of Gallatin projects(2) | — |  |  | (188 | ) |  | (188 | ) |
Accretion (recorded to regulatory asset) | 117 |  |  | 34 |  |  | 151 |  |
Balance at September 30, 2017 | 2,859 |  |  | 1,445 |  |  | 4,304 |  | (1)
Settlements | — |  |  | (106 | ) |  | (106 | ) |
Change in estimate | — |  |  | 430 |  |  | 430 |  |
Additional obligations | — |  |  | 1 |  |  | 1 |  |
Accretion (recorded to regulatory asset) | 130 |  |  | 35 |  |  | 165 |  |
Asset Disposition | — |  |  | (15 | ) |  | (15 | ) |
Balance at September 30, 2018 | $ | 2,989 |  |  | $ | 1,790 |  |  | $ | 4,779 |  | (1)
Notes (1) The current portions of the ARO liability in the amounts of $115 million a nd $128 million as of September 30, 2018 and 2017, respectively, are included in Accounts payable and accrued liabilities. (2) See Note 8 for additional information

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- Definition Tabular disclosure of the carrying amount of a liability for asset retirement obligations. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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