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Asset Retirement Obligations | 3 Months Ended
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Dec. 31, 2016
Asset Retirement Obligation Disclosure [Abstract] |
Asset Retirement Obligations | Asset Retirement Obligations During the three months ended December 31, 2016, TVA's total ARO liability increased $29 million. During the three months ended December 31, 2016, the ARO liability increased as a result of changes in estimates and periodic accretion, partially offset by settlement projects that were conducted during these periods. The nuclear and non-nuclear accretion expense was deferred as regulatory assets. During the three months ended December 31, 2016, $36 million of the related regulatory assets were amortized into expense as these amounts were collected in rates. See Note 6. TVA maintains investment trusts to help fund its decommissioning obligations. See Note 13 and Note 16 — Contingencies — Decommissioning Costs for a discussion of the trusts' objectives and the current balances of the trusts.
Asset Retirement Obligation Activity
| Nuclear |  | Non-Nuclear |  | Total |
Balance at September 30, 2016 | $ | 2,492 |  |  | $ | 1,560 |  |  | $ | 4,052 |  |
Settlements | — |  |  | (28 | ) |  | (28 | ) |
Change in estimate | — |  |  | 20 |  |  | 20 |  |
Accretion (recorded as regulatory asset) | 29 |  |  | 8 |  |  | 37 |  |
Balance at December 31, 2016 | $ | 2,521 |  |  | $ | 1,560 |  |  | $ | 4,081 |  | (1 | )
Note (1) The current portion of ARO in the amount of $200 million and $212 million is included in Accounts payable and accrued liabilities at December 31, 2016, and September 30, 2016, respectively.

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- Definition The entire disclosure for an asset retirement obligation and the associated long-lived asset. An asset retirement obligation is a legal obligation associated with the disposal or retirement from service 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 -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 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7569-110849 + Details
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