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Asset Retirement Obligations | 6 Months Ended
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Mar. 31, 2021
Asset Retirement Obligation Disclosure [Abstract] |
Asset Retirement Obligations | Asset Retirement Obligations During the six months ended March 31, 2021, TVA's total asset retirement obligations ("ARO") liability increased $133 million as a result of periodic accretion and revisions in estimate, partially offset by settlement projects that were conducted during the period. The nuclear and non-nuclear accretion amounts were deferred as regulatory assets. During the six months ended March 31, 2021, $36 million of the related regulatory assets were amortized into expense as these amounts were collected in rates. See Note 7 — Regulatory Assets and Liabilities. TVA maintains investment trusts to help fund its decommissioning obligations. See Note 14 — Fair Value Measurements — Investment Funds and Note 19 — Contingencies and Legal Proceedings — Contingencies — Decommissioning Costs for disclosure of the current balances of the trusts and a discussion of the trusts' objectives.
Asset Retirement Obligation Activity |
| Nuclear |  | Non-Nuclear |  | Total |
Balance at September 30, 2020 | $ | 3,278 |  |  | $ | 3,507 |  |  | $ | 6,785 |  | (1)
Settlements | (3) |  |  | (77) |  |  | (80) |  |
Revisions in estimate | 2 |  |  | 106 |  |  | 108 |  |
Accretion (recorded as regulatory asset) | 74 |  |  | 31 |  |  | 105 |  |
Balance at March 31, 2021 | $ | 3,351 |  |  | $ | 3,567 |  |  | $ | 6,918 |  | (1)
Note (1) Includes $271 million and $345 million at March 31, 2021, and September 30, 2020, respectively, in Current liabilities. The revisions in non-nuclear estimates increased $106 million for the six months ended March 31, 2021. These increases were primarily driven by revisions of certain CCR closure liabilities at Shawnee, Paradise, and Colbert, resulting from revised engineering estimates for construction costs, new vendor bids, modified closure designs, and expected costs associated with post-closure care of the closed areas.

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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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -URI http://asc.fasb.org/subtopic&trid=2175671 + Details
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