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Asset Retirement Obligations | 6 Months Ended
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Mar. 31, 2024
Asset Retirement Obligation Disclosure [Abstract] |
Asset Retirement Obligations | Asset Retirement Obligations During the six months ended March 31, 2024, TVA's total asset retirement obligations ("ARO") liability increased $103 million primarily due to revisions in estimate to non-nuclear AROs and increases from periodic accretion, partially offset by revisions in estimate to nuclear AROs and settlements related to retirement 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, 2024, $94 million of the related regulatory assets were amortized into expense as these amounts were collected in rates. See Note 8 — Regulatory Assets and Liabilities. TVA maintains investment trusts to help fund its decommissioning obligations. See Note 14 — Fair Value Measurements — Investment Funds and Note 20 — Contingencies and Legal Proceedings — Contingencies — Decommissioning Costs for a discussion of the trusts' objectives and the current balances of the trusts.
Asset Retirement Obligation Activity (in millions) |
| Nuclear |  | Non-Nuclear |  | Total |
Balance at September 30, 2023 | $ | 3,808 |  |  | $ | 3,681 |  |  | $ | 7,489 |  | (1)
Settlements | (3) |  |  | (119) |  |  | (122) |  |
Revisions in estimate | (161) |  |  | 253 |  |  | 92 |  |
Accretion (recorded as regulatory asset) | 86 |  |  | 47 |  |  | 133 |  |
Balance at March 31, 2024 | $ | 3,730 |  |  | $ | 3,862 |  |  | $ | 7,592 |  | (1)
Note (1) Includes $311 million and $272 million at March 31, 2024, and September 30, 2023, respectively, in Current liabilities. Revisions in non-nuclear estimates increased the liability balance by $253 million for the six months ended March 31, 2024. The increase was primarily attributable to a change in closure liabilities of $184 million at Gallatin Fossil Plant based on new vendor bids associated with final closure and $76 million at Cumberland based on scope changes to the interim closure plan and updated cost estimates for activities associated with final closure.

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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/disclosureRef -Topic 410 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481850/410-20-50-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 410 -SubTopic 20 -Name Accounting Standards Codification -Publisher FASB -URI https://asc.fasb.org//410-20/tableOfContent Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 50 -Paragraph 2 -SubTopic 20 -Topic 410 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481850/410-20-50-2 + Details
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