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Asset Retirement Obligations Asset Retirement Obligations (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2019
Liabilities Settled [Line Items] |  |  |  |
Increase in ARO liability |  | $ 217 |  |
Change in estimate | [1] | 203 | $ 1,077 |
Allen West ARO increase |  |  | 273 |
Gallatin CCR ARO increase (decrease) |  |  | 173 |
Additional obligations | [1] | 43 |  |
Balance | [1] | 7,002 | 6,785 | $ 5,616
Asset Retirement Obligation, Liabilities Settled | [1] | 242 | 114 |
Accretion (recorded as regulatory asset) | [1] | 213 | 206 |
Asset Retirement Obligation, Current |  | 266 | 345 |
Amortization and Depreciation of Decontaminating and Decommissioning Assets |  | 72 | 169 | 144
Total ARO change due to CCR |  | 122 | 129 |
Change in ARO from operating CCR facilities |  | 30 | 38 |
Change in ARO from inactive CCR facilities |  | 13 | 91 |
Increase in CCR post-closure care |  |  | 460 |
Change in plant decommissioning obligations |  |  | 19 |
ARO change due to groundwater monitoring |  | 69 |  |
Nuclear |  |  |  |
Liabilities Settled [Line Items] |  |  |  |
Change in estimate |  | 12 | 0 |
Additional obligations |  | 0 |  |
Balance |  | 3,428 | 3,278 | 3,136
Asset Retirement Obligation, Liabilities Settled |  | 11 | 1 |
Accretion (recorded as regulatory asset) |  | 149 | 143 |
Non-nuclear |  |  |  |
Liabilities Settled [Line Items] |  |  |  |
Change in estimate |  | 191 | 1,077 |
Additional obligations |  | 43 |  |
Balance |  | 3,574 | 3,507 | $ 2,480
Asset Retirement Obligation, Liabilities Settled |  | 231 | 113 |
Accretion (recorded as regulatory asset) |  | $ 64 | $ 63 |
[1] | (1) Includes $266 million a nd $345 million at September 30, 2021 and 2020, respectively, in Current liabilities. TVA implemented revised depreciation rates during the first quarter of 2022 applicable to its completed plant as a result of the completion of a new depreciation study. The study includes a decline in the service life estimates of TVA’s coal-fired plants based on current planning assumptions to potentially retire the remainder of the coal-fired fleet by 2035. As a result of the accelerated retirements reflected in the depreciation study, TVA performed an assessment of the assumptions used in the timing of cash flows related to its non-nuclear AROs. Based on the assessment, TVA identified changes to its projections of timing of certain asset retirement processes, that will be recorded in 2022.

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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 Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585 + 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://fasb.org/us-gaap/role/ref/legacyRef -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 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://fasb.org/us-gaap/role/ref/legacyRef -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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