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Commitments and Contingencies - Contingencies (Details) $ in Millions | 12 Months Ended
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Sep. 30, 2021 USD ($) Units reactors Procedures Insurance_layers | Sep. 30, 2020 USD ($) | Sep. 30, 2019 USD ($)
Contingencies |  |  |  |
Loss Contingency, Damages Sought, Value |  | $ 30 |  |
Nuclear liability insurance |  | 450 |  |
Assessment from licensees for each licensed reactor |  | $ 138 |  |
Number of licensed reactors in US | reactors |  | 95 |  |
Nuclear accident assessment limitation per year per unit |  | $ 20 |  |
Number of licensed nuclear units | Units |  | 7 |  |
Maximum assessment per nuclear incident |  | $ 963 |  |
Total amount of protection available |  | $ 13,500 |  |
Number of layers until the U.S. Congress is required to take action | Insurance_layers |  | 2 |  |
Amount of insurance available for loss at any one site |  | $ 2,100 |  |
Maximum amount of retrospective premiums |  | 128 |  |
Maximum idemnity if a covered accident tasks or keeps a nuclear unit offline |  | 490 |  |
Maximum amount of retrospective premiums |  | 43 |  |
Estimated future decommissioning cost | [1] | $ 7,002 | $ 6,785 | $ 5,616
Number of procedures for determining estimates for the costs of nuclear decommissioning | Procedures |  | 2 |  |
Amount spent to reduce emissions since 1970 |  | $ 6,800 |  |
Amount spent to reduce emissions |  | 17 | 19 | 17
Possible additional future costs for compliance with Clean Air Act requirements |  | 159 |  |
Possible additional future costs for compliance with CCR requirements |  | 789 |  |
Possible additional future costs for compliance with Clean Water requirements. |  | 148 |  |
Estimated liability for cleanup and similar environmental work on a non-discounted basis |  | 18 | 14 |
Amount of insurance available for loss at any one site, max |  | 2,800 |  |
Nuclear |  |  |  |
Contingencies |  |  |  |
Estimated future decommissioning cost |  | 3,428 | 3,278 | 3,136
Non-nuclear |  |  |  |
Contingencies |  |  |  |
Estimated future decommissioning cost |  | $ 3,574 | $ 3,507 | $ 2,480
[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 amount of property, decommissioning, and decontamination insurance available for loss at any one site to cover the cost of stabilizing or shutting down a reactor after an accident. + References No definition available. + Details
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- Definition Amount of insurance available for loss at any one site, max + References No definition available. + Details
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- Definition The amount spent to reduce emissions at power plants. + References No definition available. + Details
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- Definition The amount spent since 1970 to reduce emissions at power plants. + References No definition available. + Details
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- Definition An assessment from licensees for each licensed nuclear reactor in the United States to fund the second layer, the Secondary Financial Program. + References No definition available. + Details
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- Definition Maximum assessment per nuclear incident. + References No definition available. + Details
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- Definition The maximum idemnity per unit if an accident covered by the policy tasks or keeps a nuclear unit offline. + References No definition available. + Details
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- Definition The maximum amount of retrospective premiums that may be required for property, decommissioning, and decontamination insurance. + References No definition available. + Details
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- Definition The per year per unit limitation of the assessment for any nuclear accident + References No definition available. + Details
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- Definition For the first layer of protection all NRC nuclear plant licensees purchase nuclear insurance from American Nuclear Insurers for each nuclear plant with an operating license. + References No definition available. + Details
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- Definition The number of licensed nuclear units owned. + References No definition available. + Details
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- Definition Number of procedures for determining estimates for the costs of nuclear decommissioning + References No definition available. + Details
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- Definition The number of licensed reactors in US. + References No definition available. + Details
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- Definition The possible additional future costs for compliance with Clean Air Act requirements. + References No definition available. + Details
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- Definition The possible additional future costs for compliance with CCR requirements + References No definition available. + Details
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- Definition The possible additional future costs for compliance with Clean Water requirements. + References No definition available. + Details
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- Definition The maximum amount of retrospective premiums that could be required for accidental outage insurance. + References No definition available. + Details
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- Definition The total amount of protection available to compensate for losses arising from a nuclear event in the United States. + References No definition available. + Details
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- Definition The U.S. Congress is required to take action to provide additional funds to cover the additional losses if these layes are exhausted. + References No definition available. + Details
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- Definition Undiscounted amount of the accrual for environmental loss contingencies. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 5.Y.Q1) -URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751 + 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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