Contingencies and Legal Proceedings	3 Months Ended
Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Contingencies and Legal Proceedings	20. Contingencies and Legal Proceedings Contingencies Nuclear Insurance. Section 170 of the Atomic Energy Act, commonly known as the Price-Anderson Act, provides a layered framework of financial protection to compensate for liability claims of members of the public for personal injury and property damages arising from a nuclear incident in the U.S. This financial protection consists of two layers of coverage. The primary level is private insurance underwritten by American Nuclear Insurers and provides public liability insurance coverage of $450 million for each nuclear power plant licensed to operate. If this amount is not sufficient to cover claims arising from a nuclear incident, the second level, Secondary Financial Protection, applies. Within the Secondary Financial Protection level, the licensee of each nuclear reactor has a contingent obligation to pay a retrospective premium, equal to its proportionate share of the loss in excess of the primary level, regardless of proximity to the incident of fault, up to a maximum of approximately $166 million per reactor per incident. With TVA's seven reactors, the maximum total contingent obligation per incident is $1.2 billion. This retrospective premium is payable at a maximum rate currently set at approximately $25 million per year per nuclear incident per reactor. Currently, 95 reactors are participating in the Secondary Financial Protection program. In the event that a nuclear incident results in public liability claims, the primary level provided by American Nuclear Insurers combined with the Secondary Financial Protection should provide up to $16.2 billion in coverage. Federal law requires that each Nuclear Regulatory Commission ("NRC") power reactor licensee obtain property insurance from private sources to cover the cost of stabilizing and decontaminating a reactor and its station site after an accident. TVA carries property, decommissioning liability, and decontamination liability insurance from Nuclear Electric Insurance Limited ("NEIL") and European Mutual Association for Nuclear Insurance. The limits available for a loss are up to $2.1 billion for two of TVA's nuclear sites and up to $2.8 billion for the remaining site. Some of this insurance may require the payment of retrospective premiums up to a maximum of approximately $114 million. TVA purchases accidental outage (business interruption) insurance for TVA's nuclear sites from NEIL. In the event that an accident covered by this policy takes a nuclear unit offline or keeps a nuclear unit offline, NEIL will pay TVA, after a waiting period, an indemnity (a set dollar amount per week) with a maximum indemnity of $490 million per unit. This insurance policy may require the payment of retrospective premiums up to a maximum of approximately $44 million, but only to the extent the retrospective premium is deemed necessary by the NEIL Board of Directors to pay losses unable to be covered by NEIL's surplus. Decommissioning Costs. TVA recognizes legal obligations associated with the future retirement of certain tangible long-lived assets related primarily to nuclear generating plants, coal-fired generating plants, hydroelectric generating plants/dams, transmission structures, and other property-related assets. See Note 11 — Asset Retirement Obligations. Nuclear Decommissioning. Provision for decommissioning costs of nuclear generating units is based on options prescribed by the NRC procedures to dismantle and decontaminate the facilities to meet the NRC criteria for license termination. At December 31, 2023, $3.8 billion, representing the discounted value of future estimated nuclear decommissioning costs, was included in nuclear AROs. The actual decommissioning costs may vary from the derived estimates because of, among other things, changes in current assumptions, such as the assumed dates of decommissioning, changes in regulatory requirements, changes in technology, and changes in the cost of labor, materials, and equipment. Utilities that own and operate nuclear plants are required to use different procedures in calculating nuclear decommissioning costs under GAAP than those that are used in calculating nuclear decommissioning costs when reporting to the NRC. The two sets of procedures produce different estimates for the costs of decommissioning primarily because of differences in the underlying assumptions. TVA bases its nuclear decommissioning estimates on site-specific cost studies. The most recent study was approved and implemented in September 2022. Site-specific cost studies are updated for each of TVA's nuclear units at least every five years. TVA maintains an NDT to provide funding for the ultimate decommissioning of its nuclear power plants. See Note 14 — Fair Value Measurements — Investment Funds. TVA monitors the value of its NDT and believes that, over the long term and before cessation of nuclear plant operations and commencement of decommissioning activities, adequate funds from investments and additional contributions, if necessary, will be available to support decommissioning. TVA's operating nuclear power units are licensed through various dates between 2033 - 2055, depending on the unit. It may be possible to extend the operating life of some of the units with approval from the NRC. See Note 8 — Regulatory Assets and Liabilities and Note 11 — Asset Retirement Obligations. Non-Nuclear Decommissioning. At December 31, 2023, $3.7 billion, representing the discounted value of future estimated non-nuclear decommissioning costs, was included in non-nuclear AROs. This decommissioning cost estimate involves estimating the amount and timing of future expenditures and making judgments concerning whether or not such costs are considered a legal obligation. Estimating the amount and timing of future expenditures includes, among other things, making projections of the timing and duration of the asset retirement process and how costs will escalate with inflation. The actual decommissioning costs may vary from the derived estimates because of changes in current assumptions, such as the assumed dates of decommissioning, changes in regulatory requirements, changes in technology, and changes in the cost of labor, materials, and equipment. TVA updates its underlying assumptions for non-nuclear decommissioning AROs at least every five years. However, material changes in underlying assumptions that impact the amount and timing of undiscounted cash flows are continuously monitored and incorporated into ARO balances in the period identified. TVA maintains an ART to help fund the ultimate decommissioning of its non-nuclear power assets. See Note 14 — Fair Value Measurements — Investment Funds. Estimates involved in determining if additional funding will be made to the ART include inflation rate, rate of return projections on the fund investments, and the planned use of other sources to fund decommissioning costs. See Note 8 — Regulatory Assets and Liabilities and Note 11 — Asset Retirement Obligations. Environmental Matters. TVA's generation activities, like those across the utility industry and in other industrial sectors, are subject to federal, state, and local environmental laws and regulations. Major areas of regulation affecting TVA's activities include air quality control, greenhouse gas ("GHG") emissions, water quality control, and management and disposal of solid and hazardous wastes. Regulations in these major areas continue to become more stringent and have, and will continue to have, a particular emphasis on climate change, renewable generation, and energy efficiency. TVA has incurred, and expects to continue to incur, substantial capital and operating and maintenance costs to comply with evolving environmental requirements primarily associated with, but not limited to, the operation of TVA's coal-fired and natural gas-fired generating units in general and emissions of pollutants from those units. Environmental requirements placed on the operation of coal-fired and other generating units using fossil fuels such as oil and natural gas will likely continue to become more restrictive over time. Failure to comply with environmental and safety requirements can result in enforcement actions and litigation, which can lead to the imposition of significant civil liability, including fines and penalties, criminal sanctions, and/or temporary or permanent closure of non-compliant facilities. Historical non-compliance can also lead to difficulty in renewing existing permits, as well as difficulty in obtaining permits to bring new generation facilities online. Other obstacles to renewal or permitting of new facilities include a proliferation of non-government organizations seeking to use litigation tools to delay or stop altogether permitting of new fossil fuel facilities in favor of renewable energy projects. TVA estimates that compliance with existing Clean Air Act requirements (excluding GHG requirements and new or proposed regulations) could lead to costs of $228 million from 2024 to 2028, which include existing controls capital projects and air operations and maintenance projects. TVA also estimates additional expenditures of $1.6 billion from 2024 to 2028 relating to TVA's coal combustion residuals ("CCR") Program, as well as expenditures of $197 million from 2024 to 2028 relating to compliance with Clean Water Act requirements. Future costs could differ from these estimates if, among other things, new environmental laws or regulations become applicable to TVA or the facilities it operates, or if existing environmental laws or regulations are revised or reinterpreted. There could also be costs that cannot reasonably be predicted at this time, due to uncertainty of actions, that could increase these estimates, and these estimates do not include expenditures expected to be incurred after 2028. Compliance with the Environmental Protection Agency's CCR rule required implementation of a groundwater monitoring program, additional engineering, and ongoing analysis. As further analyses are performed, including evaluation of monitoring results, there is the potential for additional costs for investigation and/or remediation. These costs cannot reasonably be predicted until a final remedy is selected where required. Liability for releases, natural resource damages, and required cleanup of hazardous substances is primarily regulated by the federal Comprehensive Environmental Response, Compensation, and Liability Act ("CERCLA"), the Resource Conservation and Recovery Act ("RCRA"), and other federal and parallel state statutes. In a manner similar to many other governmental entities, industries, and power systems, TVA has generated or used hazardous substances over the years. TVA operations at some facilities have resulted in releases of contaminants that TVA has addressed or is addressing consistent with state and federal requirements. At both December 31, 2023 and September 30, 2023, TVA's estimated liability for required cleanup and similar environmental work for those sites for which sufficient information is available to develop a cost estimate was approximately $16 million on a non-discounted basis and was included in Accounts payable and accrued liabilities and Other long-term liabilities on the Consolidated Balance Sheets. Additionally, the potential inclusion of new hazardous substances under CERCLA and RCRA jurisdiction could significantly affect TVA's future liability for remediating historical releases. In August 2015, Tennessee Department of Environment and Conservation ("TDEC") issued an order that includes an iterative process through which TVA and TDEC will identify and evaluate any CCR contamination risks and, if necessary, respond to such risks. As part of this process, TVA has submitted Environmental Assessment Reports ("EARs") to TDEC, and after the EARs are approved, TVA will submit Corrective Action/Risk Assessment Plans that will identify the unacceptable risks and TVA's proposed remediation. At December 31, 2023, TVA's estimated liability for costs associated with these environmental remediation activities for sites for which sufficient information is available to develop a cost estimate was approximately $26 million and was included in Accounts payable and accrued liabilities and Other long-term liabilities on the Consolidated Balance Sheets. Potential Liability Associated with Workers' Exposure to CCR Materials. In response to the 2008 ash spill at Kingston Fossil Plant, TVA hired Jacobs Engineering Group, Inc. ("Jacobs") to oversee aspects of the cleanup. After the cleanup was completed, Jacobs was sued in the U.S. District Court for the Eastern District of Tennessee ("Eastern District") by employees of a contractor involved in the cleanup and family members of some of the employees. The plaintiffs alleged that Jacobs failed to take or provide proper health precautions and misled workers about the health risks associated with exposure to coal fly ash, which is a CCR material. The plaintiffs also alleged that exposure to the fly ash caused significant illnesses, including in some cases death. Other contractor employees and family members also filed similar lawsuits against Jacobs in the Eastern District. In the third quarter of 2023, Jacobs announced that it reached a global settlement that resolved all of these lawsuits. While TVA was not a party to any of these lawsuits, TVA may potentially have an indemnity obligation to reimburse Jacobs in some circumstances. TVA does not expect any potential liability to have a material adverse impact on its results of operations or financial condition. Legal Proceedings There have been no material changes to the legal proceedings described in Note 22 — Commitments and Contingencies — Legal Proceedings of the Annual Report.

Nuclear Insurance. Section 170 of the Atomic Energy Act, commonly known as the Price-Anderson Act, provides a layered framework of financial protection to compensate for liability claims of members of the public for personal injury and property damages arising from a nuclear incident in the U.S. This financial protection consists of two layers of coverage. The primary level is private insurance underwritten by American Nuclear Insurers and provides public liability insurance coverage of $450 million for each nuclear power plant licensed to operate. If this amount is not sufficient to cover claims arising from a nuclear incident, the second level, Secondary Financial Protection, applies. Within the Secondary Financial Protection level, the licensee of each nuclear reactor has a contingent obligation to pay a retrospective premium, equal to its proportionate share of the loss in excess of the primary level, regardless of proximity to the incident of fault, up to a maximum of approximately $166 million per reactor per incident. With TVA's seven reactors, the maximum total contingent obligation per incident is $1.2 billion. This retrospective premium is payable at a maximum rate currently set at approximately $25 million per year per nuclear incident per reactor. Currently, 95 reactors are participating in the Secondary Financial Protection program.

Federal law requires that each Nuclear Regulatory Commission ("NRC") power reactor licensee obtain property insurance from private sources to cover the cost of stabilizing and decontaminating a reactor and its station site after an accident. TVA carries property, decommissioning liability, and decontamination liability insurance from Nuclear Electric Insurance Limited ("NEIL") and European Mutual Association for Nuclear Insurance. The limits available for a loss are up to $2.1 billion for two of TVA's nuclear sites and up to $2.8 billion for the remaining site. Some of this insurance may require the payment of retrospective premiums up to a maximum of approximately $114 million.

TVA purchases accidental outage (business interruption) insurance for TVA's nuclear sites from NEIL. In the event that an accident covered by this policy takes a nuclear unit offline or keeps a nuclear unit offline, NEIL will pay TVA, after a waiting period, an indemnity (a set dollar amount per week) with a maximum indemnity of $490 million per unit. This insurance policy may require the payment of retrospective premiums up to a maximum of approximately $44 million, but only to the extent the retrospective premium is deemed necessary by the NEIL Board of Directors to pay losses unable to be covered by NEIL's surplus.

Decommissioning Costs. TVA recognizes legal obligations associated with the future retirement of certain tangible long-lived assets related primarily to nuclear generating plants, coal-fired generating plants, hydroelectric generating plants/dams, transmission structures, and other property-related assets. See Note 11 — Asset Retirement Obligations.

Nuclear Decommissioning. Provision for decommissioning costs of nuclear generating units is based on options prescribed by the NRC procedures to dismantle and decontaminate the facilities to meet the NRC criteria for license termination. At December 31, 2023, $3.8 billion, representing the discounted value of future estimated nuclear decommissioning costs, was included in nuclear AROs. The actual decommissioning costs may vary from the derived estimates because of, among other things, changes in current assumptions, such as the assumed dates of decommissioning, changes in regulatory requirements, changes in technology, and changes in the cost of labor, materials, and equipment. Utilities that own and operate nuclear plants are required to use different procedures in calculating nuclear decommissioning costs under GAAP than those that are used in calculating nuclear decommissioning costs when reporting to the NRC. The two sets of procedures produce different estimates for the costs of decommissioning primarily because of differences in the underlying assumptions. TVA bases its nuclear decommissioning estimates on site-specific cost studies. The most recent study was approved and implemented in September 2022. Site-specific cost studies are updated for each of TVA's nuclear units at least every five years.

TVA maintains an NDT to provide funding for the ultimate decommissioning of its nuclear power plants. See Note 14 — Fair Value Measurements — Investment Funds. TVA monitors the value of its NDT and believes that, over the long term and before cessation of nuclear plant operations and commencement of decommissioning activities, adequate funds from investments and additional contributions, if necessary, will be available to support decommissioning. TVA's operating nuclear power units are licensed through various dates between 2033 - 2055, depending on the unit. It may be possible to extend the operating life of some of the units with approval from the NRC. See Note 8 — Regulatory Assets and Liabilities and Note 11 — Asset Retirement Obligations.

Non-Nuclear Decommissioning. At December 31, 2023, $3.7 billion, representing the discounted value of future estimated non-nuclear decommissioning costs, was included in non-nuclear AROs. This decommissioning cost estimate involves estimating the amount and timing of future expenditures and making judgments concerning whether or not such costs are considered a legal obligation. Estimating the amount and timing of future expenditures includes, among other things, making projections of the timing and duration of the asset retirement process and how costs will escalate with inflation. The actual decommissioning costs may vary from the derived estimates because of changes in current assumptions, such as the assumed dates of decommissioning, changes in regulatory requirements, changes in technology, and changes in the cost of labor, materials, and equipment. TVA updates its underlying assumptions for non-nuclear decommissioning AROs at least every five

TVA maintains an ART to help fund the ultimate decommissioning of its non-nuclear power assets. See Note 14 — Fair Value Measurements — Investment Funds. Estimates involved in determining if additional funding will be made to the ART include inflation rate, rate of return projections on the fund investments, and the planned use of other sources to fund decommissioning costs. See Note 8 — Regulatory Assets and Liabilities and Note 11 — Asset Retirement Obligations.

Environmental Matters. TVA's generation activities, like those across the utility industry and in other industrial sectors, are subject to federal, state, and local environmental laws and regulations. Major areas of regulation affecting TVA's activities include air quality control, greenhouse gas ("GHG") emissions, water quality control, and management and disposal of solid and hazardous wastes. Regulations in these major areas continue to become more stringent and have, and will continue to have, a particular emphasis on climate change, renewable generation, and energy efficiency.

TVA has incurred, and expects to continue to incur, substantial capital and operating and maintenance costs to comply with evolving environmental requirements primarily associated with, but not limited to, the operation of TVA's coal-fired and natural gas-fired generating units in general and emissions of pollutants from those units. Environmental requirements placed on the operation of coal-fired and other generating units using fossil fuels such as oil and natural gas will likely continue to become more restrictive over time. Failure to comply with environmental and safety requirements can result in enforcement actions and litigation, which can lead to the imposition of significant civil liability, including fines and penalties, criminal sanctions, and/or temporary or permanent closure of non-compliant facilities. Historical non-compliance can also lead to difficulty in renewing existing permits, as well as difficulty in obtaining permits to bring new generation facilities online. Other obstacles to renewal or permitting of new facilities include a proliferation of non-government organizations seeking to use litigation tools to delay or stop altogether permitting of new fossil fuel facilities in favor of renewable energy projects.

TVA estimates that compliance with existing Clean Air Act requirements (excluding GHG requirements and new or proposed regulations) could lead to costs of $228 million from 2024 to 2028, which include existing controls capital projects and air operations and maintenance projects. TVA also estimates additional expenditures of $1.6 billion from 2024 to 2028 relating to TVA's coal combustion residuals ("CCR") Program, as well as expenditures of $197 million from 2024 to 2028 relating to compliance with Clean Water Act requirements. Future costs could differ from these estimates if, among other things, new environmental laws or regulations become applicable to TVA or the facilities it operates, or if existing environmental laws or regulations are revised or reinterpreted. There could also be costs that cannot reasonably be predicted at this time, due to uncertainty of actions, that could increase these estimates, and these estimates do not include expenditures expected to be incurred after 2028.

Compliance with the Environmental Protection Agency's CCR rule required implementation of a groundwater monitoring program, additional engineering, and ongoing analysis. As further analyses are performed, including evaluation of monitoring results, there is the potential for additional costs for investigation and/or remediation. These costs cannot reasonably be predicted until a final remedy is selected where required.

Liability for releases, natural resource damages, and required cleanup of hazardous substances is primarily regulated by the federal Comprehensive Environmental Response, Compensation, and Liability Act ("CERCLA"), the Resource Conservation and Recovery Act ("RCRA"), and other federal and parallel state statutes. In a manner similar to many other governmental entities, industries, and power systems, TVA has generated or used hazardous substances over the years. TVA operations at some facilities have resulted in releases of contaminants that TVA has addressed or is addressing consistent with state and federal requirements. At both December 31, 2023 and September 30, 2023, TVA's estimated liability for required cleanup and similar environmental work for those sites for which sufficient information is available to develop a cost estimate was approximately $16 million on a non-discounted basis and was included in Accounts payable and accrued liabilities and Other long-term liabilities on the Consolidated Balance Sheets. Additionally, the potential inclusion of new hazardous substances under CERCLA and RCRA jurisdiction could significantly affect TVA's future liability for remediating historical releases.

In August 2015, Tennessee Department of Environment and Conservation ("TDEC") issued an order that includes an iterative process through which TVA and TDEC will identify and evaluate any CCR contamination risks and, if necessary, respond to such risks. As part of this process, TVA has submitted Environmental Assessment Reports ("EARs") to TDEC, and after the EARs are approved, TVA will submit Corrective Action/Risk Assessment Plans that will identify the unacceptable risks and TVA's proposed remediation. At December 31, 2023, TVA's estimated liability for costs associated with these environmental remediation activities for sites for which sufficient information is available to develop a cost estimate was approximately $26 million and was included in Accounts payable and accrued liabilities and Other long-term liabilities on the Consolidated Balance Sheets.

Potential Liability Associated with Workers' Exposure to CCR Materials. In response to the 2008 ash spill at Kingston Fossil Plant, TVA hired Jacobs Engineering Group, Inc. ("Jacobs") to oversee aspects of the cleanup. After the cleanup was completed, Jacobs was sued in the U.S. District Court for the Eastern District of Tennessee ("Eastern District") by employees of a contractor involved in the cleanup and family members of some of the employees. The plaintiffs alleged that Jacobs failed to take or provide proper health precautions and misled workers about the health risks associated with exposure to coal fly ash,

which is a CCR material. The plaintiffs also alleged that exposure to the fly ash caused significant illnesses, including in some cases death. Other contractor employees and family members also filed similar lawsuits against Jacobs in the Eastern District. In the third quarter of 2023, Jacobs announced that it reached a global settlement that resolved all of these lawsuits. While TVA was not a party to any of these lawsuits, TVA may potentially have an indemnity obligation to reimburse Jacobs in some circumstances. TVA does not expect any potential liability to have a material adverse impact on its results of operations or financial condition.