Plant Closures (Text Block)	9 Months Ended
Jun. 30, 2025
Property, Plant and Equipment Impairment or Disposal [Abstract]
Plant Closures Disclosure	Plant Closures Background TVA must continuously evaluate all generating assets to ensure an optimal energy portfolio that provides safe, clean, and reliable power while maintaining flexibility and fiscal responsibility to the people of the Tennessee Valley. In January 2023, TVA issued its Record of Decision to retire the two coal-fired units at Cumberland Fossil Plant ("Cumberland") by the end of CY 2026 and CY 2028. In April 2024, TVA issued its Record of Decision to retire the nine coal-fired units at Kingston Fossil Plant ("Kingston") by CY 2027. TVA is evaluating the impact of retiring the balance of the coal-fired fleet by 2035, and that evaluation includes environmental reviews, public input, and TVA Board of Directors ("TVA Board") approval. TVA is also reviewing how recent executive orders impact supply and planning needs related to its coal-fired fleet. Financial Impact TVA's policy is to adjust depreciation rates to reflect the most current assumptions, ensuring units will be fully depreciated by the applicable retirement dates. TVA's decision to retire the two units at Cumberland is estimated to result in approximately $16 million of additional depreciation quarterly, which does not include any potential impact from additions or retirements to net completed plant. The cumulative impact approximates $160 million of additional depreciation since January 2023, related to this decision. In addition, TVA's decision to retire the nine units at Kingston is estimated to result in approximately $9 million of additional depreciation quarterly, which does not include any potential impact from additions or retirements to net completed plant. The cumulative impact approximates $45 million of additional depreciation since April 2024, related to this decision. TVA also recognized $12 million and $11 million in operating and maintenance expense during the nine months ended June 30, 2025 and 2024, respectively, related to additional inventory reserves and write-offs related to TVA's coal-fired fleet, including Kingston and Cumberland. Of these amounts, $4 million was recognized during both the three months ended June 30, 2025 and 2024.

TVA must continuously evaluate all generating assets to ensure an optimal energy portfolio that provides safe, clean, and reliable power while maintaining flexibility and fiscal responsibility to the people of the Tennessee Valley. In January 2023, TVA issued its Record of Decision to retire the two coal-fired units at Cumberland Fossil Plant ("Cumberland") by the end of CY 2026 and CY 2028. In April 2024, TVA issued its Record of Decision to retire the nine coal-fired units at Kingston Fossil Plant ("Kingston") by CY 2027. TVA is evaluating the impact of retiring the balance of the coal-fired fleet by 2035, and that evaluation includes environmental reviews, public input, and TVA Board of Directors ("TVA Board") approval. TVA is also reviewing how recent executive orders impact supply and planning needs related to its coal-fired fleet.

TVA's policy is to adjust depreciation rates to reflect the most current assumptions, ensuring units will be fully depreciated by the applicable retirement dates. TVA's decision to retire the two units at Cumberland is estimated to result in approximately $16 million of additional depreciation quarterly, which does not include any potential impact from additions or retirements to net completed plant. The cumulative impact approximates $160 million of additional depreciation since January 2023, related to this decision. In addition, TVA's decision to retire the nine units at Kingston is estimated to result in approximately $9 million of additional depreciation quarterly, which does not include any potential impact from additions or retirements to net completed plant. The cumulative impact approximates $45 million of additional depreciation since April 2024, related to this decision.

TVA also recognized $12 million and $11 million in operating and maintenance expense during the nine months ended June 30, 2025 and 2024, respectively, related to additional inventory reserves and write-offs related to TVA's coal-fired fleet, including Kingston and Cumberland. Of these amounts, $4 million was recognized during both the three months ended June 30, 2025 and 2024.