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Risk Management Activities and Derivative Transactions Derivative Instruments That Do Not Receive Hedge Accounting Treatment (Details) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Jun. 30, 2021 USD ($) Years | Jun. 30, 2020 USD ($) | Jun. 30, 2021 USD ($) Years | Jun. 30, 2020 USD ($) | Sep. 30, 2020 USD ($)
Derivative |  |  |  |  |  |  |  |
Amount recognized for unrealized gains (losses) |  |  |  | $ 0 |  |  |  |
Change in Unrealized gains (losses) on Interest Rate Derivatives | $ (183,000,000) | $ 15,000,000 |  | (346,000,000) |  | $ (370,000,000) |  |
Interest Rate Swap |  |  |  |  |  |  |  |
Derivative |  |  |  |  |  |  |  |
Gain (loss) recognized in income on derivatives | (29,000,000) | (25,000,000) | [1] | (86,000,000) | [1] | (69,000,000) | [1] |
Fair value | (464,000,000) |  |  | (464,000,000) |  |  |  | $ (588,000,000)
Commodity Contract Derivatives |  |  |  |  |  |  |  |
Derivative |  |  |  |  |  |  |  |
Gain (loss) recognized in income on derivatives | 0 | $ (2,000,000) |  | 0 | [1] | $ (1,000,000) | [1] |
Fair value | $ 106,000,000 |  |  | $ 106,000,000 |  |  |  | $ 46,000,000
Natural Gas [Member] |  |  |  |  |  |  |  |
Derivative |  |  |  |  |  |  |  |
Number of contracts | 36 |  |  | 36 |  |  |  | 42
Derivative, Nonmonetary Notional Amount | 300,000,000 |  |  | 300,000,000 |  |  |  | 302,000,000
Fair value | $ 106,000,000 |  |  | $ 106,000,000 |  |  |  | $ 46,000,000
Number Commodity Contract Term Years | Years | 3 |  |  | 3 |  |  |  |
[1] | All of TVA's derivative instruments that do not receive hedge accounting treatment have unrealized gains (losses) that would otherwise be recognized in income but instead are deferred as regulatory assets and liabilities. As such, there were no related gains (losses) recognized in income for these unrealized gains (losses) for the three and nine months ended June 30, 2021 and 2020.(2) During the fourth quarter of 2020, TVA discontinued derivative accounting for forward coal contracts.

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- Definition The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of interest rate derivatives held at each balance sheet date. + References No definition available. + Details
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