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Risk Management Activities and Derivative Transactions Fair Values of TVA Derivatives (Details) - USD ($) $ in Millions | Jun. 30, 2025 | Sep. 30, 2024
--- | --- | ---
Derivatives, Fair Value |  |
Forward Contract Derivative Asset, at Fair Value | $ 18 | $ 11
Fair value | 8 | 64
Other current assets |  |
Derivatives, Fair Value |  |
Fair value | 13 |
250 million Sterling currency swap |  |
Derivatives, Fair Value |  |
Fair value | (35) | (49)
250 million Sterling currency swap | Other long-term liabilities |  |
Derivatives, Fair Value |  |
Fair value | (31) | (45)
250 million Sterling currency swap | Accounts payable and accrued liabilities |  |
Derivatives, Fair Value |  |
Fair value | (4) | (4)
150 million Sterling currency swap |  |
Derivatives, Fair Value |  |
Fair value | (56) | (67)
150 million Sterling currency swap | Other long-term liabilities |  |
Derivatives, Fair Value |  |
Fair value | (54) | (64)
150 million Sterling currency swap | Accounts payable and accrued liabilities |  |
Derivatives, Fair Value |  |
Fair value | (2) | (3)
$1.0 billion notional interest rate swap |  |
Derivatives, Fair Value |  |
Fair value | (508) | (622)
$1.0 billion notional interest rate swap | Other long-term liabilities |  |
Derivatives, Fair Value |  |
Fair value | (470) | (586)
$1.0 billion notional interest rate swap | Accounts payable and accrued liabilities |  |
Derivatives, Fair Value |  |
Fair value | (30) | (10)
$1.0 billion notional interest rate swap | Interest payable, current |  |
Derivatives, Fair Value |  |
Fair value | (8) | (26)
Commodity contract derivatives |  |
Derivatives, Fair Value |  |
Fair value | 1 | 2
Commodity contract derivatives | Other long-term assets |  |
Derivatives, Fair Value |  |
Fair value |  | 2
Commodity contract derivatives | Other current assets |  |
Derivatives, Fair Value |  |
Fair value | 6 | 5
Commodity contract derivatives | Other long-term liabilities |  |
Derivatives, Fair Value |  |
Fair value | (2) | (2)
Commodity contract derivatives | Accounts payable and accrued liabilities |  |
Derivatives, Fair Value |  |
Fair value | (3) | (3)
Commodity Contract under FHP |  |
Derivatives, Fair Value |  |
Fair value | (1) | (161)
Gross amounts of recognized liabilities | 55 | 165
Commodity Contract under FHP | Other long-term assets |  |
Derivatives, Fair Value |  |
Fair value | 17 |
Commodity Contract under FHP | Other current assets |  |
Derivatives, Fair Value |  |
Fair value | 7 |
Commodity Contract under FHP | Other long-term liabilities |  |
Derivatives, Fair Value |  |
Fair value | (6) | (62)
Commodity Contract under FHP | Accounts payable and accrued liabilities |  |
Derivatives, Fair Value |  |
Fair value | (19) | (99)
$476 million notational interest rate swap |  |
Derivatives, Fair Value |  |
Fair value | (165) | (218)
$476 million notational interest rate swap | Other long-term liabilities |  |
Derivatives, Fair Value |  |
Fair value | (152) | (206)
$476 million notational interest rate swap | Accounts payable and accrued liabilities |  |
Derivatives, Fair Value |  |
Fair value | (12) | (3)
$476 million notational interest rate swap | Interest payable, current |  |
Derivatives, Fair Value |  |
Fair value |  | (9)
Fair Value, Inputs, Level 2 |  |
Derivatives, Fair Value |  |
Forward Contract Derivative Asset, at Fair Value | $ 18 | $ 11

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