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

Fair value as of the balance sheet date of forward contract derivative assets.

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Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Fair value of the assets less the liabilities of a derivative or group of derivatives.

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