Risk Management Activities and Derivative Transactions Risk Management Activities and Derivative Transactions - Offsetting of Derivative Assets (Details) - USD ($) $ in Millions	Sep. 30, 2025	Sep. 30, 2024
Offsetting Assets [Line Items]
Amount of letters of credit outstanding	$ 6
Letter of Credit
Offsetting Assets [Line Items]
Amount of letters of credit outstanding	498	$ 566
Commodity Contract under FHP
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets, subject to master netting or similar arrangements	$ 28	$ 4

Fair value, before effects of master netting arrangements, of a financial asset or other 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 assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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+ Details

Tennessee Valley Authority 10-K