Risk Management Activities and Derivative Transactions Risk Management Activities and Derivative Transactions - Collateral (Details) - USD ($) $ in Millions	Sep. 30, 2025	Sep. 30, 2024
Derivative
Amount of letters of credit outstanding	$ 6
Likely collateral obligation increase if downgraded	22
Derivative Liability, Subject to Master Netting Arrangement, after Offset	884	$ 1,122
Collateralized Securities [Member]
Derivative
Collateral obligations	456
Credit Risk
Derivative
Derivative Liability, Subject to Master Netting Arrangement, after Offset	884
Letter of Credit
Derivative
Amount of letters of credit outstanding	498	$ 566
Interest swap collateral
Derivative
Amount of letters of credit outstanding	$ 442

The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

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Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities.

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Fair value, after effect of master netting arrangement, of financial liability or contract with one or more underlyings, notional amount or payment provision or both, and contract can be net settled by means outside contract or delivery of asset. Includes derivative subject to master netting arrangement not elected or qualified to offset. Excludes derivative not subject to master netting arrangement or similar agreement.

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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.

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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