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Risk Management Activities and Derivative Transactions Collateral (Details) - USD ($) $ in Millions | Mar. 31, 2024 | Sep. 30, 2023
--- | --- | ---
Derivative |  |
Amount of letters of credit outstanding | $ 6 |
Forward Contract Derivative Asset, at Fair Value | 5 | $ 11
Likely cash collateral obligation increase | 22 |
Derivative Liability, Subject to Master Netting Arrangement, after Offset | 1,149 | 991
Collateralized Securities [Member] |  |
Derivative |  |
Derivative, Collateral, Right to Reclaim Cash | 493 |
Credit Risk |  |
Derivative |  |
Derivative Liability, Subject to Master Netting Arrangement, after Offset | 1,100 |
Letter of Credit |  |
Derivative |  |
Amount of letters of credit outstanding | 516 | 535
Interest Swap Collateral |  |
Derivative |  |
Amount of letters of credit outstanding | 485 |
Interest rate swap collateral |  |
Derivative |  |
Amount of letters of credit outstanding |  | 509
Fair Value, Inputs, Level 2 |  |
Derivative |  |
Forward Contract Derivative Asset, at Fair Value | $ 5 | $ 11

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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 210 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483466/210-20-50-3 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Topic 210 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 22 -Publisher FASB -URI https://asc.fasb.org//1943274/2147483444/210-20-55-22 + Details
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