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Risk Management Activities and Derivative Transactions Risk Management Activities and Derivative Transactions - Offsetting of Derivative Liabilities (Details) - USD ($) $ in Millions | Sep. 30, 2022 | Sep. 30, 2021
--- | --- | ---
Offsetting Liabilities [Line Items] |  |  |
Gross Amounts of Recognized Liabilities, subject to master netting or similar arrangements | $ 53 |  |
Gross Amounts Offset in the Balance Sheet | 45 |  |
Total derivatives not subject to master netting or similar arrangement | 7 | $ 3 |
Derivative Liability, Subject to Master Netting Arrangement, after Offset | 1,160 | 1,725 |
Derivative Asset, Subject to Master Netting Arrangement, after Offset | 275 | 250 |
Commodity contract derivatives | 152 | 250 |
Derivative Liability, Fair Value of Collateral | 68 |  |
Currency Swap |  |  |
Offsetting Liabilities [Line Items] |  |  |
Derivative Liability, Subject to Master Netting Arrangement, after Offset | 240 | 83 | [1]
Interest Rate Contract |  |  |
Offsetting Liabilities [Line Items] |  |  |
Derivative Liability, Subject to Master Netting Arrangement, after Offset | 905 | 1,639 | [1]
Other Contract |  |  |
Offsetting Liabilities [Line Items] |  |  |
Derivative Asset, Subject to Master Netting Arrangement, after Offset |  | 250 |
Commodity Contract under FHP |  |  |
Offsetting Liabilities [Line Items] |  |  |
Derivative Liability, Subject to Master Netting Arrangement, after Offset | 8 | 0 |
Derivative Asset, Subject to Master Netting Arrangement, after Offset | 123 | 0 |
Letter of Credit |  |  |
Offsetting Liabilities [Line Items] |  |  |
Amount of letters of credit outstanding | $ 704 | $ 1,200 |
[1] | Letters of credit of approximately $704 million and $1.2 billion were posted as collateral at September 30, 2022 and 2021, respectively, to partially secure the liability positions of one of the interest rate swaps in accordance with the collateral requirements for this derivative.

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