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Risk Management Activities and Derivative Transactions Offsetting of Derivative Assets (Details) - USD ($) $ in Millions | Dec. 31, 2024 | Sep. 30, 2024
--- | --- | ---
Offsetting Assets [Line Items] |  |
Derivative Asset, Subject to Master Netting Arrangement, after Offset | $ 18 | $ 7
Amount of letters of credit outstanding for credit facilities | 6 |
Forward Contract Derivative Asset, at Fair Value | 9 | 11
Derivative Liability, Subject to Master Netting Arrangement, after Offset | 858 | 1,122
Offsetting Derivative Assets [Abstract] |  |
Derivative Asset, Fair Value, Gross Liability | 25 | 4
Letter of Credit |  |
Offsetting Assets [Line Items] |  |
Amount of letters of credit outstanding for credit facilities | 500 | 566
Currency Swap |  |
Offsetting Assets [Line Items] |  |
Derivative Liability, Subject to Master Netting Arrangement, after Offset | 136 | 116
Commodity Contract under FHP |  |
Offsetting Assets [Line Items] |  |
Derivative Asset, Subject to Master Netting Arrangement, after Offset | 6 | 0
Derivative Liability, Subject to Master Netting Arrangement, after Offset | 81 | 161
Offsetting Derivative Assets [Abstract] |  |
Derivative Asset, Subject to Master Netting Arrangement, before Offset | 31 | 4
Gross amounts of recognized liabilities | 106 | 165
Interest Rate Swap |  |
Offsetting Assets [Line Items] |  |
Derivative Liability, Subject to Master Netting Arrangement, after Offset | 635 | 840
Commodity Contract Derivatives |  |
Offsetting Assets [Line Items] |  |
Derivative Asset, Subject to Master Netting Arrangement, after Offset | 12 | 7
Derivative Liability, Subject to Master Netting Arrangement, after Offset | 6 | 5
Fair Value, Inputs, Level 2 |  |
Offsetting Assets [Line Items] |  |
Forward Contract Derivative Asset, at Fair Value | $ 9 | $ 11

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