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Risk Management Activities and Derivative Transactions Offsetting of Derivative Assets (Details) - USD ($) $ in Millions | Mar. 31, 2023 | Sep. 30, 2022
--- | --- | ---
Offsetting Assets [Line Items] |  |
Gross amounts of recognized liabilities | $ 1,412 | $ 1,160
Total derivatives not subject to master netting or similar arrangement | 25 | 152
Amount of letters of credit outstanding for credit facilities | 6 |
Forward Contract Derivative Asset, at Fair Value | 10 | 4
Derivative Liability, Not Subject to Master Netting Arrangement | 16 | 7
Derivative Asset, Fair Value, Gross Liability | 31 | 275
Offsetting Derivative Assets [Abstract] |  |
Derivative, Fair Value, Amount Offset Against Collateral, Net | 30 |
Letter of Credit |  |
Offsetting Assets [Line Items] |  |
Amount of letters of credit outstanding for credit facilities | 569 | 704
Currency Swap |  |
Offsetting Assets [Line Items] |  |
Derivative Liability, Subject to Master Netting Arrangement, after Offset | 166 | 240
Interest Rate Contract |  |
Offsetting Assets [Line Items] |  |
Gross amounts of recognized liabilities | 951 | 905
Commodity Contract under FHP |  |
Offsetting Assets [Line Items] |  |
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement | 309 |
Total derivatives not subject to master netting or similar arrangement | 6 | 123
Derivative Asset, Subject to Master Netting Arrangement, after Offset | 6 | 123
Derivative Liability, Not Subject to Master Netting Arrangement | 279 | 8
Derivative Liability, Subject to Master Netting Arrangement, after Offset | 279 | 8
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement | 36 |
Fair Value, Inputs, Level 2 |  |
Offsetting Assets [Line Items] |  |
Forward Contract Derivative Asset, at Fair Value | 10 | 4
Fair Value, Inputs, Level 2 | Commodity Contract under FHP |  |
Offsetting Assets [Line Items] |  |
Total derivatives not subject to master netting or similar arrangement | 6 | 123
Derivative Liability, Not Subject to Master Netting Arrangement | $ 279 | $ 8

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