Risk Management Activities and Derivative Transactions Offsetting of Derivative Assets (Details) - USD ($) $ in Millions	Dec. 31, 2022	Sep. 30, 2022
Offsetting Assets [Line Items]
Gross amounts of recognized liabilities	$ 1,178	$ 1,160
Total derivatives not subject to master netting or similar arrangement	80	152
Forward Contract Derivative Asset, at Fair Value	9	4
Derivative Liability, Not Subject to Master Netting Arrangement	9	7
Derivative Asset, Fair Value, Gross Liability	102	275
Offsetting Derivative Assets [Abstract]
Derivative, Fair Value, Amount Offset Against Collateral, Net	39
Letter of Credit
Offsetting Assets [Line Items]
Amount of letters of credit outstanding for credit facilities	586	704
Currency Swap
Offsetting Assets [Line Items]
Derivative Liability, Subject to Master Netting Arrangement, after Offset	169	240
Interest Rate Contract
Offsetting Assets [Line Items]
Gross amounts of recognized liabilities	857	905
Commodity Contract under FHP
Offsetting Assets [Line Items]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	182
Total derivatives not subject to master netting or similar arrangement	22	123
Derivative Asset, Subject to Master Netting Arrangement, after Offset	22	123
Derivative Liability, Not Subject to Master Netting Arrangement	143	8
Derivative Liability, Subject to Master Netting Arrangement, after Offset	143	8
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	61
Offsetting Derivative Assets [Abstract]
Derivative Liability, Fair Value of Collateral	3
Fair Value, Inputs, Level 2
Offsetting Assets [Line Items]
Forward Contract Derivative Asset, at Fair Value	9	4
Fair Value, Inputs, Level 2 \| Commodity Contract under FHP
Offsetting Assets [Line Items]
Total derivatives not subject to master netting or similar arrangement	22	123
Derivative Liability, Not Subject to Master Netting Arrangement	$ 143	$ 8

Fair value as of the balance sheet date of forward contract derivative assets.

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The net amount as of the balance sheet date of the fair value of derivative assets and derivative liabilities that in accordance with the entity's accounting policy were offset against collateral under a master netting arrangement.

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Fair value of securities pledged as collateral against derivative liabilities.

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