Risk Management Activities and Derivative Transactions Offsetting for Derivative Liabilities (Details) $ in Millions	Jun. 30, 2021 USD ($)	Sep. 30, 2020 USD ($) Bond_issues
Offsetting Liabilities [Line Items]
Number of currency swaps outstanding \| Bond_issues		2
Accounts Receivable, before Allowance for Credit Loss, Current	$ 1,373	$ 1,401
Total derivatives not subject to master netting or similar arrangement	110	49
Gross amounts of recognized liabilities	1,717	2,250
Derivative Liability, Not Subject to Master Netting Arrangement	4	3
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	1,721	2,253
Forward Contract Derivative Asset, at Fair Value	2	13
Currency Swap
Offsetting Liabilities [Line Items]
Gross amounts of recognized liabilities	51	209
Interest Rate Contract
Offsetting Liabilities [Line Items]
Gross amounts of recognized liabilities	1,666	2,041
Letter of Credit
Offsetting Liabilities [Line Items]
Amount of letters of credit outstanding	1,114	1,500
Fair Value, Inputs, Level 2
Offsetting Liabilities [Line Items]
Forward Contract Derivative Asset, at Fair Value	$ 2	$ 13

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

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Amount, before allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business, classified as current.

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Fair value of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, not subject to a master netting arrangement.

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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Number of foreign currency exchange rate derivatives held by the entity at the reporting date.

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