Share-Based Compensation - Fair Value of Stock Units Vested (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Performance-Based Restricted Stock Units
Schedule Of Share Based Compensation, Restricted Stock Units, Fair Value of Stock Units Vested [Line Items]
Total fair value of restricted stock units	$ 28	$ 14	$ 16
Time-Vested Restricted Stock Units
Schedule Of Share Based Compensation, Restricted Stock Units, Fair Value of Stock Units Vested [Line Items]
Total fair value of restricted stock units	$ 169	$ 169	$ 203

Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration