Financial Instruments and Fair Value Measurements - Transfer of Financial Assets Accounted for as Sales (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Transfers of financial assets during the period.	$ 2,615	$ 1,215	$ 1,189
Transfer of Financial Assets Accounted for as Sales, Amount Derecognized	$ 357	$ 323

Amount of derecognized financial assets from transactions which comprise an initial transfer and an agreement entered into in contemplation of the initial transfer resulting in retention of substantially all of the exposure to the economic return throughout the term of the transaction, at the date of derecognition.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 4D
-Subparagraph (a)
-SubTopic 20
-Topic 860
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481326/860-20-50-4D

Name:	us-gaap_TransferOfFinancialAssetsAccountedForAsSalesAmountDerecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant