Financial Instruments and Fair Value Measurement - Cash and Equivalents and Restricted Cash (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Cash and equivalents	$ 2,283	$ 2,825
Restricted Cash and Investments, Current	109	92
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	2,392	2,917	$ 590	$ 1,236
Transfers of financial assets during the period.	$ 1,302	$ 2,163