Summary of Significant Accounting Policies - Schedule of Cash and Restricted Cash (Details) - USD ($) $ in Millions	Mar. 31, 2022	Sep. 30, 2021	Mar. 31, 2021	Sep. 30, 2020
Accounting Policies [Abstract]
Cash and cash equivalents	$ 718	$ 855	$ 444
Restricted cash	55	22	28
Cash, cash equivalents and restricted cash	$ 773	$ 877	$ 472	$ 357