Summary of Significant Accounting Policies - Reconciliation of the total cash, cash equivalents and restricted cash (Details) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Accounting Policies [Abstract]
Cash and cash equivalents	$ 241	$ 405	$ 855
Restricted cash	99	64	22
Cash, cash equivalents and restricted cash	$ 340	$ 469	$ 877	$ 357