Summary of Significant Accounting Policies - Schedule of Cash and Restricted Cash (Details) - USD ($) $ in Millions	Dec. 31, 2023	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Accounting Policies [Abstract]
Cash and cash equivalents	$ 204	$ 241	$ 317
Restricted cash	98	99	227
Cash, cash equivalents and restricted cash	$ 302	$ 340	$ 544	$ 469