Summary of Significant Accounting Policies - Schedule of Cash and Restricted Cash (Details) - USD ($) $ in Millions	Dec. 31, 2021	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Accounting Policies [Abstract]
Cash and cash equivalents	$ 334	$ 855	$ 416
Restricted cash	24	22	30
Cash, cash equivalents and restricted cash	$ 358	$ 877	$ 446	$ 357