Income Taxes - Components of Provision (Benefit) for Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Current
Current income tax expense (benefit)	$ 209	$ 90	$ 122
Deferred
Deferred income tax expense (benefit)	40	(33)	288
Income tax provision	249	57	410
Foreign tax authority | Ireland
Current
Current foreign tax expense	1	0	0
Deferred
Deferred foreign tax expense	1	0	0
Foreign tax authority | Other Foreign
Current
Current foreign tax expense	207	91	118
Deferred
Deferred foreign tax expense	40	(33)	287
United States
Current
US - Federal and State	1	(1)	4
Deferred
US - Federal and State	$ (1)	$ 0	$ 1