Income Taxes - Components of Provision (Benefit) for Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Current
Current income tax expense (benefit)	$ 33	$ 124	$ 89
Deferred
Deferred income tax expense (benefit)	(1)	(124)	5
Income tax provision	32	0	94
Foreign tax authority | Ireland
Current
Current foreign tax expense	0	0	(1)
Deferred
Deferred foreign tax expense	0	0	1
Foreign tax authority | Other Foreign
Current
Current foreign tax expense	28	120	84
Deferred
Deferred foreign tax expense	(1)	(125)	5
United States
Current
US - Federal and State	5	4	6
Deferred
US - Federal and State	$ 0	$ 1	$ (1)