Income Taxes - Effective Tax Rate Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Income Tax Disclosure [Abstract]
Tax expense at Ireland statutory rate	$ 17	$ 37	$ 7
State and local income taxes, net of federal benefit	(15)	(5)	(38)
Foreign tax rate differential	9	22	(1)
Notional interest deduction	(6)	(6)	(6)
Credits and incentives	(12)	(7)	(15)
Repatriation of foreign earnings	18	24	24
Foreign exchange	17	(7)	(2)
Impact of tax rate changes	(1)	0	(3)
Audit settlements and change in uncertain tax positions	(43)	(8)	(2)
Change in valuation allowance	90	(61)	94
Tax adjustments to value of investments	(38)	0	0
Tax impact of corporate equity and business restructuring transactions	1	1	30
Other	(5)	10	6
Income tax provision	$ 32	$ 0	$ 94