Income Taxes - Reconciliation Using U.S. Statutory Rate (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Income Tax Disclosure [Abstract]
Computed tax expense at the federal statutory rate	$ 111	$ 95	$ 70
Foreign impact of taxation at different rates, repatriation, valuation allowance, and other	16	30	38
Global Intangible Low Taxed Income (GILTI)	(3)	15	23
Purification Solutions business divestiture			(179)
Impact of increase (decrease) in valuation allowance on U.S. deferred taxes	(13)	(156)	160
U.S. and state benefits from research and experimentation activities	(3)	(2)	(2)
Provision (settlement) of unrecognized tax benefits	7	2	1
Permanent differences, net	(2)	(4)	10
State taxes, net of federal effect	(2)	(8)	(19)
Provision (benefit) for income taxes	$ 111	$ (28)	$ 102