Financial Information by Segment & Geographic Area - Revenue from External Customers and Property, Plant and Equipment Information by Geographic Area (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues	$ 3,713	$ 3,994	$ 3,931
Net property, plant and equipment	1,711	1,534
United States [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues	670	733	738
Net property, plant and equipment	748	643
China [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues	931	983	972
Net property, plant and equipment	360	371
Other Countries [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues	2,112	2,278	$ 2,221
Net property, plant and equipment	$ 603	$ 520