Leases - Supplemental Cash Flow Information Related to Company's Leases (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 17	$ 18	$ 18
Operating cash flows from finance leases	2	1	2
Financing cash flows from finance leases	6	4	3
Right-of-use assets obtained in exchange for new operating lease liabilities	8	9	11
Right-of-use assets obtained in exchange for new finance lease liabilities	$ 11	$ 2	$ 4