Leases - Supplemental Cash Flow Information Related to Company's Leases (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 20	$ 25
Operating cash flows from finance leases	2	2
Financing cash flows from finance leases	3	3
Right-of-use assets obtained in exchange for new operating lease liabilities	6	14
Right-of-use assets obtained in exchange for new finance lease liabilities	$ 4	$ 24