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