Leases - Supplemental Cash Flow Information Related to Company's Leases (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2020	Mar. 31, 2020
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 6	$ 12
Operating cash flows from finance leases	1	1
Financing cash flows from finance leases	1	1
Right-of-use assets obtained in exchange for new operating lease liabilities	3	5
Right-of-use assets obtained in exchange for new finance lease liabilities	$ 3	$ 23