Leases - Supplemental Balance Sheet Information Related to Company's Leases (Detail) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022
Lease ROU assets:
Operating	$ 101	$ 96
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Other assets	Other assets
Finance	$ 39	$ 41
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Net property, plant and equipment	Net property, plant and equipment
Total lease ROU assets	$ 140	$ 137
Lease liabilities:
Operating	$ 15	$ 14
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Accounts payable and accrued liabilities	Accounts payable and accrued liabilities
Finance	$ 4	$ 3
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Current portion of long-term debt	Current portion of long-term debt
Operating	$ 84	$ 83
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other liabilities	Other liabilities
Finance	$ 24	$ 26
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Long-term debt	Long-term debt
Total lease liabilities	$ 127	$ 126