Restructuring - Restructuring Activities and Related Reserves (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Restructuring Cost And Reserve [Line Items]
Reserve balance	$ 9	$ 7	$ 5
Charges (gain)	11	19	16
Costs charged against assets (liabilities)	(2)	(1)	(2)
Cash (paid) received	(9)	(16)	(12)
Reserve balance	9	9	7
Severance and Employee Benefits [Member]
Restructuring Cost And Reserve [Line Items]
Reserve balance	5	3	1
Charges (gain)	5	14	11
Cash (paid) received	(5)	(12)	(9)
Reserve balance	5	5	3
Environmental Remediation and Decommissioning Activities [Member]
Restructuring Cost And Reserve [Line Items]
Reserve balance	4	4	4
Charges (gain)	1
Cash (paid) received	(1)
Reserve balance	4	4	4
Non-Cash Asset Impairment and Accelerated Depreciation [Member]
Restructuring Cost And Reserve [Line Items]
Charges (gain)	2	1	2
Costs charged against assets (liabilities)	(2)	(1)	(2)
Other [Member]
Restructuring Cost And Reserve [Line Items]
Charges (gain)	3	4	3
Cash (paid) received	$ (3)	$ (4)	$ (3)