Restructuring - Restructuring Activities and Related Reserves (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2021
Restructuring Cost And Reserve [Line Items]
Reserve balance	$ 7	$ 9	$ 9
Charges (gain)	1	3
Cost charged against assets		(2)
Cash paid	(2)	(3)
Reserve balance	6	7	6
Severance and Employee Benefits [Member]
Restructuring Cost And Reserve [Line Items]
Reserve balance	3	5	5
Charges (gain)	1
Cash paid	(2)	(2)
Reserve balance	2	3	2
Non-cash Asset Impairment [Member]
Restructuring Cost And Reserve [Line Items]
Charges (gain)		2
Cost charged against assets		(2)
Other [Member]
Restructuring Cost And Reserve [Line Items]
Charges (gain)		1
Cash paid		(1)
Environmental Remediation [Member]
Restructuring Cost And Reserve [Line Items]
Reserve balance	4	4	4
Reserve balance	$ 4	$ 4	$ 4