Restructuring - Restructuring Activities and Related Reserves (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2017	Mar. 31, 2017
Restructuring Cost And Reserve [Line Items]
Reserve balance	$ 4	$ 5
Charges	2	2
Cash paid	(2)	(3)
Reserve balance	4	4
Severance and Employee Benefits [Member]
Restructuring Cost And Reserve [Line Items]
Reserve balance	2	3
Charges	1	1
Cash paid	(1)	(2)
Reserve balance	2	2
Environmental Remediation [Member]
Restructuring Cost And Reserve [Line Items]
Reserve balance	2	2
Reserve balance	2	2
Other [Member]
Restructuring Cost And Reserve [Line Items]
Charges	1	1
Cash paid	$ (1)	$ (1)