Restructuring - Restructuring Activities and Related Reserves (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2019
Restructuring Cost And Reserve [Line Items]
Reserve balance	$ 12	$ 5	$ 5
Charges (gain)	2	9
Cash paid	(2)	(2)
Reserve balance	12	12	12
Severance and Employee Benefits [Member]
Restructuring Cost And Reserve [Line Items]
Reserve balance	7	1	1
Charges (gain)	1	7
Cash paid	(1)	(1)
Reserve balance	7	7	7
Environmental Remediation [Member]
Restructuring Cost And Reserve [Line Items]
Reserve balance	5	4	4
Costs charged against assets / (liabilities)		1
Reserve balance	5	5	$ 5
Asset Impairment and Accelerated Depreciation [Member]
Restructuring Cost And Reserve [Line Items]
Charges (gain)		1
Costs charged against assets / (liabilities)		(1)
Other [Member]
Restructuring Cost And Reserve [Line Items]
Charges (gain)	1	1
Cash paid	$ (1)	$ (1)