Restructuring - Restructuring Activities and Related Reserves (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Restructuring Cost And Reserve [Line Items]
Reserve balance	$ 5	$ 9	$ 19
Charges	3	47	21
Costs charged against liabilities (assets)	1	(30)	(5)
Cash (paid) / received	(6)	(21)	(24)
Foreign currency translation adjustment			(2)
Reserve balance	3	5	9
Severance and Employee Benefits [Member]
Restructuring Cost And Reserve [Line Items]
Reserve balance	3	5	16
Charges	1	28	9
Cash (paid) / received	(3)	(30)	(18)
Foreign currency translation adjustment			(2)
Reserve balance	1	3	5
Environmental Remediation [Member]
Restructuring Cost And Reserve [Line Items]
Reserve balance	2	2	2
Charges	1
Cash (paid) / received	(1)
Reserve balance	2	2	2
Non-Cash Asset Impairment and Accelerated Depreciation [Member]
Restructuring Cost And Reserve [Line Items]
Charges		23	5
Costs charged against liabilities (assets)		(23)	(5)
Asset Sales [Member]
Restructuring Cost And Reserve [Line Items]
Charges		(9)
Costs charged against liabilities (assets)		(7)
Cash (paid) / received		16
Other [Member]
Restructuring Cost And Reserve [Line Items]
Reserve balance		2	1
Charges	1	5	7
Costs charged against liabilities (assets)	1
Cash (paid) / received	$ (2)	$ (7)	(6)
Reserve balance			$ 2