Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2017	Sep. 30, 2016	May 31, 2016
Significant Accounting Policies [Line Items]
Value of inventories under FIFO method	$ 29	$ 27
Buildings [Member] | Minimum [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment	20 years
Buildings [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment	25 years
Machinery and Equipment [Member] | Minimum [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment	10 years
Machinery and Equipment [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment	25 years
Other Fixed Assets [Member] | Minimum [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment	3 years
Other Fixed Assets [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment	25 years
Purification Solutions [Member]
Significant Accounting Policies [Line Items]
Percentage of fair value in excess of carrying amount			9.00%