Purification Solutions Goodwill and Long-Lived Assets Impairment Charges - Impairment Charges and Associated Tax Benefit (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2017
Goodwill And Intangible Assets [Line Items]
Purification Solutions goodwill impairment charge		$ 92
Purification Solutions long-lived assets impairment charge		162
Provision (benefit) for income taxes		(157)	$ 26
Purification Solutions [Member]
Goodwill And Intangible Assets [Line Items]
Purification Solutions goodwill impairment charge	$ 92	92
Purification Solutions long-lived assets impairment charge	162	$ 162
Provision (benefit) for income taxes	(30)
Impairment charges, after tax	$ 224