Purification Solutions Goodwill and Long-Lived Assets Impairment Charges - Impairment Charges and Associated Tax Benefit (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Jun. 30, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Goodwill And Intangible Assets [Line Items]
Purification Solutions goodwill impairment charge				$ 352
Purification Solutions long-lived assets impairment charge			$ 23	210
Benefit for income taxes		$ (35)	$ (35)	(86)
Purification Solutions [Member]
Goodwill And Intangible Assets [Line Items]
Purification Solutions goodwill impairment charge	$ 353			352
Purification Solutions long-lived assets impairment charge				210
Benefit for income taxes				(80)
Impairment charges, after tax				$ 482