Goodwill and Intangible Assets - Schedule of Goodwill Balances (Parenthetical) (Detail) - USD ($)	Sep. 30, 2019	Sep. 30, 2018
Purification Solutions [Member]
Goodwill And Intangible Assets [Line Items]
Accumulated impairment losses	$ 444,000,000	$ 444,000,000
Reinforcement Materials [Member]
Goodwill And Intangible Assets [Line Items]
Accumulated impairment losses	$ 0	$ 0

Amount of accumulated impairment loss for an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267

Name:	us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant