Financial Information by Segment & Geographic Area - Sales of Equity Method Affiliate and Discounting Charges for Certain Notes Receivable (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Revenues from external customers	$ 827	$ 845	$ 844	$ 821	$ 850	$ 854	$ 818	$ 720	$ 3,337	$ 3,242	$ 2,717
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									193	116	106
Unallocated and Other [Member] | Royalties, the Impact of Unearned Revenue, the Removal of 100% of the Sales of an Equity Method Affiliate and Discounting Charges for Certain Notes Receivable [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									(13)	11	11
Unallocated and Other [Member] | Shipping and Handling Costs [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									130	$ 105	$ 95
Unallocated and Other [Member] | By-product Sales [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									$ 76