Financial Information by Segment - Sales of Equity Method Affiliate and Discounting Charges for Certain Notes Receivable and By-product Revenue (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenues from external customers	$ 821	$ 720
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	49	28
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	(3)	1
Unallocated and Other [Member] | Shipping and Handling Costs [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	32	$ 27
Unallocated and Other [Member] | By-product Sales [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	$ 20