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		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Revenues from external customers	$ 845	$ 854	$ 2,510	$ 2,392
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	47	32	145	84
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)	(2)	(9)	(10)
Unallocated and Other [Member] | Shipping and Handling Costs [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	32	$ 34	96	$ 94
Unallocated and Other [Member] | By-product Sales [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	$ 18		$ 58