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		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Revenues from external customers	$ 842	$ 710	$ 1,588	$ 1,437
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	51	46	96	93
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	(5)	(1)	(10)	(2)
Unallocated and Other [Member] | Shipping and Handling Costs [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	38	30	71	61
Unallocated and Other [Member] | By-product Sales [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	$ 18	$ 17	$ 35	$ 34