Financial Information by Segment - Sales of Equity Method Affiliate and Discounting Charges for Certain Notes Receivable, by-product Revenue and Indirect Tax Settlement Credits (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Revenues from external customers	$ 968	$ 746
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	64	45
Unallocated and Other [Member] | Shipping and Handling Costs [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	39	33
Unallocated and Other [Member] | By-product Sales [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	28	17
Unallocated and Other [Member] | Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	$ (3)	$ (5)