Financial Information by Segment & Geographic Area - Sales of Equity Method Affiliate, Discounting Charges for Certain Notes Receivable, Indirect Tax Settlement Credits, and Insurance Recoveries (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Revenues from external customers	$ 3,409	$ 2,614	$ 3,337
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	223	172	193
Unallocated and Other [Member] | Shipping and Handling Costs [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	153	113	130
Unallocated and Other [Member] | By-product Sales [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	73	62	76
Unallocated and Other [Member] | Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	$ (3)	$ (3)	$ (13)