Financial Information by Segment - Revenues From External Customers That are Categorized as Unallocated and Other Reflect External Shipping and Handling Fees, The Impact of Unearned Revenue, Discounting Charges For Certain Notes Receivable (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024
Segment Reporting Information [Line Items]
Revenues from external customers	$ 936	$ 1,019	$ 1,891	$ 1,977
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	31	32	64	64
Unallocated and Other [Member] | Shipping and Handling Costs [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	29	$ 32	57	62
Unallocated and Other [Member] | Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	$ 2		$ 7	$ 2