Financial Information by Segment & Geographic Area - Revenue from External Customers and Long-Lived Asset Information by Geographic Area (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues from external customers	$ 659	$ 518	$ 710	$ 727	$ 827	$ 845	$ 844	$ 821	$ 2,614	$ 3,337	$ 3,242
Net property, plant and equipment	1,314				1,348				1,314	1,348	1,296
United States [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues from external customers									581	702	676
Net property, plant and equipment	493				572				493	572	493
China [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues from external customers									598	738	752
Net property, plant and equipment	295				264				295	264	270
Other Countries [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues from external customers									1,435	1,897	1,814
Net property, plant and equipment	$ 526				$ 512				$ 526	$ 512	$ 533