Business Segment Information - Summary of Segment Information (Details) $ in Millions	3 Months Ended
	Dec. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($)
Segment Reporting [Abstract]
Number of reportable segments | segment	2
Segment Reporting Information [Line Items]
Sales	$ 901	$ 1,038
Commercial Truck
Segment Reporting Information [Line Items]
Sales	590	744
Aftermarket, Industrial and Trailer
Segment Reporting Information [Line Items]
Sales	311	294
Eliminations
Segment Reporting Information [Line Items]
Sales	(38)	(44)
Eliminations | Commercial Truck
Segment Reporting Information [Line Items]
Sales	32	35
Eliminations | Aftermarket, Industrial and Trailer
Segment Reporting Information [Line Items]
Sales	6	9
Operating Segments
Segment Reporting Information [Line Items]
Sales	901	1,038
Operating Segments | Commercial Truck
Segment Reporting Information [Line Items]
Sales	622	779
Operating Segments | Aftermarket, Industrial and Trailer
Segment Reporting Information [Line Items]
Sales	$ 317	$ 303