Business Segment Information - Summary of Segment Information (Details) $ in Millions	3 Months Ended
	Dec. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)
Segment Reporting [Abstract]
Number of reportable segments | segment	2
Segment Reporting Information [Line Items]
Sales	$ 1,038	$ 903
Commercial Truck & Trailer
Segment Reporting Information [Line Items]
Sales	786	678
Aftermarket & Industrial
Segment Reporting Information [Line Items]
Sales	252	225
Operating Segments
Segment Reporting Information [Line Items]
Sales	1,038	903
Operating Segments | Commercial Truck & Trailer
Segment Reporting Information [Line Items]
Sales	824	713
Operating Segments | Aftermarket & Industrial
Segment Reporting Information [Line Items]
Sales	257	229
Eliminations
Segment Reporting Information [Line Items]
Sales	(43)	(39)
Eliminations | Commercial Truck & Trailer
Segment Reporting Information [Line Items]
Sales	38	35
Eliminations | Aftermarket & Industrial
Segment Reporting Information [Line Items]
Sales	$ 5	$ 4