Business Segment Information - Summary of Segment Information (Details) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2020 USD ($) segment	Mar. 31, 2019 USD ($)
Segment Reporting [Abstract]
Number of reportable segments | segment			2
Segment Reporting Information [Line Items]
Sales	$ 871	$ 1,156	$ 1,772	$ 2,194
External Sales
Segment Reporting Information [Line Items]
Sales	871	1,156	1,772	2,194
Intersegment Sales
Segment Reporting Information [Line Items]
Sales	0	0	0	0
Commercial Truck
Segment Reporting Information [Line Items]
Sales	557	837	1,147	1,581
Aftermarket, Industrial and Trailer
Segment Reporting Information [Line Items]
Sales	314	319	625	613
Reportable Segments | Commercial Truck
Segment Reporting Information [Line Items]
Sales	588	876	1,210	1,655
Reportable Segments | Commercial Truck | External Sales
Segment Reporting Information [Line Items]
Sales	557	837	1,147	1,581
Reportable Segments | Commercial Truck | Intersegment Sales
Segment Reporting Information [Line Items]
Sales	31	39	63	74
Reportable Segments | Aftermarket, Industrial and Trailer
Segment Reporting Information [Line Items]
Sales	319	329	636	632
Reportable Segments | Aftermarket, Industrial and Trailer | External Sales
Segment Reporting Information [Line Items]
Sales	314	319	625	613
Reportable Segments | Aftermarket, Industrial and Trailer | Intersegment Sales
Segment Reporting Information [Line Items]
Sales	5	10	11	19
Eliminations
Segment Reporting Information [Line Items]
Sales	(36)	(49)	(74)	(93)
Eliminations | External Sales
Segment Reporting Information [Line Items]
Sales	0	0	0	0
Eliminations | Intersegment Sales
Segment Reporting Information [Line Items]
Sales	$ (36)	$ (49)	$ (74)	$ (93)