Business Segment Information - Summary of Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Segment Reporting Information [Line Items]
Sales	$ 1,154	$ 983	$ 2,138	$ 1,872
External Sales
Segment Reporting Information [Line Items]
Sales	1,154	983	2,138	1,872
Intersegment Sales
Segment Reporting Information [Line Items]
Sales	0	0	0	0
Commercial Truck
Segment Reporting Information [Line Items]
Sales	897	742	1,645	1,402
Aftermarket & Industrial
Segment Reporting Information [Line Items]
Sales	257	241	493	470
Reportable Segments | Commercial Truck
Segment Reporting Information [Line Items]
Sales	938	777	1,723	1,468
Reportable Segments | Commercial Truck | External Sales
Segment Reporting Information [Line Items]
Sales	897	742	1,645	1,402
Reportable Segments | Commercial Truck | Intersegment Sales
Segment Reporting Information [Line Items]
Sales	41	35	78	66
Reportable Segments | Aftermarket & Industrial
Segment Reporting Information [Line Items]
Sales	262	247	503	481
Reportable Segments | Aftermarket & Industrial | External Sales
Segment Reporting Information [Line Items]
Sales	257	241	493	470
Reportable Segments | Aftermarket & Industrial | Intersegment Sales
Segment Reporting Information [Line Items]
Sales	5	6	10	11
Eliminations
Segment Reporting Information [Line Items]
Sales	(46)	(41)	(88)	(77)
Eliminations | External Sales
Segment Reporting Information [Line Items]
Sales	0	0	0	0
Eliminations | Intersegment Sales
Segment Reporting Information [Line Items]
Sales	$ (46)	$ (41)	$ (88)	$ (77)