Business Segment Information - Schedule of Segment Assets (Details) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Total assets	$ 3,225	$ 2,815
Reportable Segments
Segment Reporting Information [Line Items]
Total assets	2,492	2,474
Reportable Segments | Commercial Truck
Segment Reporting Information [Line Items]
Total assets	1,682	1,659
Reportable Segments | Aftermarket, Industrial and Trailer
Segment Reporting Information [Line Items]
Total assets	810	815
Corporate
Segment Reporting Information [Line Items]
Total assets	977	567
Segment Reconciling Items
Segment Reporting Information [Line Items]
Less: Accounts receivable sold under off-balance sheet factoring programs	$ (244)	$ (226)