Business Segment Information - Schedule of Segment Assets (Details) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Total assets	$ 3,140	$ 2,884
Reportable Segments
Segment Reporting Information [Line Items]
Total assets	2,599	2,324
Reportable Segments | Commercial Truck
Segment Reporting Information [Line Items]
Total assets	1,920	1,666
Reportable Segments | Aftermarket & Industrial
Segment Reporting Information [Line Items]
Total assets	679	658
Corporate
Segment Reporting Information [Line Items]
Total assets	737	714
Segment Reconciling Items
Segment Reporting Information [Line Items]
Less: Accounts receivable sold under off-balance sheet factoring programs	$ (196)	$ (154)