Business Segment Information - Segment Income Attributable to Parent (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]
Interest expense, net	$ (12)	$ (17)	$ (25)	$ (45)
Provision for income taxes	(15)	(22)	(27)	(29)
Depreciation and amortization			(50)	(52)
Noncontrolling interests	(3)	(3)	(7)	(4)
Restructuring			(4)	(8)
Income from continuing operations attributable to Meritor, Inc.	61	63	115	95
Reportable Segments
Segment Reporting Information [Line Items]
Segment adjusted EBITDA	122	107	229	205
Reportable Segments | Commercial Truck
Segment Reporting Information [Line Items]
Segment adjusted EBITDA	78	73	147	136
Reportable Segments | Aftermarket & Industrial
Segment Reporting Information [Line Items]
Segment adjusted EBITDA	44	34	82	69
Segment Reconciling Items
Segment Reporting Information [Line Items]
Unallocated legacy and corporate income net	5	4	11	8
Interest expense, net	(12)	(17)	(25)	(45)
Provision for income taxes	(15)	(22)	(27)	(29)
Depreciation and amortization	(25)	(25)	(50)	(52)
Noncontrolling interests	(3)	(3)	(7)	(4)
Loss on sale of receivables	(2)	(1)	(3)	(2)
Restructuring	0	(2)	(4)	(8)
Brazil VAT Credit	0	22	0	22
Transaction costs (3)	$ (9)	$ 0	$ (9)	$ 0