Supplemental Guarantor Condensed Consolidating Financial Statements - Condensed Consolidating Statement of Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Condensed Statement of Income Captions [Line Items]
Net income	$ 242	$ 74	$ 283	$ 166
Other comprehensive income (loss), net of tax	(59)	7	(33)	5
Total comprehensive income	183	81	250	171
Less: Comprehensive income attributable to noncontrolling interests	(1)	(2)	(3)	(5)
Comprehensive income attributable to Meritor, Inc.	182	79	247	166
Eliminations
Condensed Statement of Income Captions [Line Items]
Net income	(45)	(89)	(171)	(280)
Other comprehensive income (loss), net of tax	141	(2)	79	16
Total comprehensive income	96	(91)	(92)	(264)
Less: Comprehensive income attributable to noncontrolling interests	0	0	0	0
Comprehensive income attributable to Meritor, Inc.	96	(91)	(92)	(264)
Parent | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income	241	72	280	162
Other comprehensive income (loss), net of tax	(59)	7	(33)	4
Total comprehensive income	182	79	247	166
Less: Comprehensive income attributable to noncontrolling interests	0	0	0	0
Comprehensive income attributable to Meritor, Inc.	182	79	247	166
Guarantors | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income	33	73	128	185
Other comprehensive income (loss), net of tax	(70)	1	(40)	(7)
Total comprehensive income	(37)	74	88	178
Less: Comprehensive income attributable to noncontrolling interests	0	0	0	0
Comprehensive income attributable to Meritor, Inc.	(37)	74	88	178
Non- Guarantors | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income	13	18	46	99
Other comprehensive income (loss), net of tax	(71)	1	(39)	(8)
Total comprehensive income	(58)	19	7	91
Less: Comprehensive income attributable to noncontrolling interests	(1)	(2)	(3)	(5)
Comprehensive income attributable to Meritor, Inc.	$ (59)	$ 17	$ 4	$ 86