Supplemental Guarantor Condensed Consolidating Financial Statements - Condensed Consolidating Statement of Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Condensed Statement of Income Captions [Line Items]
Net income	$ 89	$ 67	$ 255	$ 93
Other comprehensive income (loss), net of tax	(8)	(50)	(3)	(34)
Total comprehensive income	81	17	252	59
Less: Comprehensive income attributable to noncontrolling interests	(2)	(1)	(7)	(7)
Comprehensive income attributable to Meritor, Inc.	79	16	245	52
Elims
Condensed Statement of Income Captions [Line Items]
Net income	(171)	(144)	(451)	(372)
Other comprehensive income (loss), net of tax	4	63	20	38
Total comprehensive income	(167)	(81)	(431)	(334)
Less: Comprehensive income attributable to noncontrolling interests	0	0	0	0
Comprehensive income attributable to Meritor, Inc.	(167)	(81)	(431)	(334)
Parent | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income	86	64	248	85
Other comprehensive income (loss), net of tax	(7)	(48)	(3)	(33)
Total comprehensive income	79	16	245	52
Less: Comprehensive income attributable to noncontrolling interests	0	0	0	0
Comprehensive income attributable to Meritor, Inc.	79	16	245	52
Guarantors | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income	128	103	313	264
Other comprehensive income (loss), net of tax	(2)	(57)	(9)	(45)
Total comprehensive income	126	46	304	219
Less: Comprehensive income attributable to noncontrolling interests	0	0	0	0
Comprehensive income attributable to Meritor, Inc.	126	46	304	219
Non- Guarantors | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income	46	44	145	116
Other comprehensive income (loss), net of tax	(3)	(8)	(11)	6
Total comprehensive income	43	36	134	122
Less: Comprehensive income attributable to noncontrolling interests	(2)	(1)	(7)	(7)
Comprehensive income attributable to Meritor, Inc.	$ 41	$ 35	$ 127	$ 115