Supplemental Guarantor Condensed Consolidating Financial Statements - Condensed Consolidating Statement of Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Condensed Statement of Income Captions [Line Items]
Net income	$ 92	$ (34)
Other comprehensive loss, net of tax	(2)	(4)
Total comprehensive income (loss)	90	(38)
Less: Comprehensive loss (income) attributable to noncontrolling interests	(3)	(3)
Comprehensive income (loss) attributable to Meritor, Inc.	87	(41)
Elims
Condensed Statement of Income Captions [Line Items]
Net income	(191)	(106)
Other comprehensive loss, net of tax	18	15
Total comprehensive income (loss)	(173)	(91)
Less: Comprehensive loss (income) attributable to noncontrolling interests	0	0
Comprehensive income (loss) attributable to Meritor, Inc.	(173)	(91)
Parent | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income	90	(36)
Other comprehensive loss, net of tax	(3)	(5)
Total comprehensive income (loss)	87	(41)
Less: Comprehensive loss (income) attributable to noncontrolling interests	0	0
Comprehensive income (loss) attributable to Meritor, Inc.	87	(41)
Guarantors | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income	112	69
Other comprehensive loss, net of tax	(8)	(7)
Total comprehensive income (loss)	104	62
Less: Comprehensive loss (income) attributable to noncontrolling interests	0	0
Comprehensive income (loss) attributable to Meritor, Inc.	104	62
Non- Guarantors | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income	81	39
Other comprehensive loss, net of tax	(9)	(7)
Total comprehensive income (loss)	72	32
Less: Comprehensive loss (income) attributable to noncontrolling interests	(3)	(3)
Comprehensive income (loss) attributable to Meritor, Inc.	$ 69	$ 29