Supplemental Guarantor Condensed Consolidating Financial Statements - Condensed Consolidating Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Sales
Sales	$ 1,038	$ 903
Cost of sales	(897)	(771)
GROSS MARGIN	141	132
Selling, general and administrative	(34)	(67)
Restructuring costs	0	(2)
Other operating income (expense)	0	(1)
OPERATING INCOME (LOSS)	107	62
Other income (loss), net	11	7
Equity in earnings of affiliates	9	5
Interest income (expense), net	(14)	(24)
INCOME (LOSS) BEFORE INCOME TAXES	113	50
Benefit (Provision) for income taxes	(21)	(83)
Equity income from continuing operations of subsidiaries	0	0
INCOME (LOSS) FROM CONTINUING OPERATIONS	92	(33)
LOSS FROM DISCONTINUED OPERATIONS, net of tax	0	(1)
NET INCOME (LOSS)	92	(34)
Less: Net income attributable to noncontrolling interests	(2)	(2)
NET INCOME (LOSS) ATTRIBUTABLE TO MERITOR, INC.	90	(36)
Elims
Sales
Sales	(89)	(76)
Cost of sales	89	76
GROSS MARGIN	0	0
Selling, general and administrative	0	0
Restructuring costs		0
Other operating income (expense)		0
OPERATING INCOME (LOSS)	0	0
Other income (loss), net	0	0
Equity in earnings of affiliates	0	0
Interest income (expense), net	0	0
INCOME (LOSS) BEFORE INCOME TAXES	0	0
Benefit (Provision) for income taxes	0	0
Equity income from continuing operations of subsidiaries	(191)	(106)
INCOME (LOSS) FROM CONTINUING OPERATIONS	(191)	(106)
LOSS FROM DISCONTINUED OPERATIONS, net of tax	0	0
NET INCOME (LOSS)	(191)	(106)
Less: Net income attributable to noncontrolling interests	0	0
NET INCOME (LOSS) ATTRIBUTABLE TO MERITOR, INC.	(191)	(106)
Parent
Sales
Sales	0	0
Parent | Reportable Legal Entities
Sales
Sales	0	0
Cost of sales	(15)	(19)
GROSS MARGIN	(15)	(19)
Selling, general and administrative	(25)	(28)
Restructuring costs		0
Other operating income (expense)		(1)
OPERATING INCOME (LOSS)	(40)	(48)
Other income (loss), net	0	4
Equity in earnings of affiliates	0	0
Interest income (expense), net	(32)	(37)
INCOME (LOSS) BEFORE INCOME TAXES	(72)	(81)
Benefit (Provision) for income taxes	11	(23)
Equity income from continuing operations of subsidiaries	151	69
INCOME (LOSS) FROM CONTINUING OPERATIONS	90	(35)
LOSS FROM DISCONTINUED OPERATIONS, net of tax	0	(1)
NET INCOME (LOSS)	90	(36)
Less: Net income attributable to noncontrolling interests	0	0
NET INCOME (LOSS) ATTRIBUTABLE TO MERITOR, INC.	90	(36)
Parent | Elims
Sales
Sales	0	0
Guarantors
Sales
Sales	589	468
Guarantors | Reportable Legal Entities
Sales
Sales	621	500
Cost of sales	(534)	(418)
GROSS MARGIN	87	82
Selling, general and administrative	(27)	(20)
Restructuring costs		0
Other operating income (expense)		0
OPERATING INCOME (LOSS)	60	62
Other income (loss), net	5	6
Equity in earnings of affiliates	7	4
Interest income (expense), net	12	9
INCOME (LOSS) BEFORE INCOME TAXES	84	81
Benefit (Provision) for income taxes	(12)	(49)
Equity income from continuing operations of subsidiaries	40	37
INCOME (LOSS) FROM CONTINUING OPERATIONS	112	69
LOSS FROM DISCONTINUED OPERATIONS, net of tax	0	0
NET INCOME (LOSS)	112	69
Less: Net income attributable to noncontrolling interests	0	0
NET INCOME (LOSS) ATTRIBUTABLE TO MERITOR, INC.	112	69
Guarantors | Elims
Sales
Sales	32	32
Non- Guarantors
Sales
Sales	449	435
Non- Guarantors | Reportable Legal Entities
Sales
Sales	506	479
Cost of sales	(437)	(410)
GROSS MARGIN	69	69
Selling, general and administrative	18	(19)
Restructuring costs		(2)
Other operating income (expense)		0
OPERATING INCOME (LOSS)	87	48
Other income (loss), net	6	(3)
Equity in earnings of affiliates	2	1
Interest income (expense), net	6	4
INCOME (LOSS) BEFORE INCOME TAXES	101	50
Benefit (Provision) for income taxes	(20)	(11)
Equity income from continuing operations of subsidiaries	0	0
INCOME (LOSS) FROM CONTINUING OPERATIONS	81	39
LOSS FROM DISCONTINUED OPERATIONS, net of tax	0	0
NET INCOME (LOSS)	81	39
Less: Net income attributable to noncontrolling interests	(2)	(2)
NET INCOME (LOSS) ATTRIBUTABLE TO MERITOR, INC.	79	37
Non- Guarantors | Elims
Sales
Sales	$ 57	$ 44