Supplemental Guarantor Condensed Consolidating Financial Statements - Condensed Consolidating Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Sales
Total Sales	$ 903	$ 699
Cost of sales	(763)	(610)
GROSS MARGIN	140	89
Selling, general and administrative	(67)	(53)
Restructuring costs	(2)	0
Other operating expense, net	(1)	(3)
OPERATING INCOME (LOSS)	70	33
Other income (expense), net	(1)	0
Equity in earnings of affiliates	5	10
Interest income (expense), net	(24)	(21)
INCOME (LOSS) BEFORE INCOME TAXES	50	22
Provision for income taxes	(83)	(6)
Equity income from continuing operations of subsidiaries	0	0
INCOME (LOSS) FROM CONTINUING OPERATIONS	(33)	16
LOSS FROM DISCONTINUED OPERATIONS, net of tax	(1)	0
NET INCOME (LOSS)	(34)	16
Less: Net income attributable to noncontrolling interests	(2)	(1)
NET INCOME (LOSS) ATTRIBUTABLE TO MERITOR, INC.	(36)	15
Elims
Sales
Total Sales	(76)	(38)
Cost of sales	76	38
GROSS MARGIN	0	0
Selling, general and administrative	0	0
Restructuring costs	0	0
Other operating expense, net		0
OPERATING INCOME (LOSS)	0	0
Other income (expense), net	0	0
Equity in earnings of affiliates	0	0
Interest income (expense), net	0	0
INCOME (LOSS) BEFORE INCOME TAXES	0	0
Provision for income taxes	0	0
Equity income from continuing operations of subsidiaries	(106)	(91)
INCOME (LOSS) FROM CONTINUING OPERATIONS	(106)	(91)
LOSS FROM DISCONTINUED OPERATIONS, net of tax	0	0
NET INCOME (LOSS)	(106)	(91)
Less: Net income attributable to noncontrolling interests	0	0
NET INCOME (LOSS) ATTRIBUTABLE TO MERITOR, INC.	(106)	(91)
Parent
Sales
Total Sales	0	0
Parent | Reportable Legal Entities
Sales
Total Sales	0	0
Cost of sales	(14)	(14)
GROSS MARGIN	(14)	(14)
Selling, general and administrative	(28)	(23)
Restructuring costs	0	2
Other operating expense, net	(1)	0
OPERATING INCOME (LOSS)	(43)	(35)
Other income (expense), net	(1)	(1)
Equity in earnings of affiliates	0	0
Interest income (expense), net	(37)	(33)
INCOME (LOSS) BEFORE INCOME TAXES	(81)	(69)
Provision for income taxes	(23)	20
Equity income from continuing operations of subsidiaries	69	64
INCOME (LOSS) FROM CONTINUING OPERATIONS	(35)	15
LOSS FROM DISCONTINUED OPERATIONS, net of tax	(1)	0
NET INCOME (LOSS)	(36)	15
Less: Net income attributable to noncontrolling interests	0	0
NET INCOME (LOSS) ATTRIBUTABLE TO MERITOR, INC.	(36)	15
Parent | Elims
Sales
Total Sales	0	0
Guarantors
Sales
Total Sales	468	325
Guarantors | Reportable Legal Entities
Sales
Total Sales	500	351
Cost of sales	(418)	(297)
GROSS MARGIN	82	54
Selling, general and administrative	(20)	(18)
Restructuring costs	0	0
Other operating expense, net	0	0
OPERATING INCOME (LOSS)	62	36
Other income (expense), net	6	0
Equity in earnings of affiliates	4	9
Interest income (expense), net	9	10
INCOME (LOSS) BEFORE INCOME TAXES	81	55
Provision for income taxes	(49)	(20)
Equity income from continuing operations of subsidiaries	37	27
INCOME (LOSS) FROM CONTINUING OPERATIONS	69	62
LOSS FROM DISCONTINUED OPERATIONS, net of tax	0	0
NET INCOME (LOSS)	69	62
Less: Net income attributable to noncontrolling interests	0	0
NET INCOME (LOSS) ATTRIBUTABLE TO MERITOR, INC.	69	62
Guarantors | Elims
Sales
Total Sales	32	26
Non- Guarantors
Sales
Total Sales	435	374
Non- Guarantors | Reportable Legal Entities
Sales
Total Sales	479	386
Cost of sales	(407)	(337)
GROSS MARGIN	72	49
Selling, general and administrative	(19)	(12)
Restructuring costs	(2)	(2)
Other operating expense, net	0	(3)
OPERATING INCOME (LOSS)	51	32
Other income (expense), net	(6)	1
Equity in earnings of affiliates	1	1
Interest income (expense), net	4	2
INCOME (LOSS) BEFORE INCOME TAXES	50	36
Provision for income taxes	(11)	(6)
Equity income from continuing operations of subsidiaries	0	0
INCOME (LOSS) FROM CONTINUING OPERATIONS	39	30
LOSS FROM DISCONTINUED OPERATIONS, net of tax	0	0
NET INCOME (LOSS)	39	30
Less: Net income attributable to noncontrolling interests	(2)	(1)
NET INCOME (LOSS) ATTRIBUTABLE TO MERITOR, INC.	37	29
Non- Guarantors | Elims
Sales
Total Sales	$ 44	$ 12