Supplemental Guarantor Condensed Consolidating Financial Statements - Condensed Consolidating Statement of Operations (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Sales
Total Sales	$ 806	$ 821	$ 1,505	$ 1,630
Cost of sales	(685)	(700)	(1,295)	(1,405)
GROSS MARGIN	121	121	210	225
Selling, general and administrative	(66)	(60)	(119)	(116)
Restructuring costs	(4)	(2)	(4)	(3)
Other operating expense, net	(2)	(3)	(5)	(3)
OPERATING INCOME	49	56	82	103
Other income (expense), net	0	(2)	0	(1)
Equity in earnings of affiliates	8	7	18	17
Interest income (expense), net	(21)	(21)	(42)	(43)
INCOME BEFORE INCOME TAXES	36	40	58	76
Provision for income taxes	(13)	(7)	(19)	(14)
Equity income (loss) from continuing operations of subsidiaries	0	0	0	0
INCOME (LOSS) FROM CONTINUING OPERATIONS	23	33	39	62
LOSS FROM DISCONTINUED OPERATIONS, net of tax	0	(1)	0	(3)
NET INCOME	23	32	39	59
Less: Net income attributable to noncontrolling interests	(1)	0	(2)	(1)
NET INCOME ATTRIBUTABLE TO MERITOR, INC.	22	32	37	58
Elims
Sales
Total Sales	(44)	(44)	(82)	(87)
Cost of sales	44	44	82	87
GROSS MARGIN	0	0	0	0
Selling, general and administrative	0	0	0	0
Restructuring costs	0	0	0	0
Other operating expense, net	0	0	0	0
OPERATING INCOME	0	0	0	0
Other income (expense), net	0	0	0	0
Equity in earnings of affiliates	0	0	0	0
Interest income (expense), net	0	0	0	0
INCOME BEFORE INCOME TAXES	0	0	0	0
Provision for income taxes	0	0	0	0
Equity income (loss) from continuing operations of subsidiaries	(66)	(54)	(158)	(175)
INCOME (LOSS) FROM CONTINUING OPERATIONS	(66)	(54)	(158)	(175)
LOSS FROM DISCONTINUED OPERATIONS, net of tax	0	3	0	9
NET INCOME	(66)	(51)	(158)	(166)
Less: Net income attributable to noncontrolling interests	0	0	0	0
NET INCOME ATTRIBUTABLE TO MERITOR, INC.	(66)	(51)	(158)	(166)
Parent
Sales
Total Sales	0	0	0	0
Parent | Reportable Legal Entities
Sales
Total Sales	0	0	0	0
Cost of sales	(15)	(12)	(29)	(26)
GROSS MARGIN	(15)	(12)	(29)	(26)
Selling, general and administrative	(20)	(19)	(43)	(39)
Restructuring costs	0	0	2	0
Other operating expense, net	(2)	(3)	(2)	(3)
OPERATING INCOME	(37)	(34)	(72)	(68)
Other income (expense), net	25	35	24	34
Equity in earnings of affiliates	0	0	0	0
Interest income (expense), net	(34)	(28)	(67)	(59)
INCOME BEFORE INCOME TAXES	(46)	(27)	(115)	(93)
Provision for income taxes	15	0	35	0
Equity income (loss) from continuing operations of subsidiaries	53	60	117	154
INCOME (LOSS) FROM CONTINUING OPERATIONS	22	33	37	61
LOSS FROM DISCONTINUED OPERATIONS, net of tax	0	(1)	0	(3)
NET INCOME	22	32	37	58
Less: Net income attributable to noncontrolling interests	0	0	0	0
NET INCOME ATTRIBUTABLE TO MERITOR, INC.	22	32	37	58
Parent | Elims
Sales
Total Sales	0	0	0	0
Guarantors
Sales
Total Sales	391	420	716	837
Guarantors | Reportable Legal Entities
Sales
Total Sales	421	448	772	892
Cost of sales	(345)	(369)	(642)	(746)
GROSS MARGIN	76	79	130	146
Selling, general and administrative	(35)	(21)	(53)	(42)
Restructuring costs	(2)	(1)	(2)	(1)
Other operating expense, net	0	0	0	0
OPERATING INCOME	39	57	75	103
Other income (expense), net	(5)	(9)	(5)	(9)
Equity in earnings of affiliates	6	7	15	16
Interest income (expense), net	9	7	19	15
INCOME BEFORE INCOME TAXES	49	62	104	125
Provision for income taxes	(15)	0	(35)	0
Equity income (loss) from continuing operations of subsidiaries	13	(6)	41	21
INCOME (LOSS) FROM CONTINUING OPERATIONS	47	56	110	146
LOSS FROM DISCONTINUED OPERATIONS, net of tax	0	(2)	0	(5)
NET INCOME	47	54	110	141
Less: Net income attributable to noncontrolling interests	0	0	0	0
NET INCOME ATTRIBUTABLE TO MERITOR, INC.	47	54	110	141
Guarantors | Elims
Sales
Total Sales	30	28	56	55
Non- Guarantors
Sales
Total Sales	415	401	789	793
Non- Guarantors | Reportable Legal Entities
Sales
Total Sales	429	417	815	825
Cost of sales	(369)	(363)	(706)	(720)
GROSS MARGIN	60	54	109	105
Selling, general and administrative	(11)	(20)	(23)	(35)
Restructuring costs	(2)	(1)	(4)	(2)
Other operating expense, net	0	0	(3)	0
OPERATING INCOME	47	33	79	68
Other income (expense), net	(20)	(28)	(19)	(26)
Equity in earnings of affiliates	2	0	3	1
Interest income (expense), net	4	0	6	1
INCOME BEFORE INCOME TAXES	33	5	69	44
Provision for income taxes	(13)	(7)	(19)	(14)
Equity income (loss) from continuing operations of subsidiaries	0	0	0	0
INCOME (LOSS) FROM CONTINUING OPERATIONS	20	(2)	50	30
LOSS FROM DISCONTINUED OPERATIONS, net of tax	0	(1)	0	(4)
NET INCOME	20	(3)	50	26
Less: Net income attributable to noncontrolling interests	(1)	0	(2)	(1)
NET INCOME ATTRIBUTABLE TO MERITOR, INC.	19	(3)	48	25
Non- Guarantors | Elims
Sales
Total Sales	$ 14	$ 16	$ 26	$ 32