Supplemental Guarantor Condensed Consolidating Financial Statements - Condensed Consolidating Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
CURRENT ASSETS:
Cash and cash equivalents	$ 127	$ 115	$ 116	$ 88
Receivables trade and other, net	539	588
Inventories	522	477
Other current assets	52	46
TOTAL CURRENT ASSETS	1,240	1,226
NET PROPERTY	481	483
GOODWILL	418	421
OTHER ASSETS	594	596
INVESTMENTS IN SUBSIDIARIES	0	0
TOTAL ASSETS	2,733	2,726
CURRENT LIABILITIES:
Short-term debt	172	94
Accounts and notes payable	680	700
Other current liabilities	300	290
TOTAL CURRENT LIABILITIES	1,152	1,084
LONG-TERM DEBT	731	730
RETIREMENT BENEFITS	254	262
INTERCOMPANY PAYABLE (RECEIVABLE)	0	0
OTHER LIABILITIES	233	332
MEZZANINE EQUITY	1	1
EQUITY ATTRIBUTABLE TO MERITOR, INC.	329	287
NONCONTROLLING INTERESTS	33	30
TOTAL LIABILITIES, MEZZANINE EQUITY AND EQUITY	2,733	2,726
Elims
CURRENT ASSETS:
Cash and cash equivalents	0	0	0	0
Receivables trade and other, net	0	0
Inventories	0	0
Other current assets	0	0
TOTAL CURRENT ASSETS	0	0
NET PROPERTY	0	0
GOODWILL	0	0
OTHER ASSETS	0	0
INVESTMENTS IN SUBSIDIARIES	(4,637)	(4,438)
TOTAL ASSETS	(4,637)	(4,438)
CURRENT LIABILITIES:
Short-term debt	0	0
Accounts and notes payable	0	0
Other current liabilities	0	0
TOTAL CURRENT LIABILITIES	0	0
LONG-TERM DEBT	0	0
RETIREMENT BENEFITS	0	0
INTERCOMPANY PAYABLE (RECEIVABLE)	0	0
OTHER LIABILITIES	0	0
MEZZANINE EQUITY	0	0
EQUITY ATTRIBUTABLE TO MERITOR, INC.	(4,637)	(4,438)
NONCONTROLLING INTERESTS	0	0
TOTAL LIABILITIES, MEZZANINE EQUITY AND EQUITY	(4,637)	(4,438)
Parent | Reportable Legal Entities
CURRENT ASSETS:
Cash and cash equivalents	24	24	23	10
Receivables trade and other, net	5	2
Inventories	0	0
Other current assets	6	6
TOTAL CURRENT ASSETS	35	32
NET PROPERTY	23	24
GOODWILL	0	0
OTHER ASSETS	178	179
INVESTMENTS IN SUBSIDIARIES	3,744	3,583
TOTAL ASSETS	3,980	3,818
CURRENT LIABILITIES:
Short-term debt	92	47
Accounts and notes payable	49	64
Other current liabilities	79	77
TOTAL CURRENT LIABILITIES	220	188
LONG-TERM DEBT	727	726
RETIREMENT BENEFITS	234	241
INTERCOMPANY PAYABLE (RECEIVABLE)	2,419	2,325
OTHER LIABILITIES	50	50
MEZZANINE EQUITY	1	1
EQUITY ATTRIBUTABLE TO MERITOR, INC.	329	287
NONCONTROLLING INTERESTS	0	0
TOTAL LIABILITIES, MEZZANINE EQUITY AND EQUITY	3,980	3,818
Guarantors | Reportable Legal Entities
CURRENT ASSETS:
Cash and cash equivalents	8	6	3	3
Receivables trade and other, net	57	62
Inventories	268	242
Other current assets	13	12
TOTAL CURRENT ASSETS	346	322
NET PROPERTY	242	241
GOODWILL	250	250
OTHER ASSETS	192	182
INVESTMENTS IN SUBSIDIARIES	893	855
TOTAL ASSETS	1,923	1,850
CURRENT LIABILITIES:
Short-term debt	0	0
Accounts and notes payable	284	297
Other current liabilities	54	71
TOTAL CURRENT LIABILITIES	338	368
LONG-TERM DEBT	0	0
RETIREMENT BENEFITS	0	0
INTERCOMPANY PAYABLE (RECEIVABLE)	(2,659)	(2,640)
OTHER LIABILITIES	122	124
MEZZANINE EQUITY	0	0
EQUITY ATTRIBUTABLE TO MERITOR, INC.	4,122	3,998
NONCONTROLLING INTERESTS	0	0
TOTAL LIABILITIES, MEZZANINE EQUITY AND EQUITY	1,923	1,850
Non- Guarantors | Reportable Legal Entities
CURRENT ASSETS:
Cash and cash equivalents	95	85	$ 90	$ 75
Receivables trade and other, net	477	524
Inventories	254	235
Other current assets	33	28
TOTAL CURRENT ASSETS	859	872
NET PROPERTY	216	218
GOODWILL	168	171
OTHER ASSETS	224	235
INVESTMENTS IN SUBSIDIARIES	0	0
TOTAL ASSETS	1,467	1,496
CURRENT LIABILITIES:
Short-term debt	80	47
Accounts and notes payable	347	339
Other current liabilities	167	142
TOTAL CURRENT LIABILITIES	594	528
LONG-TERM DEBT	4	4
RETIREMENT BENEFITS	20	21
INTERCOMPANY PAYABLE (RECEIVABLE)	240	315
OTHER LIABILITIES	61	158
MEZZANINE EQUITY	0	0
EQUITY ATTRIBUTABLE TO MERITOR, INC.	515	440
NONCONTROLLING INTERESTS	33	30
TOTAL LIABILITIES, MEZZANINE EQUITY AND EQUITY	$ 1,467	$ 1,496