SUPPLEMENTAL PARENT AND GUARANTOR CONDENSED CONSOLIDATING FINANCIAL STATEMENTS - Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
CURRENT ASSETS
Cash and cash equivalents	$ 108	$ 115
Receivables, trade and other, net	551	588
Inventories	526	477
Other current assets	31	46
TOTAL CURRENT ASSETS	1,216	1,226
NET PROPERTY	515	483
GOODWILL	478	421	$ 414	$ 429
OTHER ASSETS	606	596
INVESTMENTS IN SUBSIDIARIES	0	0
TOTAL ASSETS	2,815	2,726
CURRENT LIABILITIES
Short-term debt	41	94
Accounts and notes payable	610	700
Other current liabilities	285	290
TOTAL CURRENT LIABILITIES	936	1,084
LONG-TERM DEBT	902	730
RETIREMENT BENEFITS	336	262
INTERCOMPANY PAYABLE (RECEIVABLE)	0	0
OTHER LIABILITIES	226	332
MEZZANINE EQUITY	0	1
EQUITY ATTRIBUTABLE TO MERITOR, INC.	385	287
NONCONTROLLING INTERESTS	30	30
TOTAL LIABILITIES, MEZZANINE EQUITY AND EQUITY	2,815	2,726
Reportable Legal Entities | Parent
CURRENT ASSETS
Cash and cash equivalents	4	24
Receivables, trade and other, net	3	2
Inventories	0	0
Other current assets	6	6
TOTAL CURRENT ASSETS	13	32
NET PROPERTY	21	24
GOODWILL	0	0
OTHER ASSETS	170	179
INVESTMENTS IN SUBSIDIARIES	4,432	3,583
TOTAL ASSETS	4,636	3,818
CURRENT LIABILITIES
Short-term debt	32	47
Accounts and notes payable	53	64
Other current liabilities	77	77
TOTAL CURRENT LIABILITIES	162	188
LONG-TERM DEBT	898	726
RETIREMENT BENEFITS	312	241
INTERCOMPANY PAYABLE (RECEIVABLE)	2,833	2,325
OTHER LIABILITIES	46	50
MEZZANINE EQUITY	0	1
EQUITY ATTRIBUTABLE TO MERITOR, INC.	385	287
NONCONTROLLING INTERESTS	0	0
TOTAL LIABILITIES, MEZZANINE EQUITY AND EQUITY	4,636	3,818
Reportable Legal Entities | Guarantors
CURRENT ASSETS
Cash and cash equivalents	4	6
Receivables, trade and other, net	92	62
Inventories	292	242
Other current assets	10	12
TOTAL CURRENT ASSETS	398	322
NET PROPERTY	260	241
GOODWILL	337	250
OTHER ASSETS	225	182
INVESTMENTS IN SUBSIDIARIES	899	855
TOTAL ASSETS	2,119	1,850
CURRENT LIABILITIES
Short-term debt	0	0
Accounts and notes payable	283	297
Other current liabilities	109	71
TOTAL CURRENT LIABILITIES	392	368
LONG-TERM DEBT	0	0
RETIREMENT BENEFITS	1	0
INTERCOMPANY PAYABLE (RECEIVABLE)	(3,005)	(2,640)
OTHER LIABILITIES	112	124
MEZZANINE EQUITY	0	0
EQUITY ATTRIBUTABLE TO MERITOR, INC.	4,619	3,998
NONCONTROLLING INTERESTS	0	0
TOTAL LIABILITIES, MEZZANINE EQUITY AND EQUITY	2,119	1,850
Reportable Legal Entities | Non- Guarantors
CURRENT ASSETS
Cash and cash equivalents	100	85
Receivables, trade and other, net	456	524
Inventories	234	235
Other current assets	15	28
TOTAL CURRENT ASSETS	805	872
NET PROPERTY	234	218
GOODWILL	141	171
OTHER ASSETS	211	235
INVESTMENTS IN SUBSIDIARIES	0	0
TOTAL ASSETS	1,391	1,496
CURRENT LIABILITIES
Short-term debt	9	47
Accounts and notes payable	274	339
Other current liabilities	99	142
TOTAL CURRENT LIABILITIES	382	528
LONG-TERM DEBT	4	4
RETIREMENT BENEFITS	23	21
INTERCOMPANY PAYABLE (RECEIVABLE)	172	315
OTHER LIABILITIES	68	158
MEZZANINE EQUITY	0	0
EQUITY ATTRIBUTABLE TO MERITOR, INC.	712	440
NONCONTROLLING INTERESTS	30	30
TOTAL LIABILITIES, MEZZANINE EQUITY AND EQUITY	1,391	1,496
Elims
CURRENT ASSETS
Cash and cash equivalents	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	(5,331)	(4,438)
TOTAL ASSETS	(5,331)	(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.	(5,331)	(4,438)
NONCONTROLLING INTERESTS	0	0
TOTAL LIABILITIES, MEZZANINE EQUITY AND EQUITY	$ (5,331)	$ (4,438)