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SUPPLEMENTAL PARENT AND GUARANTOR CONDENSED CONSOLIDATING FINANCIAL STATEMENTS - Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Condensed Financial Statements, Captions [Line Items]
Net income	$ 238	$ 51	$ 23	$ 16	$ 474	$ 42	$ 32	$ 27	$ 328	$ 575	$ 65
Other comprehensive income (loss)									264	(43)	(19)
Total comprehensive income									592	532	46
Less: Comprehensive (income) loss attributable to noncontrolling interest									(4)	(2)	1
Comprehensive income attributable to Meritor, Inc.									588	530	47
Reportable Legal Entities \| Parent
Condensed Financial Statements, Captions [Line Items]
Net income									324	573	64
Other comprehensive income (loss)									264	(43)	(17)
Total comprehensive income									588	530	47
Less: Comprehensive (income) loss attributable to noncontrolling interest									0	0	0
Comprehensive income attributable to Meritor, Inc.									588	530	47
Reportable Legal Entities \| Guarantors
Condensed Financial Statements, Captions [Line Items]
Net income									495	243	269
Other comprehensive income (loss)									21	11	(77)
Total comprehensive income									516	254	192
Less: Comprehensive (income) loss attributable to noncontrolling interest									0	0	0
Comprehensive income attributable to Meritor, Inc.									516	254	192
Reportable Legal Entities \| Non- Guarantors
Condensed Financial Statements, Captions [Line Items]
Net income									124	138	43
Other comprehensive income (loss)									23	(44)	(18)
Total comprehensive income									147	94	25
Less: Comprehensive (income) loss attributable to noncontrolling interest									(4)	(2)	1
Comprehensive income attributable to Meritor, Inc.									143	92	26
Elims
Condensed Financial Statements, Captions [Line Items]
Net income									(615)	(379)	(311)
Other comprehensive income (loss)									(44)	33	93
Total comprehensive income									(659)	(346)	(218)
Less: Comprehensive (income) loss attributable to noncontrolling interest									0	0	0
Comprehensive income attributable to Meritor, Inc.									$ (659)	$ (346)	$ (218)