Business Segment Information - Segment Income Attributable to Parent (Details) - USD ($) $ in Millions	3 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Interest expense, net	$ (14)	$ (24)
Provision for income taxes	(21)	(83)
Depreciation and amortization	(22)	(21)
Noncontrolling interests	(2)	(2)
Restructuring costs	0	(2)
Asbestos related liability remeasurement	31	0
Income (loss) from continuing operations attributable to Meritor, Inc.	90	(35)
Operating Segments
Segment Reporting Information [Line Items]
Segment adjusted EBITDA	117	101
Operating Segments \| Commercial Truck & Trailer
Segment Reporting Information [Line Items]
Segment adjusted EBITDA	79	69
Operating Segments \| Aftermarket & Industrial
Segment Reporting Information [Line Items]
Segment adjusted EBITDA	38	32
Segment Reconciling Items
Segment Reporting Information [Line Items]
Unallocated legacy and corporate income, net	2	(2)
Interest expense, net	(14)	(24)
Provision for income taxes	(21)	(83)
Depreciation and amortization	(22)	(21)
Noncontrolling interests	(2)	(2)
Loss on sale of receivables	(1)	(2)
Restructuring costs	0	(2)
Asbestos related liability remeasurement	31	$ 0
Maremont Asbestos
Segment Reporting Information [Line Items]
Asbestos related liability remeasurement	$ 31

Asbestos Related Liability Remeasurement Gain (Loss)

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Interest expense incurred and charged against earnings during the reporting period on all debt, including interest on short-term obligations and long-term debt, and amortization of issuance costs and debt discounts, etc. Interest expense is net of interest income earned during the reporting period.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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