Business Segment Information - Segment Income Attributable to Parent (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Interest expense, net	$ (14)		$ (14)	$ (43)	$ (54)
Provision for income taxes	(21)		(26)	(69)	(131)
Depreciation and amortization				(64)	(64)
Noncontrolling interests	(3)		(3)	(7)	(8)
Asset impairment charges				(1)	(2)
Restructuring	1		(3)	2	(6)
Asbestos related liability remeasurement				31	0
Income from continuing operations attributable to Meritor, Inc.	85		66	248	88
Operating Segments
Segment Reporting Information [Line Items]
Segment adjusted EBITDA	147		138	404	371
Operating Segments \| Commercial Truck
Segment Reporting Information [Line Items]
Segment adjusted EBITDA	93		100	258	263
Operating Segments \| Aftermarket, Industrial and Trailer
Segment Reporting Information [Line Items]
Segment adjusted EBITDA	54		38	146	108
Segment Reconciling Items
Segment Reporting Information [Line Items]
Unallocated legacy and corporate income, net	(1)		(3)	0	(15)
Interest expense, net	(14)		(14)	(43)	(54)
Provision for income taxes	(21)		(26)	(69)	(131)
Depreciation and amortization	(21)		(22)	(64)	(64)
Noncontrolling interests	(3)		(3)	(7)	(8)
Loss on sale of receivables	(2)		(1)	(5)	(3)
Asset impairment charges	(1)		0	(1)	(2)
Restructuring	1		(3)	2	(6)
Asbestos related liability remeasurement	$ 0		$ 0	31	$ 0
Maremont Asbestos
Segment Reporting Information [Line Items]
Asbestos related liability remeasurement		$ 31		$ 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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Segment EBITDA is defined as income (loss) from continuing operations before interest expense, income taxes, depreciation and amortization, non-controlling interests in consolidated joint ventures, loss on sale of receivables, restructuring expenses and asset impairment charges.

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Unallocated legacy and corporate costs represent items that are not directly related to our business segments and include pension and retiree medical costs associated with sold businesses and other legacy costs for environmental and product liability matters.

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The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

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Amount of gain (loss) on sale of accounts receivable.

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Amount after tax of income (loss) from continuing operations attributable to the parent.

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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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Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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