Business Segment Information - Segment Income Attributable to Parent (Details) - USD ($) $ in Millions			3 Months Ended	9 Months Ended
Mar. 13, 2020	Jan. 22, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Interest expense, net			$ (17)	$ (14)	$ (47)	$ (43)
Benefit (provision) for income taxes			13	(21)	(73)	(69)
Depreciation and amortization					(74)	(64)
Noncontrolling interests			(2)	(3)	(5)	(7)
Asset impairment charges					0	(1)
Restructuring					(27)	2
Income from WABCO distribution termination	$ 265		0	0	265	0
Asbestos related liability remeasurement					0	31
Income (loss) from continuing operations attributable to Meritor, Inc.			(36)	85	243	248
Maremont Asbestos
Segment Reporting Information [Line Items]
Asbestos related liability remeasurement		$ 31				31
Reportable Segments
Segment Reporting Information [Line Items]
Segment adjusted EBITDA			8	147	208	404
Reportable Segments \| Commercial Truck
Segment Reporting Information [Line Items]
Segment adjusted EBITDA			(23)	97	92	270
Reportable Segments \| Aftermarket and Industrial
Segment Reporting Information [Line Items]
Segment adjusted EBITDA			31	50	116	134
Segment Reconciling Items
Segment Reporting Information [Line Items]
Unallocated legacy and corporate income, net			(1)	(1)	4	0
Interest expense, net			(17)	(14)	(47)	(43)
Benefit (provision) for income taxes			13	(21)	(73)	(69)
Depreciation and amortization			(24)	(21)	(74)	(64)
Noncontrolling interests			(2)	(3)	(5)	(7)
Loss on sale of receivables			(1)	(2)	(3)	(5)
Asset impairment charges			0	(1)	0	(1)
Restructuring			(12)	1	(27)	2
Transaction costs			0	0	(5)	0
Income from WABCO distribution termination			0	0	265	0
Asbestos related liability remeasurement			$ 0	$ 0	$ 0	$ 31

Asbestos Related Liability Remeasurement Gain (Loss)

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Gain (Loss) From Termination Of Purchase And Option Agreement

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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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Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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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 Net Income (Loss) attributable to noncontrolling interest.

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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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