Business Segment Information - Segment Income Attributable to Parent (Details) - USD ($) $ in Millions			3 Months Ended	6 Months Ended
Mar. 13, 2020	Jan. 22, 2019	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Interest expense, net			$ (16)	$ (15)	$ (30)	$ (29)
Provision for income taxes			(73)	(27)	(86)	(48)
Depreciation and amortization					(50)	(43)
Noncontrolling interests			(1)	(2)	(3)	(4)
Restructuring					(15)	1
Income from WABCO distribution termination	$ 265		265	0	265	0
Asbestos related liability remeasurement					0	31
Income from continuing operations attributable to Meritor, Inc.			240	73	279	163
Maremont Asbestos
Segment Reporting Information [Line Items]
Asbestos related liability remeasurement		$ 31				31
Reportable Segments
Segment Reporting Information [Line Items]
Segment adjusted EBITDA			104	140	200	257
Reportable Segments \| Commercial Truck
Segment Reporting Information [Line Items]
Segment adjusted EBITDA			55	88	111	165
Reportable Segments \| Aftermarket, Industrial and Trailer
Segment Reporting Information [Line Items]
Segment adjusted EBITDA			49	52	89	92
Segment Reconciling Items
Segment Reporting Information [Line Items]
Unallocated legacy and corporate income, net			3	(1)	5	1
Interest expense, net			(16)	(15)	(30)	(29)
Provision for income taxes			(73)	(27)	(86)	(48)
Depreciation and amortization			(26)	(21)	(50)	(43)
Noncontrolling interests			(1)	(2)	(3)	(4)
Loss on sale of receivables			(1)	(2)	(2)	(3)
Restructuring			(10)	1	(15)	1
Transaction costs			(5)	0	(5)	0
Income from WABCO distribution termination			265	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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This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

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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 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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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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