Basis of Presentation (Policies)	9 Months Ended
Basis of Presentation (Policies)	Jun. 30, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
New Accounting Standards	Accounting standards to be implemented In April 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2014-08, Presentation of Financial Statements and Property, Plant, and Equipment: Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity. ASU 2014-08 changes the criteria for determining which disposals can be presented as discontinued operations and modifies related disclosure requirements. Under the new guidance, a discontinued operation is defined as a disposal of a component or group of components that represents a strategic shift that has (or will have) a major effect on an entity's operations and financial results. A strategic shift could include a disposal of: (1) a major geographical area of operations; (2) a major line of business; and (3) a major equity method investment. The standard is required to be adopted by public business entities in annual periods beginning on or after December 15, 2014, and interim periods within those annual periods. The company plans to implement this standard in the first quarter of the fiscal year beginning October 1, 2015. The potential impact of this new guidance on its consolidated financial statements is dependent upon future business divestitures. Previous divestitures and amounts currently in discontinued operations will not be impacted. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers. ASU 2014-09 merges revenue recognition standards of the FASB and International Accounting Standards Board (IASB). The FASB and IASB initiated a joint project to clarify the principles for recognizing revenue and to develop a common revenue standard for U.S. GAAP and International Financial Reporting Standards (IFRS) that would: (1) remove inconsistencies and weaknesses in revenue requirements; (2) provide a more robust framework for addressing revenue issues; (3) improve comparability of revenue recognition practices across entities, industries, jurisdictions, and capital markets; (4) provide more useful information to users of financial statements through improved disclosure requirements; and (5) simplify the preparation of financial statements by reducing the number of requirements to which an entity must refer. The standard is required to be adopted by public business entities in annual periods beginning after December 15, 2017 and interim periods within those annual periods. The company plans to implement this standard in the first quarter of the fiscal year beginning October 1, 2018 and is currently evaluating the potential impact of this new guidance on its consolidated financial statements. In June 2014, the FASB issued ASU 2014-12, Compensation—Stock Compensation (Topic 718): Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period. ASU 2014-12 applies to all reporting entities that grant their employees share-based payments in which the terms of the award provide that a performance target that affects vesting could be achieved after the requisite service period. That is the case when an employee is eligible to retire or otherwise terminate employment before the end of the period in which a performance target (for example, an initial public offering or a profitability target) could be achieved and still be eligible to vest in the award if and when the performance target is achieved. The standard is required to be adopted by public business entities in annual periods beginning on or after December 15, 2015 and interim periods within those annual periods. The company plans to implement this standard in the first quarter of the fiscal year beginning on October 1, 2016 and is currently evaluating the potential impact of this new guidance on its consolidated financial statements. In August 2014, the FASB issued ASU 2014-15, Presentation of Financial Statements — Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern. ASU 2014-15 requires management to assess an entity’s ability to continue as a going concern by incorporating and expanding upon certain principles that are currently in U.S. auditing standards. Specifically, ASU 2014-15 (1) provides a definition of the term substantial doubt, (2) requires an evaluation every reporting period including interim periods, (3) provides principles for considering the mitigating effect of management’s plans, (4) requires certain disclosures when substantial doubt is alleviated as a result of consideration of management’s plans, (5) requires an express statement and other disclosures when substantial doubt is not alleviated, and (6) requires an assessment for a period of one year after the date that the financial statements are issued (or are available to be issued). The standard is required to be adopted by public business entities in annual periods ending after December 15, 2016, and for annual periods and interim periods thereafter. Early application is permitted. The company plans to implement this standard in the fiscal year beginning October 1, 2016 and currently expects this new guidance to have no impact on the company’s consolidated financial statements. In April 2015, the FASB issued ASU 2015-03, Interest — Imputation of Interest (Subtopic 835-30): Simplifying the Presentation of Debt Issuance Costs. ASU 2015-03 changes the presentation of debt issuance costs for term debt in the balance sheet by requiring the debt issuance costs to be presented as a direct deduction from the related debt liability, rather than recorded as an asset. The standard is required to be adopted by public business entities in annual periods beginning on or after December 15, 2015, and interim periods within those annual periods and will need to be applied retrospectively. Early adoption is permitted. The company plans to implement this standard in the fourth quarter of fiscal year 2015. Debt issuance costs associated with term debt as of June 30, 2015 and September 30, 2014, were $18 million and $17 million, respectively. Accounting standards implemented during fiscal year 2015 In April 2015, the FASB issued ASU 2015-05, Intangibles — Goodwill and Other — Internal-Use Software. ASU 2015-05 requires a company to determine whether a cloud computing arrangement contains a software license. If the arrangement contains a software license, the customer would account for the fees related to the software license element in a manner consistent with how the acquisition of other software licenses is accounted for under ASC 350-40; if the arrangement does not contain a software license, the customer would account for the arrangement as a service contract. The standard is required to be adopted by public business entities in annual periods beginning after December 15, 2015, and interim periods within those annual periods. Early adoption is permitted. The company adopted this guidance concurrent with an annual review of the company's accounting for internal-use computer software costs policy. The new accounting standard will be applied prospectively. The adoption did not have a material impact on the company's consolidated statement of financial position, results of operations, or cash flows. As new contracts are entered into or existing contracts are materially modified, the adoption may impact fixed assets, selling, general and administrative costs, or cost of sales.
Inventory	Inventories are stated at the lower of cost (using FIFO or average methods) or market (determined on the basis of estimated realizable values)
Environmental costs	Federal, state and local requirements relating to the discharge of substances into the environment, the disposal of hazardous wastes and other activities affecting the environment have, and will continue to have, an impact on the operations of the company. The process of estimating environmental liabilities is complex and dependent upon evolving physical and scientific data at the sites, uncertainties as to remedies and technologies to be used and the outcome of discussions with regulatory agencies. The company records liabilities for environmental issues in the accounting period in which they are considered to be probable and the cost can be reasonably estimated. At environmental sites in which more than one potentially responsible party has been identified, the company records a liability for its allocable share of costs related to its involvement with the site, as well as an allocable share of costs related to insolvent parties or unidentified shares. At environmental sites in which Meritor is the only potentially responsible party, the company records a liability for the total probable and estimable costs of remediation before consideration of recovery from insurers or other third parties.

Disclosure of accounting policy for major classes of inventories, bases of stating inventories (for example, lower of cost or market), methods by which amounts are added and removed from inventory classes (for example, FIFO, LIFO, or average cost), loss recognition on impairment of inventories, and situations in which inventories are stated above cost. If inventory is carried at cost, this disclosure includes the nature of the cost elements included in inventory.