Retirement Benefit Liabilities - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Retirement Benefits [Abstract]
Non-service cost components of the net periodic pension and OPEB income	$ 9	$ 7	$ 28	$ 23

Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income

No definition available.

Name:	mtor_DefinedBenefitPlanNetPeriodicBenefitCostCreditExcludingServiceCostStatementOfIncomeOrComprehensiveIncome
Namespace Prefix:	mtor_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration