Retirement Benefit Liabilities - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Retirement Benefits [Abstract]
Non-service cost components of the net periodic pension and OPEB income	$ 13	$ 11	$ 26	$ 21

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