Acquisition - Pro Forma Financial Information (Details) - TransPower - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Business Acquisition [Line Items]
Sales	$ 514	$ 1,168	$ 2,287	$ 3,364
Net income attributable to Meritor, Inc.	$ (36)	$ 83	$ 243	$ 242