CONDENSED CONSOLIDATED STATEMENT OF EQUITY - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Loss	Total Equity Attributable to Meritor, Inc.	Noncontrolling Interests
Beginning balance at Sep. 30, 2018	$ 317	$ 102	$ 787	$ 200	$ (236)	$ (566)	$ 287	$ 30
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	90			90		(3)	87	3
Equity based compensation expense	5		5				5
Vesting of equity based awards	0	2	(2)
Repurchase of common stock	(50)				(50)		(50)
Ending Balance at Dec. 31, 2018	362	104	790	290	(286)	(569)	329	33
Beginning balance at Sep. 30, 2019	415	104	803	491	(332)	(681)	385	30
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	67			39		26	65	2
Equity based compensation expense	3		3				3
Vesting of equity based awards	0	1	(1)
Repurchase of common stock	(100)				(100)		(100)
Other equity adjustments	(1)		(1)				(1)
Ending Balance at Dec. 31, 2019	$ 384	$ 105	$ 804	$ 530	$ (432)	$ (655)	$ 352	$ 32