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, 2017	$ 295	$ 101	$ 765	$ 83	$ (136)	$ (545)	$ 268	$ 27
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	(38)			(36)		(5)	(41)	3
Equity based compensation expense	5		5				5
Vesting of equity based awards		1	(1)
Other equity adjustments	1		1				1
Ending Balance at Dec. 31, 2017	263	102	770	47	(136)	(550)	233	30
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		2	(2)
Repurchase of common stock	(50)				(50)		(50)
Ending Balance at Dec. 31, 2018	$ 362	$ 104	$ 790	$ 290	$ (286)	$ (569)	$ 329	$ 33