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)	59			85		(33)	52	7
Equity based compensation expense	14		14				14
Vesting of equity based awards		1	(1)
Repurchase of common stock	(63)				(63)		(63)
Noncontrolling interest dividends	(1)							(1)
Other equity adjustments	(1)		1				1	(2)
Ending Balance at Jun. 30, 2018	303	102	779	168	(199)	(578)	272	31
Beginning balance at Mar. 31, 2018	312	102	775	104	(169)	(530)	282	30
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	17			64		(48)	16	1
Equity based compensation expense	4		4				4
Repurchase of common stock	(30)				(30)		(30)
Ending Balance at Jun. 30, 2018	303	102	779	168	(199)	(578)	272	31
Beginning balance at Sep. 30, 2018	317	102	787	200	(236)	(566)	287	30
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	252			248		(3)	245	7
Equity based compensation expense	13		13				13
Vesting of equity based awards		2	(2)
Repurchase of common stock	(71)				(71)		(71)
Noncontrolling interest dividends	(1)							(1)
Ending Balance at Jun. 30, 2019	510	104	798	448	(307)	(569)	474	36
Beginning balance at Mar. 31, 2019	445	104	793	362	(286)	(562)	411	34
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	81			86		(7)	79	2
Equity based compensation expense	5		5				5
Repurchase of common stock	(21)				(21)		(21)
Ending Balance at Jun. 30, 2019	$ 510	$ 104	$ 798	$ 448	$ (307)	$ (569)	$ 474	$ 36