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)	252			248		(3)	245	7
Equity based compensation expense	13		13				13
Vesting of equity based awards	0	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
Beginning balance at Sep. 30, 2019	415	104	803	491	(332)	(681)	385	30
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	227			244		(20)	224	3
Equity based compensation expense	3		3				3
Vesting of equity based awards	0	1	(1)
Repurchase of common stock	(241)				(241)		(241)
Noncontrolling interest dividends	(1)							(1)
Ending Balance at Jun. 30, 2020	403	105	805	735	(573)	(701)	371	32
Beginning balance at Mar. 31, 2020	424	105	803	771	(573)	(714)	392	32
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	(23)			(36)		13	(23)	0
Equity based compensation expense	2		2				2
Ending Balance at Jun. 30, 2020	$ 403	$ 105	$ 805	$ 735	$ (573)	$ (701)	$ 371	$ 32