CONDENSED CONSOLIDATED STATEMENT OF EQUITY - USD ($) $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Additional Paid-in Capital	Additional Paid-in Capital Cumulative Effect, Period of Adoption, Adjustment	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Treasury Stock	Accumulated Other Comprehensive Loss	Total Equity Attributable to Meritor, Inc.	Total Equity Attributable to Meritor, Inc. Cumulative Effect, Period of Adoption, Adjustment	Noncontrolling Interests
Beginning balance at Sep. 30, 2020	$ 495		$ 105	$ 808		$ 736		$ (573)	$ (614)	$ 462		$ 33
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	138					95			39	134		4
Repurchase of convertible notes	(30)			(30)						(30)
Equity based compensation expense	10			10						10
Vesting of equity based awards	0		1	(1)
Noncontrolling interest dividends	(1)											(1)
Other equity adjustments	1			1						1
Ending Balance at Mar. 31, 2021	613		106	788		831		(573)	(575)	577		36
Beginning balance at Sep. 30, 2020	495		105	808		736		(573)	(614)	462		33
Ending Balance at Sep. 30, 2021	$ 615	$ (23)	105	798	$ (40)	935	$ 17	(632)	(632)	574	$ (23)	41
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible Enumeration]	Accounting Standards Update 2020-06
Beginning balance at Dec. 31, 2020	$ 565		106	784		768		(573)	(555)	530		35
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	45					63			(20)	43		2
Equity based compensation expense	4			4						4
Noncontrolling interest dividends	(1)											(1)
Ending Balance at Mar. 31, 2021	613		106	788		831		(573)	(575)	577		36
Beginning balance at Sep. 30, 2021	615	$ (23)	105	798	$ (40)	935	$ 17	(632)	(632)	574	$ (23)	41
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	127					116			4	120		7
Equity based compensation expense	8			8						8
Vesting of equity based awards	0		1	(1)
Noncontrolling interest dividends	(7)											(7)
Ending Balance at Mar. 31, 2022	720		106	765		1,068		(632)	(628)	679		41
Beginning balance at Dec. 31, 2021	638		106	761		1,006		(632)	(644)	597		41
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	81					62			16	78		3
Equity based compensation expense	4			4						4
Noncontrolling interest dividends	(3)											(3)
Ending Balance at Mar. 31, 2022	$ 720		$ 106	$ 765		$ 1,068		$ (632)	$ (628)	$ 679		$ 41