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, 2019	$ 415	$ 104	$ 803	$ 491	$ (332)	$ (681)	$ 385	$ 30
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	250			280		(33)	247	3
Equity based compensation expense	1		1				1
Vesting of equity based awards	0	1	(1)
Repurchase of common stock	(241)				(241)		(241)
Noncontrolling interest dividend	(1)							(1)
Ending Balance at Mar. 31, 2020	424	105	803	771	(573)	(714)	392	32
Beginning balance at Dec. 31, 2019	384	105	804	530	(432)	(655)	352	32
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	183			241		(59)	182	1
Equity based compensation expense	(2)		(2)				(2)
Repurchase of common stock	(141)				(141)		(141)
Noncontrolling interest dividend	(1)							(1)
Other equity adjustments	1		1				1
Ending Balance at Mar. 31, 2020	424	105	803	771	(573)	(714)	392	32
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
Equity based compensation expense	10		10				10
Vesting of equity based awards	0	1	(1)
Repurchase of convertible notes	(30)		(30)				(30)
Noncontrolling interest dividend	(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 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 dividend	(1)							(1)
Ending Balance at Mar. 31, 2021	$ 613	$ 106	$ 788	$ 831	$ (573)	$ (575)	$ 577	$ 36