Supplemental Guarantor Condensed Consolidating Financial Statements - Condensed Consolidating Balance Sheet (Details) - USD ($) $ in Millions		Jun. 30, 2018		Sep. 30, 2017		Jun. 30, 2017	Sep. 30, 2016
CURRENT ASSETS:
Cash and cash equivalents		$ 100	[1]	$ 88	[1]	$ 231	$ 160
Receivables trade and other, net	[1]	609		789
Inventories	[1]	466		378
Other current assets		36		43
TOTAL CURRENT ASSETS		1,211		1,298
NET PROPERTY	[1]	447		474
GOODWILL	[1]	419		414
OTHER ASSETS	[1]	539		596
INVESTMENTS IN SUBSIDIARIES		0		0
TOTAL ASSETS		2,616		2,782
CURRENT LIABILITIES:
Short-term debt		48		288
Accounts and notes payable	[1]	731		622
Other current liabilities		278		272
TOTAL CURRENT LIABILITIES		1,057		1,182
LONG-TERM DEBT		728		750
RETIREMENT BENEFITS		282		314
INTERCOMPANY PAYABLE (RECEIVABLE)		0		0
OTHER LIABILITIES		244		239
MEZZANINE EQUITY		2		2
EQUITY ATTRIBUTABLE TO MERITOR, INC.		272		268
NONCONTROLLING INTERESTS	[1]	31		27
TOTAL LIABILITIES, MEZZANINE EQUITY AND EQUITY		2,616		2,782
ASSETS, LIABILITIES, AND EQUITY HELD-FOR-SALE
Cash and cash equivalents				1
Receivables, trade and other, net				13
Inventories				2
Net property		1		3
Goodwill				1
Other assets				1
Accounts and notes payable				12
Noncontrolling interests				2
Elims
CURRENT ASSETS:
Cash and cash equivalents		0		0		0	0
Receivables trade and other, net		0		0
Inventories		0		0
Other current assets		0		0
TOTAL CURRENT ASSETS		0		0
NET PROPERTY		0		0
GOODWILL		0		0
OTHER ASSETS		0		0
INVESTMENTS IN SUBSIDIARIES		(4,354)		(4,009)
TOTAL ASSETS		(4,354)		(4,009)
CURRENT LIABILITIES:
Short-term debt		0		0
Accounts and notes payable		0		0
Other current liabilities		0		0
TOTAL CURRENT LIABILITIES		0		0
LONG-TERM DEBT		0		0
RETIREMENT BENEFITS		0		0
INTERCOMPANY PAYABLE (RECEIVABLE)		0		0
OTHER LIABILITIES		0		0
MEZZANINE EQUITY		0		0
EQUITY ATTRIBUTABLE TO MERITOR, INC.		(4,354)		(4,009)
NONCONTROLLING INTERESTS		0		0
TOTAL LIABILITIES, MEZZANINE EQUITY AND EQUITY		(4,354)		(4,009)
Parent | Reportable Legal Entities
CURRENT ASSETS:
Cash and cash equivalents		15		10		150	90
Receivables trade and other, net		3		0
Inventories		0		0
Other current assets		1		5
TOTAL CURRENT ASSETS		19		15
NET PROPERTY		20		21
GOODWILL		0		0
OTHER ASSETS		186		271
INVESTMENTS IN SUBSIDIARIES		3,496		3,222
TOTAL ASSETS		3,721		3,529
CURRENT LIABILITIES:
Short-term debt		47		195
Accounts and notes payable		56		55
Other current liabilities		97		69
TOTAL CURRENT LIABILITIES		200		319
LONG-TERM DEBT		724		743
RETIREMENT BENEFITS		261		291
INTERCOMPANY PAYABLE (RECEIVABLE)		2,217		1,866
OTHER LIABILITIES		45		40
MEZZANINE EQUITY		2		2
EQUITY ATTRIBUTABLE TO MERITOR, INC.		272		268
NONCONTROLLING INTERESTS		0		0
TOTAL LIABILITIES, MEZZANINE EQUITY AND EQUITY		3,721		3,529
Guarantors | Reportable Legal Entities
CURRENT ASSETS:
Cash and cash equivalents		7		3		4	4
Receivables trade and other, net		55		296
Inventories		226		184
Other current assets		6		6
TOTAL CURRENT ASSETS		294		489
NET PROPERTY		225		227
GOODWILL		249		237
OTHER ASSETS		136		106
INVESTMENTS IN SUBSIDIARIES		858		787
TOTAL ASSETS		1,762		1,846
CURRENT LIABILITIES:
Short-term debt		1		2
Accounts and notes payable		289		246
Other current liabilities		54		69
TOTAL CURRENT LIABILITIES		344		317
LONG-TERM DEBT		0		0
RETIREMENT BENEFITS		0		0
INTERCOMPANY PAYABLE (RECEIVABLE)		(2,555)		(2,160)
OTHER LIABILITIES		90		93
MEZZANINE EQUITY		0		0
EQUITY ATTRIBUTABLE TO MERITOR, INC.		3,883		3,596
NONCONTROLLING INTERESTS		0		0
TOTAL LIABILITIES, MEZZANINE EQUITY AND EQUITY		1,762		1,846
ASSETS, LIABILITIES, AND EQUITY HELD-FOR-SALE
Net property				1
Non- Guarantors | Reportable Legal Entities
CURRENT ASSETS:
Cash and cash equivalents		78		75		$ 77	$ 66
Receivables trade and other, net		551		493
Inventories		240		194
Other current assets		29		32
TOTAL CURRENT ASSETS		898		794
NET PROPERTY		202		226
GOODWILL		170		177
OTHER ASSETS		217		219
INVESTMENTS IN SUBSIDIARIES		0		0
TOTAL ASSETS		1,487		1,416
CURRENT LIABILITIES:
Short-term debt		0		91
Accounts and notes payable		386		321
Other current liabilities		127		134
TOTAL CURRENT LIABILITIES		513		546
LONG-TERM DEBT		4		7
RETIREMENT BENEFITS		21		23
INTERCOMPANY PAYABLE (RECEIVABLE)		338		294
OTHER LIABILITIES		109		106
MEZZANINE EQUITY		0		0
EQUITY ATTRIBUTABLE TO MERITOR, INC.		471		413
NONCONTROLLING INTERESTS		31		27
TOTAL LIABILITIES, MEZZANINE EQUITY AND EQUITY		$ 1,487		$ 1,416

[1] As of June 30, 2018, Assets and liabilities held for sale consisted of $1 million Net property. As of September 30, 2017, Assets and liabilities held for sale were: (i) $1 million Cash and cash equivalents; (ii) $13 million Receivables, trade and other, net; (iii) $2 million Inventories; (iv) $3 million Net property; (v) $1 million Goodwill; (vi) $1 million Other assets; (vii) $12 million Accounts and notes payable; and (viii) $2 million Noncontrolling interests.