Supplemental Guarantor Condensed Consolidating Financial Statements - Condensed Consolidating Balance Sheet (Details) - USD ($) $ in Millions		Dec. 31, 2017		Sep. 30, 2017		Dec. 31, 2016	Sep. 30, 2016
CURRENT ASSETS:
Cash and cash equivalents		$ 116	[1]	$ 88	[1]	$ 125	$ 160
Receivables trade and other, net	[1]	456		789
Inventories	[1]	427		378
Other current assets		43		43
TOTAL CURRENT ASSETS		1,042		1,298
NET PROPERTY	[1]	464		474
GOODWILL	[1]	414		414
OTHER ASSETS	[1]	525		596
INVESTMENTS IN SUBSIDIARIES		0		0
TOTAL ASSETS		2,445		2,782
CURRENT LIABILITIES:
Short-term debt		63		288
Accounts and notes payable	[1]	592		622
Other current liabilities		238		272
TOTAL CURRENT LIABILITIES		893		1,182
LONG-TERM DEBT		751		750
RETIREMENT BENEFITS		298		314
INTERCOMPANY PAYABLE (RECEIVABLE)		0		0
OTHER LIABILITIES		238		239
MEZZANINE EQUITY		2		2
EQUITY (DEFICIT) ATTRIBUTABLE TO MERITOR, INC.		233		268
NONCONTROLLING INTERESTS	[1]	30		27
TOTAL LIABILITIES, MEZZANINE EQUITY AND EQUITY (DEFICIT)		2,445		2,782
ASSETS, LIABILITIES, AND EQUITY HELD-FOR-SALE
Cash and cash equivalents		3		1
Receivables, trade and other, net		14		13
Inventories		2		2
Net property		3		3
Goodwill		1		1
Other assets		1		1
Accounts and notes payable		15		12
Noncontrolling interests		2		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		(4,150)		(4,009)
TOTAL ASSETS		(4,150)		(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 (DEFICIT) ATTRIBUTABLE TO MERITOR, INC.		(4,150)		(4,009)
NONCONTROLLING INTERESTS		0		0
TOTAL LIABILITIES, MEZZANINE EQUITY AND EQUITY (DEFICIT)		(4,150)		(4,009)
Parent | Reportable Legal Entities
CURRENT ASSETS:
Cash and cash equivalents		23		10		65	90
Receivables trade and other, net		1		0
Inventories		0		0
Other current assets		6		5
TOTAL CURRENT ASSETS		30		15
NET PROPERTY		21		21
GOODWILL		0		0
OTHER ASSETS		195		271
INVESTMENTS IN SUBSIDIARIES		3,327		3,222
TOTAL ASSETS		3,573		3,529
CURRENT LIABILITIES:
Short-term debt		22		195
Accounts and notes payable		18		55
Other current liabilities		62		69
TOTAL CURRENT LIABILITIES		102		319
LONG-TERM DEBT		744		743
RETIREMENT BENEFITS		276		291
INTERCOMPANY PAYABLE (RECEIVABLE)		2,178		1,866
OTHER LIABILITIES		38		40
MEZZANINE EQUITY		2		2
EQUITY (DEFICIT) ATTRIBUTABLE TO MERITOR, INC.		233		268
NONCONTROLLING INTERESTS		0		0
TOTAL LIABILITIES, MEZZANINE EQUITY AND EQUITY (DEFICIT)		3,573		3,529
Guarantors | Reportable Legal Entities
CURRENT ASSETS:
Cash and cash equivalents		3		3		4	4
Receivables trade and other, net		37		296
Inventories		204		184
Other current assets		7		6
TOTAL CURRENT ASSETS		251		489
NET PROPERTY		223		227
GOODWILL		236		237
OTHER ASSETS		113		106
INVESTMENTS IN SUBSIDIARIES		823		787
TOTAL ASSETS		1,646		1,846
CURRENT LIABILITIES:
Short-term debt		2		2
Accounts and notes payable		236		246
Other current liabilities		54		69
TOTAL CURRENT LIABILITIES		292		317
LONG-TERM DEBT		0		0
RETIREMENT BENEFITS		0		0
INTERCOMPANY PAYABLE (RECEIVABLE)		(2,437)		(2,160)
OTHER LIABILITIES		92		93
MEZZANINE EQUITY		0		0
EQUITY (DEFICIT) ATTRIBUTABLE TO MERITOR, INC.		3,699		3,596
NONCONTROLLING INTERESTS		0		0
TOTAL LIABILITIES, MEZZANINE EQUITY AND EQUITY (DEFICIT)		1,646		1,846
ASSETS, LIABILITIES, AND EQUITY HELD-FOR-SALE
Net property		1		1
Non- Guarantors | Reportable Legal Entities
CURRENT ASSETS:
Cash and cash equivalents		90		75		$ 56	$ 66
Receivables trade and other, net		418		493
Inventories		223		194
Other current assets		30		32
TOTAL CURRENT ASSETS		761		794
NET PROPERTY		220		226
GOODWILL		178		177
OTHER ASSETS		217		219
INVESTMENTS IN SUBSIDIARIES		0		0
TOTAL ASSETS		1,376		1,416
CURRENT LIABILITIES:
Short-term debt		39		91
Accounts and notes payable		338		321
Other current liabilities		122		134
TOTAL CURRENT LIABILITIES		499		546
LONG-TERM DEBT		7		7
RETIREMENT BENEFITS		22		23
INTERCOMPANY PAYABLE (RECEIVABLE)		259		294
OTHER LIABILITIES		108		106
MEZZANINE EQUITY		0		0
EQUITY (DEFICIT) ATTRIBUTABLE TO MERITOR, INC.		451		413
NONCONTROLLING INTERESTS		30		27
TOTAL LIABILITIES, MEZZANINE EQUITY AND EQUITY (DEFICIT)		$ 1,376		$ 1,416

[1] As of December 31, 2017, Assets and liabilities held for sale were: (i) $3 million Cash and cash equivalents; (ii) $14 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) $15 million Accounts and notes payable; and (viii) $2 million Noncontrolling interests. 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.