Significant Restructuring and Impairment Costs (Detail) $ in Millions	12 Months Ended			36 Months Ended
	Sep. 30, 2018 USD ($) Plant Employees	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2018 USD ($) Plant Employees
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	$ 263	$ 367	$ 288
Restructuring Reserve			445
Number of employees to be severed \| Employees				11,500
Restructuring and Related Cost, Number of Positions Eliminated, Inception to Date \| Employees	4,900			4,900
Restructuring And Related Cost Expected Number Of Plants To Be Closed \| Plant	12
Number Of Plants Closed \| Plant	7			7
Power Solutions
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	$ 8	20	66
Number of employees to be severed \| Employees				200
Building Technologies & Solutions
Restructuring Cost and Reserve [Line Items]
Number of employees to be severed \| Employees				9,100
Restructuring And Related Cost Expected Number Of Plants To Be Closed \| Plant	12
Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	$ 50	166	161
Number of employees to be severed \| Employees				2,200
Adient
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			332
2018 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	263
Payments for Restructuring	(47)
Restructuring Reserve, Settled without Cash	(42)
Restructuring Reserve	174			$ 174
2018 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	263
2018 Restructuring Plan [Member] \| Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	209
Payments for Restructuring	(45)
Restructuring Reserve, Settled without Cash	0
Restructuring Reserve	164			164
2018 Restructuring Plan [Member] \| Fixed Asset Impairment
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	42
Payments for Restructuring	0
Restructuring Reserve, Settled without Cash	(42)
Restructuring Reserve	0			0
2018 Restructuring Plan [Member] \| Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	12
Payments for Restructuring	(2)
Restructuring Reserve, Settled without Cash	0
Restructuring Reserve	10			10
2017 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		367
Payments for Restructuring	(158)	(75)
Restructuring Reserve, Settled without Cash	(1)	(78)
Adjustment to restructuring reserves		25
Restructuring Reserve	80	239		80
2017 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		367
2017 Restructuring Plan [Member] \| Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		276
Payments for Restructuring	(152)	(75)
Restructuring Reserve, Settled without Cash	0	0
Adjustment to restructuring reserves		25
Restructuring Reserve	74	226		74
2017 Restructuring Plan [Member] \| Fixed Asset Impairment
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		77
Payments for Restructuring	0	0
Restructuring Reserve, Settled without Cash	0	(77)
Adjustment to restructuring reserves		0
Restructuring Reserve	0	0		0
2017 Restructuring Plan [Member] \| Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		14
Payments for Restructuring	(6)	0
Restructuring Reserve, Settled without Cash	0	(1)
Adjustment to restructuring reserves		0
Restructuring Reserve	7	13		7
2017 Restructuring Plan [Member] \| Currency Translation
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		0
Payments for Restructuring	0	0
Restructuring Reserve, Settled without Cash	(1)	0
Adjustment to restructuring reserves		0
Restructuring Reserve	(1)	0		(1)
2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			620
Payments for Restructuring	(19)	(88)	(32)
Restructuring Reserve, Settled without Cash		1	(221)
Adjustment to restructuring reserves		(25)
Restructuring Reserve	73	92		73
2016 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			288
2016 Restructuring Plan [Member] \| Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			368
Payments for Restructuring	(17)	(86)	(32)
Restructuring Reserve, Settled without Cash		0	0
Adjustment to restructuring reserves		(25)
Restructuring Reserve	67	84	414	67
2016 Restructuring Plan [Member] \| Fixed Asset Impairment
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			190
Payments for Restructuring	0	0	0
Restructuring Reserve, Settled without Cash		0	(190)
Adjustment to restructuring reserves		0
Restructuring Reserve	0	0	0	0
2016 Restructuring Plan [Member] \| Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			62
Payments for Restructuring	(2)	(2)	0
Restructuring Reserve, Settled without Cash		0	(32)
Adjustment to restructuring reserves		0
Restructuring Reserve	4	6	30	4
2016 Restructuring Plan [Member] \| Currency Translation
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			0
Payments for Restructuring	0	0	0
Restructuring Reserve, Settled without Cash		1	1
Adjustment to restructuring reserves		0
Restructuring Reserve	2	2	1	$ 2
2016 Restructuring Plan [Member] \| Adient \| Discontinued Operations
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			332
2016 Restructuring Plan [Member] \| Adient spin-off [Member] \| Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash		(216)
2016 Restructuring Plan [Member] \| Adient spin-off [Member] \| Employee Severance \| Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash		(194)
2016 Restructuring Plan [Member] \| Adient spin-off [Member] \| Fixed Asset Impairment \| Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash		0
2016 Restructuring Plan [Member] \| Adient spin-off [Member] \| Other Restructuring [Member] \| Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash		(22)
2016 Restructuring Plan [Member] \| Adient spin-off [Member] \| Currency Translation \| Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash		0
2016 Restructuring Plan [Member] \| Scott Safety business [Member] \| Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash		(3)
2016 Restructuring Plan [Member] \| Scott Safety business [Member] \| Employee Severance \| Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash		(3)
2016 Restructuring Plan [Member] \| Scott Safety business [Member] \| Fixed Asset Impairment \| Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash		0
2016 Restructuring Plan [Member] \| Scott Safety business [Member] \| Other Restructuring [Member] \| Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash		0
2016 Restructuring Plan [Member] \| Scott Safety business [Member] \| Currency Translation \| Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash		0
Committed restructuring liabilities assumed from Tyco Merger [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			78
Restructuring Reserve, Settled without Cash		(22)
Committed restructuring liabilities assumed from Tyco Merger [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			56
Committed restructuring liabilities assumed from Tyco Merger [Member] \| Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			78
Restructuring Reserve, Settled without Cash		(22)
Committed restructuring liabilities assumed from Tyco Merger [Member] \| Fixed Asset Impairment
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			0
Restructuring Reserve, Settled without Cash		0
Committed restructuring liabilities assumed from Tyco Merger [Member] \| Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			0
Restructuring Reserve, Settled without Cash		0
Committed restructuring liabilities assumed from Tyco Merger [Member] \| Currency Translation
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			0
Restructuring Reserve, Settled without Cash		0
Building Solutions Asia Pacific \| Building Technologies & Solutions
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	16	16
Building Solutions Asia Pacific \| 2018 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	16
Building Solutions Asia Pacific \| 2017 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		16
Corporate \| 2018 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	50
Corporate \| 2017 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		166
Corporate \| 2016 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			161
Power Solutions \| 2018 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	8
Power Solutions \| 2017 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		20
Power Solutions \| 2016 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			66
Building Solutions EMEA/LA \| Building Technologies & Solutions
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	56	74	17
Building Solutions EMEA/LA \| 2018 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	56
Building Solutions EMEA/LA \| 2017 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		74
Building Solutions EMEA/LA \| 2016 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			17
Building Solutions North America \| Building Technologies & Solutions
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	20	59
Building Solutions North America \| 2018 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	20
Building Solutions North America \| 2017 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		59
Global Products \| Building Technologies & Solutions
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	113	32	44
Global Products \| 2018 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	$ 113
Global Products \| 2017 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		$ 32
Global Products \| 2016 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			$ 44