Significant Restructuring and Impairment Costs (Detail) $ in Millions	12 Months Ended				36 Months Ended
	Sep. 30, 2019 USD ($) Plant Employees	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2018 USD ($) Employees
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	$ 235	$ 255	$ 347
Restructuring Reserve				$ 445
Number of employees to be severed \| Employees					11,300
Restructuring and Related Cost, Number of Positions Eliminated, Inception to Date \| Employees	6,200
Restructuring And Related Cost Expected Number Of Plants To Be Closed \| Plant	12
Number Of Plants Closed \| Plant	11
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
Number of employees to be severed \| Employees					2,200
2017 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			367
Payments for Restructuring	$ (13)	(158)	(75)
Restructuring Reserve, Settled without Cash	(3)	(1)	(78)
Adjustment to restructuring reserves			25
Restructuring Reserve	61	80	239		$ 80
2017 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			347
2017 Restructuring Plan [Member] \| Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			276
Payments for Restructuring	(11)	(152)	(75)
Restructuring Reserve, Settled without Cash	0	0	0
Adjustment to restructuring reserves			25
Restructuring Reserve	60	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	0
Restructuring Reserve, Settled without Cash	0	0	(77)
Adjustment to restructuring reserves			0
Restructuring Reserve	0	0	0		0
2017 Restructuring Plan [Member] \| Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			14
Payments for Restructuring	(2)	(6)	0
Restructuring Reserve, Settled without Cash	0	0	(1)
Adjustment to restructuring reserves			0
Restructuring Reserve	5	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	0
Restructuring Reserve, Settled without Cash	(3)	(1)	0
Adjustment to restructuring reserves			0
Restructuring Reserve	(4)	(1)	0		(1)
2017 Restructuring Plan [Member] \| Power Solutions \| Discontinued Operations
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			20
2017 Restructuring Plan [Member] \| Power Solutions \| Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash	(3)
2017 Restructuring Plan [Member] \| Power Solutions \| Employee Severance \| Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash	(3)
2017 Restructuring Plan [Member] \| Power Solutions \| Fixed Asset Impairment \| Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash	0
2017 Restructuring Plan [Member] \| Power Solutions \| Other Restructuring [Member] \| Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash	0
2017 Restructuring Plan [Member] \| Power Solutions \| Currency Translation \| Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash	0
2018 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		263
Payments for Restructuring	(67)	(47)
Restructuring Reserve, Settled without Cash	(1)	(42)
Restructuring Reserve	102	174			174
2018 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		255
2018 Restructuring Plan [Member] \| Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		209
Payments for Restructuring	(61)	(45)
Restructuring Reserve, Settled without Cash	0	0
Restructuring Reserve	99	164			164
2018 Restructuring Plan [Member] \| Fixed Asset Impairment
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		42
Payments for Restructuring	0	0
Restructuring Reserve, Settled without Cash	0	(42)
Restructuring Reserve	0	0			0
2018 Restructuring Plan [Member] \| Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		12
Payments for Restructuring	(6)	(2)
Restructuring Reserve, Settled without Cash	0	0
Restructuring Reserve	4	10			10
2018 Restructuring Plan [Member] \| Currency Translation
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		0
Payments for Restructuring	0
Restructuring Reserve, Settled without Cash	(1)	0
Restructuring Reserve	(1)	0			0
2018 Restructuring Plan [Member] \| Power Solutions \| Discontinued Operations
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		8
2018 Restructuring Plan [Member] \| Power Solutions \| Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash	(4)
2018 Restructuring Plan [Member] \| Power Solutions \| Employee Severance \| Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash	(4)
2018 Restructuring Plan [Member] \| Power Solutions \| Fixed Asset Impairment \| Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash	0
2018 Restructuring Plan [Member] \| Power Solutions \| Other Restructuring [Member] \| Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash	0
2018 Restructuring Plan [Member] \| Power Solutions \| Currency Translation \| Transfer To Held for Sale [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash	0	0
2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs				620
Payments for Restructuring	(41)	(19)	(88)	(32)
Restructuring Reserve, Settled without Cash			1	(221)
Adjustment to restructuring reserves			(25)
Restructuring Reserve	32	73	92		73
2016 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs				222
2016 Restructuring Plan [Member] \| Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs				368
Payments for Restructuring	(37)	(17)	(86)	(32)
Restructuring Reserve, Settled without Cash			0	0
Adjustment to restructuring reserves			(25)
Restructuring Reserve	30	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	0
Restructuring Reserve, Settled without Cash			0	(190)
Adjustment to restructuring reserves			0
Restructuring Reserve	0	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	(4)	(2)	(2)	0
Restructuring Reserve, Settled without Cash			0	(32)
Adjustment to restructuring reserves			0
Restructuring Reserve	0	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	0
Restructuring Reserve, Settled without Cash			1	1
Adjustment to restructuring reserves			0
Restructuring Reserve	2	2	2	1	$ 2
2016 Restructuring Plan [Member] \| Adient \| Discontinued Operations
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs				398
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 \| 2017 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			16
Building Solutions Asia Pacific \| 2018 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		16
Corporate \| 2017 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			166
Corporate \| 2018 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		50
Corporate \| 2016 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs				161
Building Solutions EMEA/LA \| Building Technologies & Solutions
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		56	74
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 \| 2018 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		56
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 \| 2017 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			59
Building Solutions North America \| 2018 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		20
Global Products \| Building Technologies & Solutions
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	$ 235	113	32
Global Products \| 2017 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs			$ 32
Global Products \| 2018 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs		$ 113
Global Products \| 2016 Restructuring Plan [Member] \| Continuing Operations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs				$ 44