Significant Restructuring Costs Change in Restructuring Reserve - 2016 Restructuring Plan (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	$ 0	$ 154
2016 Restructuring Plan [Domain]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					$ 222
2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					620
Restructuring Reserve	65		$ 73	$ 92	445
Payments for Restructuring	(8)		(19)	(88)	(32)
Restructuring Reserve, Settled without Cash				1	(221)
Adjustment to restructuring reserves				(25)
Employee Severance | 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					368
Restructuring Reserve	59		67	84	414
Payments for Restructuring	(8)		(17)	(86)	(32)
Restructuring Reserve, Settled without Cash				0	0
Adjustment to restructuring reserves				(25)
Fixed Asset Impairment | 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					190
Restructuring Reserve	0		0	0	0
Payments for Restructuring	0		0	0	0
Restructuring Reserve, Settled without Cash				0	(190)
Adjustment to restructuring reserves				0
Other Restructuring | 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					62
Restructuring Reserve	4		4	6	30
Payments for Restructuring	0		(2)	(2)	0
Restructuring Reserve, Settled without Cash				0	(32)
Adjustment to restructuring reserves				0
Currency Translation | 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					0
Restructuring Reserve	2		2	2	1
Payments for Restructuring	0		$ 0	0	0
Restructuring Reserve, Settled without Cash				1	1
Adjustment to restructuring reserves				0
Tyco merger [Member] | 2016 Restructuring Plan [Domain]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					78
Restructuring Reserve	$ 56
Restructuring Reserve, Settled without Cash				(22)
Tyco merger [Member] | Employee Severance | 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					78
Restructuring Reserve, Settled without Cash				(22)
Tyco merger [Member] | Fixed Asset Impairment | 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					0
Restructuring Reserve, Settled without Cash				0
Tyco merger [Member] | Other Restructuring | 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					0
Restructuring Reserve, Settled without Cash				0
Tyco merger [Member] | Currency Translation | 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					0
Restructuring Reserve, Settled without Cash				0
Building Solutions EMEA/LA | 2016 Restructuring Plan [Domain]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					17
Corporate Segment | 2016 Restructuring Plan [Domain]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					161
Global Products | 2016 Restructuring Plan [Domain]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					44
Adient spin-off [Member] | Transfer To Held for Sale [Member] | 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash				(216)
Adient spin-off [Member] | Transfer To Held for Sale [Member] | Employee Severance | 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash				(194)
Adient spin-off [Member] | Transfer To Held for Sale [Member] | Fixed Asset Impairment | 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash				0
Adient spin-off [Member] | Transfer To Held for Sale [Member] | Other Restructuring | 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash				(22)
Adient spin-off [Member] | Transfer To Held for Sale [Member] | Currency Translation | 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash				0
Scott Safety business [Member] | Transfer To Held for Sale [Member] | 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash				(3)
Scott Safety business [Member] | Transfer To Held for Sale [Member] | Employee Severance | 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash				(3)
Scott Safety business [Member] | Transfer To Held for Sale [Member] | Fixed Asset Impairment | 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash				0
Scott Safety business [Member] | Transfer To Held for Sale [Member] | Other Restructuring | 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash				0
Scott Safety business [Member] | Transfer To Held for Sale [Member] | Currency Translation | 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash				$ 0
Power Solutions and Adient [Member] | Discontinued Operations | 2016 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					$ 398