Significant Restructuring Costs Change in Restructuring Reserve - 2017 Restructuring Plan (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	$ 111	$ 0
2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					$ 367
Payments for Restructuring	(10)		$ (13)	$ (158)	(75)
Restructuring Reserve, Settled without Cash			(3)	(1)	(78)
Adjustment to restructuring reserves					25
Restructuring Reserve	46		61	80	239
Employee Severance | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					276
Payments for Restructuring	(10)		(11)	(152)	(75)
Restructuring Reserve, Settled without Cash			0	0	0
Adjustment to restructuring reserves					25
Restructuring Reserve	50		60	74	226
Fixed Asset Impairment | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					77
Payments for Restructuring	0		0	0	0
Restructuring Reserve, Settled without Cash			0	0	(77)
Adjustment to restructuring reserves					0
Restructuring Reserve	0		0	0	0
Other Restructuring | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					14
Payments for Restructuring	0		(2)	(6)	0
Restructuring Reserve, Settled without Cash			0	0	(1)
Adjustment to restructuring reserves					0
Restructuring Reserve	0		5	7	13
Currency Translation | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					0
Payments for Restructuring	0		0	0	0
Restructuring Reserve, Settled without Cash			(3)	(1)	0
Adjustment to restructuring reserves					0
Restructuring Reserve	(4)		(4)	$ (1)	0
Corporate Segment | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					166
Building Technologies & Solutions EMEA LA [Member] | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					74
Building Solutions North America | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					59
Building Solutions Asia Pacific | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					16
Global Products | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					32
Continuing Operations | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					347
Power Solutions | Transfer To Held for Sale [Member] | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash			(3)
Power Solutions | Transfer To Held for Sale [Member] | Employee Severance | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash			(3)
Power Solutions | Transfer To Held for Sale [Member] | Fixed Asset Impairment | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash			0
Power Solutions | Transfer To Held for Sale [Member] | Other Restructuring | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash			0
Power Solutions | Transfer To Held for Sale [Member] | Currency Translation | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Settled without Cash			$ 0
Power Solutions | Discontinued Operations | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs					$ 20
Accounting Standards Update 2016-02 [Member] | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Translation and Other Adjustment	(5)
Accounting Standards Update 2016-02 [Member] | Employee Severance | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Translation and Other Adjustment	0
Accounting Standards Update 2016-02 [Member] | Fixed Asset Impairment | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Translation and Other Adjustment	0
Accounting Standards Update 2016-02 [Member] | Other Restructuring | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Translation and Other Adjustment	(5)
Accounting Standards Update 2016-02 [Member] | Currency Translation | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Translation and Other Adjustment	$ 0