Significant Restructuring Costs Change in Restructuring Reserve - 2017 Restructuring Plan (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	$ 0	$ 0	$ 154	$ 0	$ 154
2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							$ 367
Payments for Restructuring				(4)		$ (158)	(75)
Restructuring Reserve, Settled without Cash				(2)		(1)	(78)
Adjustment to restructuring reserves							25
Restructuring Reserve	71			71		80	239
Employee Severance | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							276
Payments for Restructuring				(3)		(152)	(75)
Restructuring Reserve, Settled without Cash				0		0	0
Adjustment to restructuring reserves							25
Restructuring Reserve	68			68		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
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				(1)		(6)	0
Restructuring Reserve, Settled without Cash				0		0	(1)
Adjustment to restructuring reserves							0
Restructuring Reserve	6			6		7	13
Currency Translation | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							0
Payments for Restructuring				0		0	0
Restructuring Reserve, Settled without Cash				(2)		(1)	0
Adjustment to restructuring reserves							0
Restructuring Reserve	$ (3)			(3)		$ (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