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, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017	Sep. 30, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	$ 0	$ 158	$ 99	$ 78	$ 158	$ 177
2016 Restructuring Plan [Domain]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs								$ 288
2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							$ 367
Payments for Restructuring					(112)		(75)
Restructuring Reserve, Settled without Cash					1		(78)
Adjustment to restructuring reserves							25
Restructuring Reserve	128				128		239
Employee Severance | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							276
Payments for Restructuring					(109)		(75)
Restructuring Reserve, Settled without Cash					0		0
Adjustment to restructuring reserves							25
Restructuring Reserve	117				117		226
Fixed Asset Impairment | 2017 Restructuring Plan
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
Other Restructuring | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							14
Payments for Restructuring					(3)		0
Restructuring Reserve, Settled without Cash					0		(1)
Adjustment to restructuring reserves							0
Restructuring Reserve	10				10		13
Currency Translation | 2017 Restructuring Plan
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				$ 1		0
Corporate Segment | 2016 Restructuring Plan [Domain]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs								161
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
Power Solutions | 2016 Restructuring Plan [Domain]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs								66
Power Solutions | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							20
Building Solutions Asia Pacific | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							16
Global Products | 2016 Restructuring Plan [Domain]
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs								$ 44
Global Products | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs							$ 32