Significant Restructuring Costs Change in Restructuring Reserve - 2017 Restructuring Plan (Details) - USD ($) $ in Millions	3 Months Ended					9 Months Ended		12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2018	Jun. 30, 2017	Sep. 30, 2017	Sep. 30, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs	$ 0	$ 158	$ 49	$ 99	$ 78	$ 158	$ 226
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						(146)		(75)
Restructuring Reserve, Settled without Cash						(1)		(78)
Adjustment to restructuring reserves								25
Restructuring Reserve	92					92		239
Employee Severance | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment costs								276
Payments for Restructuring						(142)		(75)
Restructuring Reserve, Settled without Cash						0		0
Adjustment to restructuring reserves								25
Restructuring Reserve	84					84		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						(4)		0
Restructuring Reserve, Settled without Cash						0		(1)
Adjustment to restructuring reserves								0
Restructuring Reserve	9					9		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