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Acquisitions and Divestitures Divestitures (Details) $ in Millions		3 Months Ended							12 Months Ended
	Oct. 04, 2017 USD ($)	Sep. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)
Divestitures [Line Items]
Number of businesses divested		2
Business divestitures, net of cash divested									$ 220	$ 32	$ 1,646
Goodwill, written off related to divestiture									1,269	19
Gain on divestitures - net									$ 9	$ 26	$ 1,340
Building Solutions North America
Divestitures [Line Items]
Goodwill, written off related to divestiture						$ 3
Sales Price of Business Divestitures						16
Gain on divestitures - net						$ 14
Series of Individually Immaterial Business Acquisitions [Member]
Divestitures [Line Items]
Number of Businesses Acquired									3	2	3
ADT security business in South Africa [Member] \| Building Solutions EMEA/LA
Divestitures [Line Items]
Business divestitures, net of cash divested			$ 129
Goodwill, written off related to divestiture			$ 92
CBRE Group, Inc. [Member] [Member] \| Global Workplace Solutions
Divestitures [Line Items]
Proceeds from divestitures							$ 1,400
Goodwill, written off related to divestiture							220
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax							940
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax							643
Income tax expense from disposal											$ 297
Yanfeng Automotive Trim Systems [Member] \| Automotive Experience Interiors
Divestitures [Line Items]
Goodwill, written off related to divestiture							21
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax							145
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax							$ 38
Brookfield Johnson Controls [Member] \| Global Workplace Solutions
Divestitures [Line Items]
Goodwill, written off related to divestiture								$ 20
Number of Joint Ventures Divested								2
Proceeds from Divestiture of Interest in Joint Venture								$ 141
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax								200
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax								$ 127
Income tax expense from disposal											$ 73
Business Divestitures, Not Specific
Divestitures [Line Items]
Number of businesses divested				1	2						4
Proceeds from divestitures		$ 44		$ 4	$ 39						$ 119
Business divestitures, net of cash divested		40							$ 52	$ 29	86
Gain (loss) on divestiture		9			12						10
Cash Divested from Deconsolidation				$ 5	13
Business Divestitures, Not Specific \| Automotive Experience Seating
Divestitures [Line Items]
Goodwill, written off related to divestiture											4
Business Divestitures, Not Specific \| Building Solutions North America
Divestitures [Line Items]
Gain (loss) on divestiture											7
Goodwill, written off related to divestiture											2
Business Divestitures, Not Specific \| Building Efficiency Products North America [Member]
Divestitures [Line Items]
Gain (loss) on divestiture											38
Business Divestitures, Not Specific \| Global Products
Divestitures [Line Items]
Goodwill, written off related to divestiture		19			16						$ 14
Business Divestitures, Not Specific \| Building Solutions Asia Pacific
Divestitures [Line Items]
Goodwill, written off related to divestiture		$ 2
Tyco International Holding S.a.r.L. (TSarL) [Member]
Divestitures [Line Items]
Repayments of Debt									$ 300
Long-term Debt					$ 4,000					$ 4,000
Subsequent Event [Member] \| Scott Safety business [Member]
Divestitures [Line Items]
Proceeds from divestitures	$ 2,000
Subsequent Event [Member] \| Tyco International Holding S.a.r.L. (TSarL) [Member]
Divestitures [Line Items]
Repayments of Debt	$ 1,900