Goodwill and Other Intangible Assets Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Jun. 30, 2016	Sep. 30, 2018	Sep. 30, 2017
Goodwill [Roll Forward]
Goodwill, Beginning Balance		$ 19,688	$ 21,024
Business Acquisitions		15	(256)
Business Divestitures		(35)	(1,269)
Currency Translation and Other		(195)	189
Goodwill, Ending Balance		19,473	19,688
Power Solutions
Goodwill [Roll Forward]
Goodwill, Beginning Balance		1,097	1,086
Business Acquisitions		0	0
Business Divestitures		0	0
Currency Translation and Other		(5)	11
Goodwill, Ending Balance		1,092	1,097
Building Solutions North America
Goodwill [Roll Forward]
Business Divestitures	$ (3)
Building Solutions North America \| Building Technologies & Solutions
Goodwill [Roll Forward]
Goodwill, Beginning Balance		9,637	9,734
Business Acquisitions		0	(147)
Business Divestitures		0	0
Currency Translation and Other		(34)	50
Goodwill, Ending Balance		9,603	9,637
Building Solutions EMEA/LA \| Building Technologies & Solutions
Goodwill [Roll Forward]
Goodwill, Beginning Balance		2,012	1,981
Business Acquisitions		1	(37)
Business Divestitures		0	0
Currency Translation and Other		(63)	68
Goodwill, Ending Balance		1,950	2,012
Building Solutions Asia Pacific \| Building Technologies & Solutions
Goodwill [Roll Forward]
Goodwill, Beginning Balance		1,255	1,260
Business Acquisitions		0	(14)
Business Divestitures		0	(2)
Currency Translation and Other		(20)	11
Goodwill, Ending Balance		1,235	1,255
Global Products \| Building Technologies & Solutions
Goodwill [Roll Forward]
Goodwill, Beginning Balance		5,687	6,963
Business Acquisitions		14	(58)
Business Divestitures		(35)	(1,267)
Currency Translation and Other		(73)	49
Goodwill, Ending Balance		$ 5,593	$ 5,687

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

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Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of divestiture of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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