Goodwill and Other Intangible Assets - Changes in Carrying Amount of Goodwill (Details) $ in Millions	9 Months Ended
Jun. 30, 2018 USD ($)
Goodwill [Roll Forward]
Beginning Balance	$ 19,688
Business Acquisitions	12
Business Divestitures	(20)
Currency Translation and Other	(168)
Ending Balance	19,512
Power Solutions
Goodwill [Roll Forward]
Beginning Balance	1,097
Business Acquisitions	0
Business Divestitures	0
Currency Translation and Other	(2)
Ending Balance	1,095
Building Technologies & Solutions \| Building Solutions North America
Goodwill [Roll Forward]
Beginning Balance	9,637
Business Acquisitions	0
Business Divestitures	0
Currency Translation and Other	(45)
Ending Balance	9,592
Building Technologies & Solutions \| Building Solutions EMEA/LA
Goodwill [Roll Forward]
Beginning Balance	2,012
Business Acquisitions	0
Business Divestitures	0
Currency Translation and Other	(53)
Ending Balance	1,959
Building Technologies & Solutions \| Building Solutions Asia Pacific
Goodwill [Roll Forward]
Beginning Balance	1,255
Business Acquisitions	0
Business Divestitures	0
Currency Translation and Other	2
Ending Balance	1,257
Building Technologies & Solutions \| Global Products
Goodwill [Roll Forward]
Beginning Balance	5,687
Business Acquisitions	12
Business Divestitures	(20)
Currency Translation and Other	(70)
Ending Balance	$ 5,609

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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