Goodwill and Other Intangible Assets - Changes in Carrying Amount of Goodwill (Details) $ in Millions	6 Months Ended
Mar. 31, 2017 USD ($)
Goodwill [Roll Forward]
Beginning Balance	$ 21,024
Business Acquisitions	51
Business Divestitures	(1,261)
Currency Translation and Other	(170)
Ending Balance	19,644
Power Solutions
Goodwill [Roll Forward]
Beginning Balance	1,086
Business Acquisitions	0
Business Divestitures	0
Currency Translation and Other	(12)
Ending Balance	1,074
Building Technologies & Solutions [Member] \| Building Technologies & Solutions Tyco [Member]
Goodwill [Roll Forward]
Beginning Balance	16,308
Business Acquisitions	49
Business Divestitures	(1,261)
Currency Translation and Other	(124)
Ending Balance	14,972
Building Efficiency \| Building Efficiency Systems and Service North America
Goodwill [Roll Forward]
Beginning Balance	975
Business Acquisitions	0
Business Divestitures	0
Currency Translation and Other	0
Ending Balance	975
Building Efficiency \| Building Efficiency Products North America [Member]
Goodwill [Roll Forward]
Beginning Balance	1,697
Business Acquisitions	1
Business Divestitures	0
Currency Translation and Other	(2)
Ending Balance	1,696
Building Efficiency \| Building Efficiency Asia
Goodwill [Roll Forward]
Beginning Balance	657
Business Acquisitions	0
Business Divestitures	0
Currency Translation and Other	(23)
Ending Balance	634
Building Efficiency \| Building Efficiency Rest of World [Member]
Goodwill [Roll Forward]
Beginning Balance	301
Business Acquisitions	1
Business Divestitures	0
Currency Translation and Other	(9)
Ending Balance	$ 293

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=64834752&loc=SL49117168-202975

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