Goodwill and Other Intangible Assets - Changes in Carrying Amount of Goodwill (Details) $ in Millions	6 Months Ended
Mar. 31, 2018 USD ($)
Goodwill [Roll Forward]
Beginning Balance	$ 19,688
Business Acquisitions	8
Business Divestitures	(20)
Currency Translation and Other	130
Ending Balance	19,806
Power Solutions
Goodwill [Roll Forward]
Beginning Balance	1,097
Business Acquisitions	0
Business Divestitures	0
Currency Translation and Other	19
Ending Balance	1,116
Building Technologies & Solutions \| Building Solutions North America
Goodwill [Roll Forward]
Beginning Balance	9,637
Business Acquisitions	0
Business Divestitures	0
Currency Translation and Other	(22)
Ending Balance	9,615
Building Technologies & Solutions \| Building Solutions EMEA/LA
Goodwill [Roll Forward]
Beginning Balance	2,012
Business Acquisitions	0
Business Divestitures	0
Currency Translation and Other	77
Ending Balance	2,089
Building Technologies & Solutions \| Building Solutions Asia Pacific
Goodwill [Roll Forward]
Beginning Balance	1,255
Business Acquisitions	0
Business Divestitures	0
Currency Translation and Other	54
Ending Balance	1,309
Building Technologies & Solutions \| Global Products
Goodwill [Roll Forward]
Beginning Balance	5,687
Business Acquisitions	8
Business Divestitures	(20)
Currency Translation and Other	2
Ending Balance	$ 5,677

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

+ Details

Name:	us-gaap_Goodwill
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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.

+ References

+ Details

Name:	us-gaap_GoodwillAcquiredDuringPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

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.

+ References

+ Details

Name:	us-gaap_GoodwillForeignCurrencyTranslationGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

Name:	us-gaap_GoodwillRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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.

+ References

+ Details

Name:	us-gaap_GoodwillWrittenOffRelatedToSaleOfBusinessUnit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=jci_PowerSolutionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	jci_PrimaryBusinessInformationByPrimaryBusinessAxis=jci_BuildingTechnologiesSolutionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=jci_BuildingSolutionsNorthAmericaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=jci_BuildingSolutionsEMEALAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=jci_BuildingSolutionsAsiaPacificMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=jci_GlobalProductsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: