Summary of Significant Accounting Policies Accounting Policies (Details) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2017 USD ($) Segment $ / shares	Jun. 30, 2017 Segment	Sep. 30, 2017 USD ($) Segment $ / shares	Sep. 30, 2016 USD ($) $ / shares	Sep. 30, 2015 USD ($)	Oct. 31, 2016 shares	Sep. 02, 2016 $ / shares
Financial Statement Details [Line Items]
Maturity period to be considered cash equivalents			3 months
Restricted Cash and Cash Equivalents	$ 31		$ 31	$ 88
Restricted Cash and Investments, Current	22		22	79
Restricted Cash and Cash Equivalents, Noncurrent	9		9	9
Costs and earnings in excess of billings related to contracts	908		908	841
Billing in excess of costs and earnings on uncompleted contracts	451		451	431
Liability for Asbestos and Environmental Claims, Gross	$ 573		$ 573	548
Timing of the first deliverable to the last delivery			Approximately four to twelve months
Pooled subscriber assets and related deferred revenue, useful life			12 years
Non-pooled subscriber assets and related deferred revenue, useful life			15 years
Standard chargeback period from dealer for monitoring service cancellations			6 months
Non-standard chargeback period from dealer for monitoring service cancellations			12 months
Research and Development Expense			$ 360	158	$ 134
Foreign currency transaction gains (losses)			$ 94	$ (95)	$ (119)
Number of reportable segments | Segment	4	5	5
Adient shares received per 10 shares of Johnson Controls shares | shares						1
Ordinary shares, par value | $ / shares	$ 0.01		$ 0.01	$ 0.01			$ 1.00
Johnson Controls shares converted into one share of Adient | shares						10
Minimum
Financial Statement Details [Line Items]
Duration of extended warranty arrangements			1 year
Estimated useful life of dealer intangible assets			12 years
Maximum
Financial Statement Details [Line Items]
Duration of extended warranty arrangements			5 years
Estimated useful life of dealer intangible assets			15 years
Building And Improvements | Minimum
Financial Statement Details [Line Items]
Estimated useful lives			3 years
Building And Improvements | Maximum
Financial Statement Details [Line Items]
Estimated useful lives			40 years
Machinery and Equipment | Minimum
Financial Statement Details [Line Items]
Estimated useful lives			3 years
Machinery and Equipment | Maximum
Financial Statement Details [Line Items]
Estimated useful lives			15 years
Johnson Controls International plc [Member]
Financial Statement Details [Line Items]
Proceeds from Issuance of Unsecured Debt			$ 1,500
Adient
Financial Statement Details [Line Items]
Proceeds from Issuance of Unsecured Debt			$ 500
Tyco Merger [Member]
Financial Statement Details [Line Items]
Ordinary shares, par value | $ / shares							$ 1.00