Equity and Noncontrolling Interests Equity Attributable to Johnson Controls and Noncontrolling Interests (Additional Information) (Details)		3 Months Ended			12 Months Ended
	Sep. 02, 2016 USD ($) $ / shares shares	Sep. 30, 2018 USD ($) $ / shares	Sep. 30, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($)	Sep. 30, 2018 USD ($) $ / shares	Sep. 30, 2017 USD ($) $ / shares	Sep. 30, 2016 USD ($) $ / shares shares	Dec. 31, 2017 USD ($)
Equity, Class of Treasury Stock [Line Items]
Stockholders Equity, Change due to Merger							$ 15,808,000,000
Business Combination, Consideration Transferred	$ 19,671,000,000						$ 19,700,000,000
Stock repurchase program, authorized amount		$ 1,000,000,000			$ 1,000,000,000			$ 1,000,000,000
Business Combination, Number of Acquiree Shares Outstanding Prior to Acquisition | shares	427,181,743						427,200,000
Common Stock, Value, Issued	$ 9	$ 10,000,000	$ 9,000,000		$ 10,000,000	$ 9,000,000
Cash dividends common, per share | $ / shares		$ 0.26	$ 0.25		$ 1.04	$ 1.00	$ 1.16
Tyco share consolidation ratio	0.955						0.955
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares	407,958,565						408,000,000
Business Combination, Number of Acquiror Shares Outstanding Prior to Acquisition | shares							638,300,000
Cash consideration paid to JCI Inc. shareholders	$ 3,864,000,000						$ 3,864,000,000
Stockholder's equity, spin-off of Adient						$ (4,038,000,000)
Business Combination, Consideration Transferred per Share | $ / shares	$ 34.88						$ 34.88
Reduction in shares due to cash consideration paid by Tyco | shares	110,800,000						(110,800,000)
Business Combination, Adjusted Number of Acquiror Shares Outstanding Prior to Acquisition | shares							527,500,000
Common Stock, Shares, Outstanding | shares	935,500,000
Repurchases of common stock					$ 300,000,000	651,000,000	$ 501,000,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount		$ 1,000,000,000			1,000,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, NonControlling Interest	$ 37,000,000
Post Merger Stock Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount							1,000,000,000
PreMerger Share Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount		$ 3,650,000,000			3,650,000,000
Parent
Equity, Class of Treasury Stock [Line Items]
Stockholders Equity, Change due to Merger						(4,038,000,000)	(15,808,000,000)
Stockholder's equity, spin-off of Adient				$ 4,000,000,000
Repurchases of common stock					$ (300,000,000)	$ (651,000,000)	(501,000,000)
Tyco merger [Member]
Equity, Class of Treasury Stock [Line Items]
Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value							34,000,000
Hitachi Joint Venture [Member]
Equity, Class of Treasury Stock [Line Items]
Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value							$ 679,000,000