Equity and Noncontrolling Interests Equity Attributable to Johnson Controls and Noncontrolling Interests (Additional Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Mar. 31, 2019
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount				$ 8,500
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 2,400
Stock Repurchased and Retired During Period, Value	2,204
Repurchases of ordinary shares		$ 5,983	$ 300
Stock Repurchased and Retired During Period Value Tender Offer		4,035
Stock Repurchased and Retired During Period Value Open Market		1,948
Parent
Equity, Class of Treasury Stock [Line Items]
Repurchases of ordinary shares	2,204	5,983	300
Stockholders' Equity, Total
Equity, Class of Treasury Stock [Line Items]
Repurchases of ordinary shares	$ 2,204	$ 5,983	$ 300