Earnings Per Share (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Income Available to Ordinary Shareholders
Income from continuing operations	$ 1,721	$ 1,407	$ 1,562
Income from discontinued operations	1,570	298	287
Net income attributable to Johnson Controls	$ 3,291	$ 1,705	$ 1,849
Weighted Average Shares Outstanding
Basic weighted average shares outstanding (in shares)	651.8	673.8	684.3
Effect of dilutive securities:
Stock options, unvested restricted stock and unvested performance share awards (in shares)	2.3	2.2	3.1
Diluted weighted average shares outstanding (in shares)	654.1	676.0	687.4
Antidilutive Securities
Stock options and unvested restricted stock (in shares)	0.1	0.3	0.2