Earnings Per Share (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended
Dec. 31, 2024	Dec. 31, 2023
Income Available to Ordinary Shareholders
Discontinued operations	$ 56	$ 34
Continuing operations	363	340
Net income attributable to Johnson Controls	$ 419	$ 374
Weighted Average Shares Outstanding
Basic weighted average shares outstanding (in shares)	662.0	680.7
Effect of dilutive securities:
Stock options, unvested restricted stock and unvested performance share awards (in shares)	3.0	1.7
Diluted weighted average shares outstanding (in shares)	665.0	682.4
Antidilutive Securities
Stock options and unvested restricted stock (in shares)	0.0	0.6

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