Earnings Per Share (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Earnings Per Share [Abstract]
Net income (loss) attributable to Johnson Controls	$ (277)	$ 133	$ 97	$ 251
Weighted Average Shares Outstanding
Basic weighted average shares outstanding (in shares)	679.0	686.8	679.9	686.9
Effect of dilutive securities:
Stock options, unvested restricted stock and unvested performance share awards (in shares)	0.0	2.9	1.6	3.1
Diluted weighted average shares outstanding (in shares)	679.0	689.7	681.5	690.0
Antidilutive Securities
Stock options and unvested restricted stock (in shares)	0.0	0.3	0.5	0.3
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock options and unvested restricted stock (in shares)	0.0	0.3	0.5	0.3
Share-Based Payment Arrangement
Antidilutive Securities
Stock options and unvested restricted stock (in shares)	1.6
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock options and unvested restricted stock (in shares)	1.6