Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Statement of Comprehensive Income [Abstract]
Net income	$ 3,513	$ 1,900	$ 2,033
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	(502)	39	(84)
Realized and unrealized gains (losses) on derivatives	15	(19)	25
Cumulative currency translation adjustment release	783	0	0
Pension and postretirement plans	(6)	(4)	(1)
Other comprehensive income (loss)	290	16	(60)
Total comprehensive income	3,803	1,916	1,973
Comprehensive income attributable to noncontrolling interests:
Net income	222	195	184
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	(37)	25	(15)
Realized and unrealized gains (losses) on derivatives	5	0	(1)
Other comprehensive income (loss)	(32)	25	(16)
Comprehensive income attributable to noncontrolling interests	190	220	168
Comprehensive income attributable to Johnson Controls	$ 3,613	$ 1,696	$ 1,805