Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 795	$ 5,887	$ 2,383
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	25	(342)	(483)
Realized and unrealized gains (losses) on derivatives	8	6	(29)
Realized and unrealized gains on marketable securities	0	0	4
Pension and postretirement plans	8	(6)	0
Other comprehensive income (loss)	41	(342)	(508)
Total comprehensive income	836	5,545	1,875
Comprehensive income attributable to noncontrolling interests	186	195	186
Comprehensive income attributable to Johnson Controls	$ 650	$ 5,350	$ 1,689