Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 1,023.2	$ 695.8	$ 535.5
Other comprehensive (loss) income:
Pension and other postretirement benefit plan adjustments (net of tax (expense) benefit of ($3.4), $150.0, and ($87.2))	9.3	(475.6)	268.9
Currency translation adjustments	25.7	(55.3)	(48.3)
Net change in cash flow hedges (net of tax benefit (expense) of $6.6, $5.5, and ($6.6))	(18.5)	(17.4)	18.8
Net change in available-for-sale investments	0.0	2.2	(2.1)
Other comprehensive (loss) income	16.5	(546.1)	237.3
Comprehensive income	1,039.7	149.7	772.8
Comprehensive loss attributable to noncontrolling interests	(0.5)	0.0	0.0
Comprehensive income attributable to Rockwell Automation, Inc.	$ 1,040.2	$ 149.7	$ 772.8