Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 1,344.3	$ 1,023.2	$ 695.8
Other comprehensive income (loss):
Pension and other postretirement benefit plan adjustments (net of tax (expense) benefit of ($181.0), ($3.4), and $150.0)	576.4	9.3	(475.6)
Currency translation adjustments	31.4	25.7	(55.3)
Net change in cash flow hedges (net of tax benefit of $3.1, $6.6, and $5.5)	(11.4)	(18.5)	(17.4)
Net change in available-for-sale investments	0.0	0.0	2.2
Other comprehensive income (loss)	596.4	16.5	(546.1)
Comprehensive income	1,940.7	1,039.7	149.7
Comprehensive loss attributable to noncontrolling interests	(14.5)	(0.5)	0.0
Comprehensive income attributable to Rockwell Automation, Inc.	$ 1,955.2	$ 1,040.2	$ 149.7