Basis of Presentation and Accounting Policies - Reconciliation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Reconciled Basic and Diluted EPS
Net income attributable to Rockwell Automation, Inc.	$ 262.7	$ 317.8	$ 132.2	$ 310.7	$ 8.1	$ 261.4	$ 346.0	$ 80.3	$ 1,023.4	$ 695.8	$ 535.5
Less: Allocation to participating securities									(1.0)	(0.7)	(0.5)
Net income available to common shareowners									$ 1,022.4	$ 695.1	$ 535.0
Basic weighted average outstanding shares (in shares)									115.8	118.3	125.4
Effect of dilutive securities
Diluted weighted average outstanding shares (in shares)									116.6	119.3	126.9
Earnings per share:
Basic (in dollars per share)	$ 2.26	$ 2.74	$ 1.14	$ 2.68	$ 0.07	$ 2.22	$ 2.91	$ 0.67	$ 8.83	$ 5.88	$ 4.27
Diluted (in dollars per share)	$ 2.25	$ 2.73	$ 1.13	$ 2.66	$ 0.07	$ 2.20	$ 2.88	$ 0.66	$ 8.77	$ 5.83	$ 4.21
Stock options
Effect of dilutive securities
Stock options (in shares)									0.7	0.9	1.3
Performance shares
Effect of dilutive securities
Stock options (in shares)									0.1	0.1	0.2