Accumulated Other Comprehensive Loss - Reclassifications out of Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other (expense) income	$ (23.7)	$ (6.0)	$ (20.8)	$ 55.0
Sales	1,808.1	1,776.1	3,665.4	3,341.4
Cost of sales	(1,144.0)	(1,008.7)	(2,252.2)	(1,927.5)
Selling, general and administrative expenses	(428.5)	(421.3)	(876.0)	(795.9)
Interest expense	(30.1)	(23.3)	(59.7)	(45.9)
Income before income taxes	41.1	507.7	323.6	1,208.4
Income tax benefit (provision)	8.3	(97.4)	(35.3)	(207.7)
Net income attributable to Rockwell Automation, Inc.	53.9	415.0	295.4	1,008.3
Reclassification out of accumulated other comprehensive loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income attributable to Rockwell Automation, Inc.	34.8	33.7	53.2	64.4
Pension and other postretirement benefit plan adjustments | Reclassification out of accumulated other comprehensive loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	47.9	35.9	70.2	71.7
Income tax benefit (provision)	(12.2)	(8.5)	(17.6)	(16.7)
Net income attributable to Rockwell Automation, Inc.	35.7	27.4	52.6	55.0
Amortization of prior service cost (credit) | Reclassification out of accumulated other comprehensive loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other (expense) income	0.6	(1.0)	0.4	(2.0)
Amortization of net actuarial loss | Reclassification out of accumulated other comprehensive loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other (expense) income	22.4	37.1	44.9	74.1
Settlements | Reclassification out of accumulated other comprehensive loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other (expense) income	24.9	(0.2)	24.9	(0.4)
Net unrealized gains (losses) on cash flow hedges, net of tax | Reclassification out of accumulated other comprehensive loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	(1.2)	8.6	0.6	12.9
Income tax benefit (provision)	0.3	(2.3)	0.0	(3.5)
Net income attributable to Rockwell Automation, Inc.	(0.9)	6.3	0.6	9.4
Net unrealized gains (losses) on cash flow hedges, net of tax | Forward exchange contracts | Reclassification out of accumulated other comprehensive loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Sales	0.1	(0.7)	0.3	(1.2)
Cost of sales	(2.2)	9.3	(1.6)	14.0
Selling, general and administrative expenses	0.0	(0.5)	0.1	(0.9)
Net unrealized gains (losses) on cash flow hedges, net of tax | Treasury locks related to 2019 and 2021 debt issuances | Reclassification out of accumulated other comprehensive loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	$ 0.9	$ 0.5	$ 1.8	$ 1.0