Accumulated Other Comprehensive Loss - Reclassifications out of Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other (expense) income	$ 2.9	$ 61.0
Sales	1,857.3	1,565.3
Cost of sales	(1,108.2)	(918.8)
Selling, general and administrative expenses	(447.5)	(374.6)
Interest expense	(29.6)	(22.6)
Income before income taxes	282.5	700.7
Income tax provision	(43.6)	(110.3)
Net income attributable to Rockwell Automation	241.5	593.3
Reclassification out of accumulated other comprehensive loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income attributable to Rockwell Automation	18.4	30.7
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	22.3	35.8
Income tax provision	(5.4)	(8.2)
Net income attributable to Rockwell Automation	16.9	27.6
Amortization of prior service credit | Reclassification out of accumulated other comprehensive loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other (expense) income	(0.2)	(1.0)
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	22.5	37.0
Settlements | Reclassification out of accumulated other comprehensive loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other (expense) income	0.0	(0.2)
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	1.8	4.3
Income tax provision	(0.3)	(1.2)
Net income attributable to Rockwell Automation	1.5	3.1
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	0.2	(0.5)
Cost of sales	0.6	4.7
Selling, general and administrative expenses	0.1	(0.4)
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