Goodwill and Other Intangible Assets - Other Intangibles (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Finite-Lived Intangible Assets [Line Items]
Goodwill acquired	$ 6.8	$ 0.8
Intangible assets acquired during year	3.0
Other intangible assets
Amortized intangible assets, carrying amount	453.8	457.8
Amortized intangible assets, accumulated amortization	282.3	263.5
Amortized intangible assets, net	171.5	194.3
Intangible asset amortization expense	28.2	30.2	$ 28.9
Allen-Bradley® trademark not subject to amortization	43.7	43.7
Total other intangible assets, carrying amount	497.5	501.5
Total other intangible assets, net	215.2	238.0
Goodwill and Other Intangible Assets (Textuals) [Abstract]
Estimated amortization expense in 2019	25.4
Estimated amortization expense in 2020	22.6
Estimated amortization expense in 2021	21.6
Estimated amortization expense in 2022	18.9
Estimated amortization expense in 2023	17.7
Computer software products
Other intangible assets
Amortized intangible assets, carrying amount	190.9	194.8
Amortized intangible assets, accumulated amortization	118.1	113.2
Amortized intangible assets, net	72.8	81.6
Intangible asset amortization expense	11.8	9.8	$ 11.5
Customer relationships
Other intangible assets
Amortized intangible assets, carrying amount	112.9	114.5
Amortized intangible assets, accumulated amortization	66.2	61.5
Amortized intangible assets, net	46.7	53.0
Technology
Other intangible assets
Amortized intangible assets, carrying amount	106.8	104.8
Amortized intangible assets, accumulated amortization	64.0	57.9
Amortized intangible assets, net	42.8	46.9
Trademarks
Other intangible assets
Amortized intangible assets, carrying amount	32.0	32.3
Amortized intangible assets, accumulated amortization	24.0	21.1
Amortized intangible assets, net	8.0	11.2
Other
Other intangible assets
Amortized intangible assets, carrying amount	11.2	11.4
Amortized intangible assets, accumulated amortization	10.0	9.8
Amortized intangible assets, net	$ 1.2	$ 1.6