Goodwill and Other Intangible Assets - Other Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Sep. 30, 2018
Other intangible assets
Amortized intangible assets, carrying amount	$ 450.3	$ 453.8
Amortized intangible assets, accumulated amortization	285.8	282.3
Amortized intangible assets, net	164.5	171.5
Total, carrying amount	494.0	497.5
Total, net	208.2	215.2
Goodwill and Other Intangible Assets (Textual) [Abstract]
Estimated amortization expense in 2019	24.5
Estimated amortization expense in 2020	21.6
Estimated amortization expense in 2021	20.9
Estimated amortization expense in 2022	18.9
Estimated amortization expense in 2023	17.7
Trademarks
Indefinite-lived Intangible Assets [Line Items]
Allen-Bradley® trademark not subject to amortization	43.7	43.7
Computer software products
Other intangible assets
Amortized intangible assets, carrying amount	190.9	190.9
Amortized intangible assets, accumulated amortization	120.8	118.1
Amortized intangible assets, net	70.1	72.8
Customer relationships
Other intangible assets
Amortized intangible assets, carrying amount	111.2	112.9
Amortized intangible assets, accumulated amortization	66.2	66.2
Amortized intangible assets, net	45.0	46.7
Technology
Other intangible assets
Amortized intangible assets, carrying amount	106.1	106.8
Amortized intangible assets, accumulated amortization	64.8	64.0
Amortized intangible assets, net	41.3	42.8
Trademarks
Other intangible assets
Amortized intangible assets, carrying amount	31.2	32.0
Amortized intangible assets, accumulated amortization	24.2	24.0
Amortized intangible assets, net	7.0	8.0
Other
Other intangible assets
Amortized intangible assets, carrying amount	10.9	11.2
Amortized intangible assets, accumulated amortization	9.8	10.0
Amortized intangible assets, net	$ 1.1	$ 1.2