Goodwill and Other Intangible Assets - Other Intangible Assets (Details) - USD ($) $ in Millions	Jun. 30, 2019	Sep. 30, 2018
Other intangible assets
Amortized intangible assets, carrying amount	$ 456.3	$ 453.8
Amortized intangible assets, accumulated amortization	299.1	282.3
Amortized intangible assets, net	157.2	171.5
Total, carrying amount	500.0	497.5
Total, net	200.9	215.2
Goodwill and Other Intangible Assets (Textual) [Abstract]
Estimated amortization expense in 2019	25.2
Estimated amortization expense in 2020	22.6
Estimated amortization expense in 2021	21.9
Estimated amortization expense in 2022	19.9
Estimated amortization expense in 2023	18.7
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	190.6	190.9
Amortized intangible assets, accumulated amortization	125.7	118.1
Amortized intangible assets, net	64.9	72.8
Customer relationships
Other intangible assets
Amortized intangible assets, carrying amount	111.9	112.9
Amortized intangible assets, accumulated amortization	69.2	66.2
Amortized intangible assets, net	42.7	46.7
Technology
Other intangible assets
Amortized intangible assets, carrying amount	111.1	106.8
Amortized intangible assets, accumulated amortization	68.3	64.0
Amortized intangible assets, net	42.8	42.8
Trademarks
Other intangible assets
Amortized intangible assets, carrying amount	31.8	32.0
Amortized intangible assets, accumulated amortization	26.0	24.0
Amortized intangible assets, net	5.8	8.0
Other
Other intangible assets
Amortized intangible assets, carrying amount	10.9	11.2
Amortized intangible assets, accumulated amortization	9.9	10.0
Amortized intangible assets, net	$ 1.0	$ 1.2