Goodwill and Other Intangible Assets (Details 1) - USD ($) $ in Millions	Mar. 31, 2017	Sep. 30, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Total, carrying amount	$ 482.0	$ 485.0
Total, net	239.2	255.3
Other intangible assets
Amortized intangible assets, carrying amount	438.3	441.3
Amortized intangible assets, accumulated amortization	242.8	229.7
Amortized intangible assets, net	195.5	211.6
Goodwill and Other Intangible Assets (Textual) [Abstract]
Estimated amortization expense in 2017	29.8
Estimated amortization expense in 2018	25.0
Estimated amortization expense in 2019	21.8
Estimated amortization expense in 2020	19.1
Estimated amortization expense in 2021	18.4
Trademarks [Member]
Indefinite-lived Intangible Assets [Line Items]
Allen-Bradley® trademark not subject to amortization	43.7	43.7
Computer software products [Member]
Other intangible assets
Amortized intangible assets, carrying amount	182.4	182.4
Amortized intangible assets, accumulated amortization	108.2	103.4
Amortized intangible assets, net	74.2	79.0
Customer relationships [Member]
Other intangible assets
Amortized intangible assets, carrying amount	111.3	112.6
Amortized intangible assets, accumulated amortization	55.0	51.9
Amortized intangible assets, net	56.3	60.7
Technology [Member]
Other intangible assets
Amortized intangible assets, carrying amount	103.2	103.9
Amortized intangible assets, accumulated amortization	52.4	48.5
Amortized intangible assets, net	50.8	55.4
Trademarks [Member]
Other intangible assets
Amortized intangible assets, carrying amount	30.8	31.4
Amortized intangible assets, accumulated amortization	18.3	17.0
Amortized intangible assets, net	12.5	14.4
Other [Member]
Other intangible assets
Amortized intangible assets, carrying amount	10.6	11.0
Amortized intangible assets, accumulated amortization	8.9	8.9
Amortized intangible assets, net	$ 1.7	$ 2.1