Goodwill and Other Intangible Assets - Other Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019
Other intangible assets
Amortized intangible assets, carrying amount	$ 716.1	$ 453.5
Amortized intangible assets, accumulated amortization	318.0	303.1
Amortized intangible assets, net	398.1	150.4
Total, carrying amount	759.8	497.2
Total, net	441.8	194.1
Goodwill and Other Intangible Assets (Textual) [Abstract]
Estimated amortization expense in 2020	47.5
Estimated amortization expense in 2021	46.7
Estimated amortization expense in 2022	43.8
Estimated amortization expense in 2023	42.6
Estimated amortization expense in 2024	39.7
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	190.6
Amortized intangible assets, accumulated amortization	130.9	128.3
Amortized intangible assets, net	59.7	62.3
Customer relationships
Other intangible assets
Amortized intangible assets, carrying amount	305.2	110.5
Amortized intangible assets, accumulated amortization	75.6	69.2
Amortized intangible assets, net	229.6	41.3
Technology
Other intangible assets
Amortized intangible assets, carrying amount	154.2	110.4
Amortized intangible assets, accumulated amortization	73.3	69.5
Amortized intangible assets, net	80.9	40.9
Trademarks
Other intangible assets
Amortized intangible assets, carrying amount	55.3	31.4
Amortized intangible assets, accumulated amortization	28.3	26.4
Amortized intangible assets, net	27.0	5.0
Other
Other intangible assets
Amortized intangible assets, carrying amount	10.8	10.6
Amortized intangible assets, accumulated amortization	9.9	9.7
Amortized intangible assets, net	$ 0.9	$ 0.9