Goodwill and Other Intangible Assets - Other Intangible Assets (Details) - USD ($) $ in Millions	Jun. 30, 2021	Sep. 30, 2020
Other intangible assets
Amortized intangible assets, carrying amount	$ 883.5	$ 795.9
Amortized intangible assets, accumulated amortization	414.4	360.3
Amortized intangible assets, net	469.1	435.6
Total, carrying amount	927.2	839.6
Total, net	512.8	479.3
Goodwill and Other Intangible Assets (Textual) [Abstract]
Estimated amortization expense, remainder of fiscal year	59.3
Estimated amortization expense in 2022	57.7
Estimated amortization expense in 2023	56.4
Estimated amortization expense in 2024	53.4
Estimated amortization expense in 2025	51.2
Trademarks
Other intangible assets
Allen-Bradley trademark not subject to amortization	43.7	43.7
Software products
Other intangible assets
Amortized intangible assets, carrying amount	197.2	192.7
Amortized intangible assets, accumulated amortization	147.4	139.0
Amortized intangible assets, net	49.8	53.7
Customer relationships
Other intangible assets
Amortized intangible assets, carrying amount	368.2	351.3
Amortized intangible assets, accumulated amortization	115.7	92.5
Amortized intangible assets, net	252.5	258.8
Technology
Other intangible assets
Amortized intangible assets, carrying amount	225.4	165.8
Amortized intangible assets, accumulated amortization	99.7	84.0
Amortized intangible assets, net	125.7	81.8
Trademarks
Other intangible assets
Amortized intangible assets, carrying amount	77.2	71.7
Amortized intangible assets, accumulated amortization	37.1	31.3
Amortized intangible assets, net	40.1	40.4
Other
Other intangible assets
Amortized intangible assets, carrying amount	15.5	14.4
Amortized intangible assets, accumulated amortization	14.5	13.5
Amortized intangible assets, net	$ 1.0	$ 0.9