Goodwill and Other Intangible Assets - Other Intangible Assets (Details) - USD ($)	6 Months Ended
	Mar. 31, 2020	Sep. 30, 2019
Other intangible assets
Amortized intangible assets, carrying amount	$ 715,700,000	$ 453,500,000
Amortized intangible assets, accumulated amortization	326,400,000	303,100,000
Amortized intangible assets, net	389,300,000	150,400,000
Total, carrying amount	759,400,000	497,200,000
Total, net	433,000,000.0	194,100,000
Goodwill and Other Intangible Assets (Textual) [Abstract]
Estimated amortization expense in 2020	47,900,000
Estimated amortization expense in 2021	47,200,000
Estimated amortization expense in 2022	44,300,000
Estimated amortization expense in 2023	43,100,000
Estimated amortization expense in 2024	40,100,000
Asset impairment charges	0
Trademarks
Indefinite-lived Intangible Assets [Line Items]
Allen-Bradley® trademark not subject to amortization	43,700,000	43,700,000
Computer software products
Other intangible assets
Amortized intangible assets, carrying amount	190,600,000	190,600,000
Amortized intangible assets, accumulated amortization	133,400,000	128,300,000
Amortized intangible assets, net	57,200,000	62,300,000
Customer relationships
Other intangible assets
Amortized intangible assets, carrying amount	305,400,000	110,500,000
Amortized intangible assets, accumulated amortization	77,600,000	69,200,000
Amortized intangible assets, net	227,800,000	41,300,000
Technology
Other intangible assets
Amortized intangible assets, carrying amount	152,000,000.0	110,400,000
Amortized intangible assets, accumulated amortization	75,100,000	69,500,000
Amortized intangible assets, net	76,900,000	40,900,000
Trademarks
Other intangible assets
Amortized intangible assets, carrying amount	53,900,000	31,400,000
Amortized intangible assets, accumulated amortization	27,500,000	26,400,000
Amortized intangible assets, net	26,400,000	5,000,000.0
Other
Other intangible assets
Amortized intangible assets, carrying amount	13,800,000	10,600,000
Amortized intangible assets, accumulated amortization	12,800,000	9,700,000
Amortized intangible assets, net	$ 1,000,000.0	$ 900,000