Goodwill and Other Intangible Assets - Other Intangibles (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Other intangible assets
Amortized intangible assets, carrying amount		$ 453,500,000	$ 453,800,000
Amortized intangible assets, accumulated amortization		303,100,000	282,300,000
Amortized intangible assets, net		150,400,000	171,500,000
Total other intangible assets, carrying amount		497,200,000	497,500,000
Total other intangible assets, net		194,100,000	215,200,000
Intangible asset amortization expense		26,000,000.0	28,200,000	$ 30,200,000
Goodwill and Other Intangible Assets (Textuals) [Abstract]
Estimated amortization expense in 2019		23,400,000
Estimated amortization expense in 2020		22,600,000
Estimated amortization expense in 2021		19,900,000
Estimated amortization expense in 2022		18,700,000
Estimated amortization expense in 2023		16,800,000
Goodwill and intangible asset impairment	$ 0
Computer software products
Other intangible assets
Amortized intangible assets, carrying amount		190,600,000	190,900,000
Amortized intangible assets, accumulated amortization		128,300,000	118,100,000
Amortized intangible assets, net		62,300,000	72,800,000
Intangible asset amortization expense		10,400,000	11,800,000	$ 9,800,000
Customer relationships
Other intangible assets
Amortized intangible assets, carrying amount		110,500,000	112,900,000
Amortized intangible assets, accumulated amortization		69,200,000	66,200,000
Amortized intangible assets, net		41,300,000	46,700,000
Technology
Other intangible assets
Amortized intangible assets, carrying amount		110,400,000	106,800,000
Amortized intangible assets, accumulated amortization		69,500,000	64,000,000.0
Amortized intangible assets, net		40,900,000	42,800,000
Trademarks
Other intangible assets
Amortized intangible assets, carrying amount		31,400,000	32,000,000.0
Amortized intangible assets, accumulated amortization		26,400,000	24,000,000.0
Amortized intangible assets, net		5,000,000.0	8,000,000.0
Other
Other intangible assets
Amortized intangible assets, carrying amount		10,600,000	11,200,000
Amortized intangible assets, accumulated amortization		9,700,000	10,000,000.0
Amortized intangible assets, net		900,000	1,200,000
Trademarks
Other intangible assets
Allen-Bradley® trademark not subject to amortization		$ (43,700,000)	$ (43,700,000)