Goodwill and Purchased Intangible Assets - Goodwill Allocated to Reportable Segments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Sep. 30, 2020
Goodwill [Line Items]
Gross	$ 2,128.7	$ 2,119.5
Accumulated Impairment	(1,110.0)	(1,110.0)
Net	1,018.7	1,009.5
Access Equipment
Goodwill [Line Items]
Gross	1,823.8	1,814.7
Accumulated Impairment	(932.1)	(932.1)
Net	891.7	882.6
Fire & Emergency
Goodwill [Line Items]
Gross	108.1	108.1
Accumulated Impairment	(2.0)	(2.0)
Net	106.1	106.1
Commercial
Goodwill [Line Items]
Gross	196.8	196.7
Accumulated Impairment	(175.9)	(175.9)
Net	$ 20.9	$ 20.8