Contingencies, Significant Estimates and Concentrations - Schedule of Significant Portion of Revenues from the Department of Defense (Details) - USD ($) $ in Millions	3 Months Ended												12 Months Ended
	Sep. 30, 2020	[1]	Jun. 30, 2020	[2]	Mar. 31, 2020	[3]	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	[4]	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Disaggregation Of Revenue [Line Items]
Net sales	$ 1,784.2		$ 1,580.8		$ 1,796.7		$ 1,695.1	$ 2,195.7	$ 2,392.7	$ 1,990.2	$ 1,803.4		$ 6,856.8	$ 8,382.0	$ 7,705.5
DoD
Disaggregation Of Revenue [Line Items]
Net sales													2,300.4	2,006.9	1,648.4
Foreign Military
Disaggregation Of Revenue [Line Items]
Net sales													71.2	27.7	28.0
Total DoD Sales
Disaggregation Of Revenue [Line Items]
Net sales													$ 2,371.6	$ 2,034.6	$ 1,676.4

[1] ^{The fourth quarter of fiscal 2020 was impacted by restructuring-related charges of $13.0 million ($9.5 million, net of tax) in the Access Equipment, Fire & Emergency and Commercial segments and Corporate, a gain of $4.2 million ($3.2 million, net of tax) for an arbitration settlement in the Defense segment, business interruption insurance proceeds of $18.5 million ($14.2 million, net of tax) in the Commercial segment and a gain on the sale of a business of $3.1 million ($2.8 million net of tax) in the Commercial segment.}

[2] ^{The third quarter of fiscal 2020 was impacted by restructuring charges of $10.2 million ($8.4 million, net of tax) in the Access Equipment, Fire & Emergency and Commercial segments.}

[3] ^{The second quarter of fiscal 2020 was impacted by debt extinguishment costs of $8.5 million ($6.5 million, net of tax) and a tax charge of $11.4 million related to the establishment of a valuation allowance on net operating losses for an entity in Europe.}

[4] The first quarter of fiscal 2019 was impacted by tax expense related to tax reform in the U.S. of $7.0 million.