Revenue Recognition - Disaggregation of Revenue (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
Intersegment Eliminations
Disaggregation Of Revenue [Line Items]
Net sales													(25.4)	(18.1)	(24.6)
Transferred at Point in Time
Disaggregation Of Revenue [Line Items]
Net sales													4,078.1	5,801.1
Transferred at Point in Time | Intersegment Eliminations
Disaggregation Of Revenue [Line Items]
Net sales													(26.8)	(20.1)
Transferred over Time
Disaggregation Of Revenue [Line Items]
Net sales													2,778.7	2,580.9
Transferred over Time | Intersegment Eliminations
Disaggregation Of Revenue [Line Items]
Net sales													1.4	2.0
Access Equipment
Disaggregation Of Revenue [Line Items]
Net sales													2,505.7	4,079.7	3,776.8
Access Equipment | Operating Segments
Disaggregation Of Revenue [Line Items]
Net sales													2,515.1	4,079.7	3,776.8
Access Equipment | Intersegment Eliminations
Disaggregation Of Revenue [Line Items]
Net sales													9.4
Access Equipment | Transferred at Point in Time | Operating Segments
Disaggregation Of Revenue [Line Items]
Net sales													2,437.5	4,001.6
Access Equipment | Transferred over Time | Operating Segments
Disaggregation Of Revenue [Line Items]
Net sales													77.6	78.1
Defense
Disaggregation Of Revenue [Line Items]
Net sales													2,260.3	2,030.3	1,827.3
Defense | Operating Segments
Disaggregation Of Revenue [Line Items]
Net sales													2,262.2	2,032.1	1,828.9
Defense | Intersegment Eliminations
Disaggregation Of Revenue [Line Items]
Net sales													1.9	1.8	1.6
Defense | Transferred at Point in Time | Operating Segments
Disaggregation Of Revenue [Line Items]
Net sales													6.8	7.4
Defense | Transferred over Time | Operating Segments
Disaggregation Of Revenue [Line Items]
Net sales													2,255.4	2,024.7
Fire & Emergency
Disaggregation Of Revenue [Line Items]
Net sales													1,138.1	1,249.8	1,053.6
Fire & Emergency | Operating Segments
Disaggregation Of Revenue [Line Items]
Net sales													1,147.1	1,266.1	1,069.7
Fire & Emergency | Intersegment Eliminations
Disaggregation Of Revenue [Line Items]
Net sales													9.0	16.3	16.1
Fire & Emergency | Transferred at Point in Time | Operating Segments
Disaggregation Of Revenue [Line Items]
Net sales													1,103.9	1,220.5
Fire & Emergency | Transferred over Time | Operating Segments
Disaggregation Of Revenue [Line Items]
Net sales													43.2	45.6
Commercial
Disaggregation Of Revenue [Line Items]
Net sales													951.3	1,020.1	1,046.8
Commercial | Operating Segments
Disaggregation Of Revenue [Line Items]
Net sales													957.8	1,022.2	1,054.7
Commercial | Intersegment Eliminations
Disaggregation Of Revenue [Line Items]
Net sales													6.5	2.1	$ 7.9
Commercial | Transferred at Point in Time | Operating Segments
Disaggregation Of Revenue [Line Items]
Net sales													556.7	591.7
Commercial | Transferred over Time | Operating Segments
Disaggregation Of Revenue [Line Items]
Net sales													$ 401.1	$ 430.5

[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.