Revenue Recognition - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2019
Disaggregation Of Revenue [Line Items]
Contract with Customer, Liability	$ 701.0		$ 701.0		$ 512.5
Customer advances	593.0		593.0		382.0
Contract with customer other current liability	56.7		56.7		78.2
Contract with Customer, Liability, Noncurrent	51.3		51.3		$ 52.3
Contract with Customer, Liability, Revenue Recognized	117.7	$ 237.4	290.6	$ 473.4
Fire and Emergency
Disaggregation Of Revenue [Line Items]
Interest Expense, Customer Deposits	$ 4.0	$ 3.7	$ 7.2	$ 7.3