Allowance for Doubtful Accounts - Allowance for Bad Debts (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance, beginning of year	$ 47.8	$ 39.8	$ 27.1
Provision for bad debts	12.5	12.4	10.4
Allowance charge-offs	(0.5)	(5.6)	(5.9)
Other	0.1	1.2	0.0
Balance, end of year	59.9	47.8	39.8	$ 27.1
Bad debt expense not included in allowance	4.0
Accounting Standards Update [Extensible Enumeration]				Accounting Standards Update 2016-13 [Member]
Cumulative transition adjustment
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance, beginning of year	0.0	0.0	8.2
Balance, end of year		0.0	0.0	$ 8.2
Adjusted balance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance, beginning of year	$ 47.8	39.8	35.3
Balance, end of year		$ 47.8	$ 39.8	$ 35.3