Allowance for Doubtful Accounts - Allowance for Bad Debts (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance, beginning of year	$ 27.1	$ 48.6	$ 58.2
Provision for (recovery of) bad debts	10.4	13.0	(9.8)
Allowance charge-offs	(5.9)	(35.6)	(1.3)
Other	0.0	1.1	1.5
Balance, end of year	39.8	27.1	48.6
Cumulative Effect, Period of Adoption, Adjustment
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance, beginning of year	8.2	0.0	0.0
Balance, end of year		8.2	0.0
Cumulative Effect, Period of Adoption, Adjusted Balance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance, beginning of year	$ 35.3	48.6	58.2
Balance, end of year		$ 35.3	$ 48.6