Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Current allowance for credit losses
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 0.3	$ 0.3	$ 0.9
Charged to expenses	4.5	0.0	0.0
Charged to other accounts	(0.2)	0.0	(0.6)
Deductions	0.0	0.0	0.0
Balance at end of period	4.6	0.3	0.3
Deferred tax asset valuation allowance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	31.8	29.7	2.0
Charged to expenses	1.5	0.9	28.9
Charged to other accounts	0.0	1.2	0.0
Deductions	0.0	0.0	(1.2)
Balance at end of period	$ 33.3	$ 31.8	$ 29.7