Summary of Significant Accounting Policies (Schedule of Allowance for Doubtful Receivables) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year	$ 3.5	$ 4.0	$ 4.1
Accounts Receivable, Credit Loss Expense (Reversal)	1.0	0.3	0.5
Balances written off, net of recoveries	0.0	(0.2)	(0.7)
Reclassification under ASC 606	0.0	(0.6)	0.0
Reclassifications	0.3	0.0	0.1
Balance at end of year	$ 4.8	$ 3.5	$ 4.0