Schedule II-Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Allowance for doubtful accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 0.8	$ 0.8	$ 2.2
Change Charged to Expense	0.2	0.0	0.1
Other Changes	0.0	0.0	(1.5)
Balance at End of Period	1.0	0.8	0.8
Allowance for deferred tax assets
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	55.6	77.7	83.3
Change Charged to Expense	0.9	(20.8)	(4.9)
Other Changes	(55.6)	(1.3)	(0.7)
Balance at End of Period	$ 0.9	$ 55.6	$ 77.7