Income Taxes - Schedule of Components of Income Tax Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Components Of Deferred Income Tax Assets And Liabilities [Line Items]
(Loss) income from continuing operations before income taxes	$ (38.5)	$ 16.2	$ (86.4)	$ (20.2)
Deferred income taxes			(151.6)	(1.5)
Reported income tax expense	$ (1.2)	$ 24.0	$ (127.2)	$ 29.6