Income Taxes - Summary of Tax Cuts and Jobs Act of 2017 Effects (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Reduction in net deferred tax liabilities in the U.S. from the reduction of the U.S. tax rate	$ 0.0	$ 180.3	$ 180.3
Establishment of valuation allowances related to deferred tax assets impacted by TCJA	5.0	(12.6)	(7.6)
Toll-tax on un-repatriated earnings	0.3	(1.7)	(1.4)
Total discrete deferred income tax adjustments	$ 5.3	$ 166.0	$ 171.3
Basic earnings per share (USD per share)	$ 0.03	$ 0.96	$ 0.99
Diluted earnings per share (USD per share)	$ 0.03	$ 0.94	$ 0.97

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Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Change In Tax Rate, Deferred Tax Asset, Provisional Income Tax Expense (Benefit)

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