Debt, Interest Income, Expense and Other Finance Costs - Additional Information about Interest Income (Expense), and Other Financing Costs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Debt, Interest Income, Expense and Other Finance Costs [Abstract]
Interest income	$ 1.2	$ 0.8	$ 3.9	$ 3.6
Interest expense and other financing costs	(17.0)	(11.0)	(46.2)	(29.5)
Interest income (expense) and other financing costs, net	$ (15.8)	$ (10.3)	$ (42.2)	$ (26.0)