Debt, Interest Income, Expense and Other Finance Costs - Interest Income (Expense), and Other Financing Costs, net (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Debt, Interest Income, Expense and Other Finance Costs [Abstract]
Interest income	$ 0.6	$ 1.0
Interest expense and other financing costs	(16.9)	(13.7)
Interest income (expense) and other financing costs, net	$ (16.3)	$ (12.7)