Debt, Interest Income, Expense, and Other Finance Costs - Interest Income (Expense), and Other Financing Costs, net (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Debt Disclosure [Abstract]
Interest income	$ 1.7	$ 0.7	$ 5.4	$ 2.3
Interest expense and other financing costs	(12.1)	(9.4)	(34.6)	(36.3)
Interest expense and other financing costs, net	$ (10.4)	$ (8.7)	$ (29.2)	$ (34.1)