Interest Income, Expense and Other Financing Costs (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Interest Income, Expense and Other Financing Costs
Interest income	[1]	$ 1.5	$ 1.3	$ 2.8	$ 2.6
Interest expense and other financing costs	[1]	(9.6)	(7.7)	(18.5)	(16.3)
Interest expense and other financing costs, net	[1]	$ (8.1)	$ (6.4)	$ (15.7)	$ (13.7)

[1] Amounts may not add due to rounding