Interest Income, Expense and Other Financing Costs (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Interest Income, Expense and Other Financing Costs    
Interest income $ 1.2 $ 1.6
Interest expense and other financing costs (8.5) (6.0)
Interest expense and other financing costs, net $ (7.3) $ (4.4)