Fair Values of Financial Instruments (Details 2) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions    
Total Carrying Value $ 1,136.4 $ 1,137.6
Total borrowings 1,139.0 1,140.4
Fair Value, Inputs, Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions    
Estimated Fair Value $ 1,134.5 $ 1,102.0