Fair Value Measurements (Details) - Fair value measurements recurring basis - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Total
Fair value of assets and liabilities measured on recurring basis
Short-term Investments	$ 154.4	$ 360.7
Forward contracts	34.8	11.0
Total	189.2	371.7
Level 1
Fair value of assets and liabilities measured on recurring basis
Short-term Investments	154.4	360.7
Total	154.4	360.7
Level 2
Fair value of assets and liabilities measured on recurring basis
Forward contracts	34.8	11.0
Total	$ 34.8	$ 11.0