Fair Value Measurements (Details) - Fair value measurements recurring basis - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Fair value of assets and liabilities measured on recurring basis
Short-term Investments	$ 22.1	$ 360.7
Forward contracts	21.2	11.0
Total	43.3	371.7
Level 1
Fair value of assets and liabilities measured on recurring basis
Short-term Investments	22.1	360.7
Total	22.1	360.7
Level 2
Fair value of assets and liabilities measured on recurring basis
Forward contracts	21.2	11.0
Total	$ 21.2	$ 11.0