Financial Instruments - Derivative Instruments Used to Hedge against Balance Sheet Foreign Currency Exposures (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign exchange gains (losses) related to balance sheet re-measurement	$ (5.6)	$ (7.9)	$ (6.9)
Foreign Exchange Forward | Other income | Derivatives Not Designated as Hedging Instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recognized gains (losses) in interest and other income, net	$ 6.4	$ 7.0	$ 5.7