Commitments, Contingencies and Guarantees - Employee Retention Plan and Litigation (Details) € in Millions, $ in Millions	Dec. 31, 2017 EUR (€)	Dec. 31, 2017 USD ($)	Dec. 31, 2015 EUR (€)	Dec. 31, 2015 USD ($)
Litigation
Amount of fine	€ 3.3	$ 3.9	€ 5.0	$ 5.4