Debt (Details 2) - Convertible Notes Due 2016 $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) $ / shares shares
Sale of warrant
Share warrant, number of shares	5,200,000
Share warrant, exercise price (in dollars per share) | $ / shares	$ 67.56
Purchased call options
Purchase of call options
Convertible note hedge, approximate number of shares that can be purchased	5,200,000
Convertible note hedge, exercise price (in dollars per share) | $ / shares	$ 47.69
Call option, remaining shares	117,000
Call option, amount settlement | $	$ 133.2