Debt (Details 2) (Convertible Notes Due 2016, USD $) In Millions, except Per Share data, unless otherwise specified	6 Months Ended
	Jun. 30, 2013
Sale of warrant
Share warrant, number of shares	5.2
Share warrant, exercise price (in dollars per share)	$ 67.56
Purchased call options
Purchase of call options
Convertible note hedge, approximate number of shares that can be purchased	5.2
Convertible note hedge, exercise price (in dollars per share)	$ 47.69