Debt (Details 2) (Convertible Notes Due 2016, USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2014
Sale of warrant
Share warrant, number of shares	5.2	5.2
Share warrant, exercise price (in dollars per share)	$ 67.56	$ 67.56
Purchased call options
Purchase of call options
Convertible note hedge, approximate number of shares that can be purchased	5.2	5.2
Convertible note hedge, exercise price (in dollars per share)		$ 47.69
Call option, remaining shares	2.9	2.9
Call option, amount settlement	$ 111.3