Convertible Senior Notes - Narrative (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	1 Months Ended	6 Months Ended
	Feb. 28, 2014 D	Jun. 30, 2014	Jun. 30, 2013
Debt Instrument [Line Items]
Debt issued	$ 690,000,000	$ 690,000,000
Conversion rate (in shares)	11.1651
Principal amount per conversion	1,000
Conversion price (in dollars per share)	$ 89.56
Threshold trading days exceeding price	20
Threshold consecutive trading days exceeding price	30 days
Threshold greater than percentage of stock price trigger	130.00%
Threshold trading days not exceeding price	5
Threshold consecutive trading days not exceeding price	5 days
Threshold less than percentage of stock price trigger	98.00%
Potential conversion shares of convertible debt (in shares)	7.7
Fair value of convertible senior notes		705,800,000
Closing price of common stock (in dollars per share)		$ 61.06
Repurchases of common stock	62,000,000	187,491,000	82,782,000
Payments for purchase of convertible note hedge and warrant transactions	23,300,000
Payments for note hedge transactions	101,300,000	101,292,000	0
Note hedge shares outstanding (in shares)	7.7
Warrants outstanding (in shares)	7.7
Warrant strike price (in dollars per share)	$ 104.49
Proceeds from sale of warrants	$ 78,000,000	$ 77,970,000	$ 0
Effective interest rate	3.20%