Stockholders' Equity (Details 6) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jun. 30, 2008 item	Aug. 01, 2014	Feb. 28, 2013
Share Repurchase
Cost of shares repurchased	$ 483,077,000	$ 42,439,000	$ 188,000,000
Shareholder Rights Plan
Purchase price of each Right, before the amendment and restatement of the Rights (in dollars per one one-thousandth of a share)				64.75
Purchase price of each Right, after the amendment and restatement of the Rights (in dollars per one one-thousandth of a share)				400.00
Number of shares of Series A Junior Participating Preferred Stock each Right entitles a holder to purchase				0.001
Minimum ownership percentage in the outstanding shares of voting stock from the commencement of a tender offer that would result in the exercise of shares under one condition of the Agreement (as a percent)				15.00%
2014 Share Repurchase Program
Share Repurchase
Authorized aggregate repurchases of common stock	500,000,000				500,000,000
Period over which shares may be purchased under share repurchase program	1 year
Repurchased shares of common stock	887,114
Cost of shares repurchased	105,500,000
2013 Share Repurchase Program
Share Repurchase
Authorized aggregate repurchases of common stock						420,000,000
Repurchased shares of common stock	4,600,000
2012 Share Repurchase Program
Share Repurchase
Repurchased shares of common stock			4,000,000
Cost of shares repurchased			$ 188,000,000