Stockholders' Equity (Details 6) (USD $)	0 Months Ended			1 Months Ended					12 Months Ended
	Mar. 04, 2013	Feb. 04, 2013	Oct. 31, 2011	Nov. 30, 2012	Jul. 31, 2012	Jun. 30, 2012	May 31, 2012	Oct. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Jun. 30, 2008
Share Repurchase
Authorized aggregate repurchases of common stock		$ 420,000,000				$ 100,000,000		$ 300,000,000
Period over which shares may be purchased under share repurchase program	1 year		2 years		1 year
Cost of shares repurchased								212,000,000		211,766,000
Cost of shares repurchased				$ 100,000,000			$ 88,000,000		$ 188,000,000
Repurchased shares of common stock				2,000,000			2,000,000	4,700,000
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%