Stock Repurchase Plan (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Stock Repurchase Plan (Details) [Abstract]
Authorized aggregate amount	$ 1,000,000,000
Total number of shares repurchased since inception of our stock repurchase program (shares)	31,120,279	29,322,753
Aggregate purchase price of shares repurchased since inception of our stock repurchase program	777,300,000	715,500,000
Number of shares repurchased (shares)	1,797,526
Purchase price of shares repurchased	$ 61,900,000