Capital Stock (Details Textual) (USD $) Share data in Millions, unless otherwise specified	1 Months Ended	3 Months Ended		6 Months Ended
	Oct. 31, 2006	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Capital Stock (Textual) [Abstract]
Share Repurchase Program	$ 1,000,000,000
Repurchase of shares of common stock		1.1	0	3.3	0
Aggregate cost of repurchase		24,600,000		73,600,000
Aggregate number of shares repurchased		6.8		6.8
Shares repurchased aggregate value		504,300,000		504,300,000
Number of shares repurchased under settlement of employee tax withholding obligations				0.1	0.1
Shares repurchased aggregate value under settlement of employee tax withholding obligations				$ 3,200,000	$ 5,400,000