Common Stock (Details) (Textuals) (USD $) In Millions, except Per Share data	9 Months Ended		12 Months Ended	9 Months Ended		9 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010	Sep. 30, 2011 Common stock under accelerated share repurchase agreement [Member]	May 27, 2011 Common stock under accelerated share repurchase agreement [Member]	Sep. 30, 2011 Common stock under existing stock repurchase program [Member]	Sep. 30, 2011 ASR Agreement 1 [Member]	Sep. 30, 2011 ASR Agreement 1 [Member]	Sep. 30, 2011 ASR Agreement 2 [Member]
Equity, Class of Treasury Stock [Line Items]
Number of common shares repurchased	44.3		26.9	29.4		13.0
Purchase price of common stock				$ 59.53
Repurchase of common stock agreement	$ 2,515.7	$ 1,276.2		$ 1,750.0		$ 765.7		$ 1,000.0	$ 750.0
Accelerated Share Repurchase, shares to be received from investment bank	1.8								1.8
Final forward price of common stock							$ 53.51
Maximum number of shares to be received under ASR					58.8
Additional shares of common stock							1.9
Fair value of equity instruments, forward stock purchase contracts				Deemed to have a fair value of zero at the effective date
Common Stock (Textuals) [Abstract]
Increase in authorization for repurchase of shares under stock repurchase program	50