Common Stock (Details Textual) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended					3 Months Ended		12 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Common stock under accelerated share repurchase agreement [Member]	May 27, 2011 Common stock under accelerated share repurchase agreement [Member]	Jun. 30, 2011 Common stock under existing stock repurchase program [Member]	Sep. 30, 2011 ASR Agreement 1 [Member]	Dec. 31, 2011 ASR Agreement 1 [Member]	Dec. 31, 2011 ASR Agreement 2 [Member]	Dec. 31, 2011 ASR Agreement 2 [Member]
Equity, Class of Treasury Stock [Line Items]
Number of common shares repurchased	46,400,000	26,900,000		29,400,000		13,000,000
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									100,000	100,000
Final forward price of common stock							$ 53.51		$ 50.69
Maximum number of shares to be received under ASR					58,800,000
Additional shares of common stock				4,000,000			1,900,000		2,100,000
Fair value of equity instruments, forward stock purchase contracts				Deemed to have a fair value of zero at the effective date
Common Stock (Textual) [Abstract]
Increase in authorization for repurchase of shares under stock repurchase program	50,000,000
Number of additional share of common stock issued for each share of common stock outstanding		1
Share issued in common stock offering			52,900,000
Common stock shares sold as result of underwriter's exercise of overallotment option			6,900,000
Underwriter's exercise of common stock over allotment option in full at closing, per share			$ 30.50
Net proceeds resulting from public offering of common stock			1,569.1
Underwriting discount and issuance costs of common stock			44.4
Shares remaining under share repurchase program	18,700,000
Treasury stock reissued in connection with employee compensation plans	44,100,000
Common stock reserved for employee benefit plans	36,800,000
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Date	March 15,2011
Settled portion of total agreement	$ 725.0