Share Repurchases (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Share Repurchases [Line Items]
Shares repurchased	4,053,527
Average price per share for repurchased shares (in dollars per share)	$ 72.02
Number of treasury shares held	83,455,112	79,401,585
Number of common stock shares repurchased in open market subsequent to period end	126,319
May 2012 Authorization [Member]
Share Repurchases [Line Items]
Number of shares authorized to be repurchased	10,000,000
Remaining number of shares authorized to be repurchased	3,908,289
November 2012 Authorization [Member]
Share Repurchases [Line Items]
Shares repurchased	4,047,576
Authorized dollar amount for share repurchase program	$ 1,000,000,000
Remaining dollar amount authorized to be repurchased	$ 458,465,000
Shares repurchased in open market [Member]
Share Repurchases [Line Items]
Shares repurchased	4,047,576
Shares repurchased from holders of employee stock options [Member]
Share Repurchases [Line Items]
Shares repurchased	5,951