Share Repurchases (Details) (USD $)	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Share Repurchases [Line Items]
Document Period End Date	Sep. 30, 2012
Document Fiscal Period Focus	Q3
Shares repurchased	6,635,627
Average price per share for repurchased shares (in dollars per share)	$ 59.28
Number of treasury shares held	73,636,114	67,000,487
Number of common stock shares repurchased in open market subsequent to period end	900,000
May 2012 Authorization [Member]
Share Repurchases [Line Items]
Number of shares authorized to be repurchased	10,000,000
Shares repurchased	4,292,804
Remaining number of shares authorized to be repurchased	5,707,196
Shares repurchased in open market [Member]
Share Repurchases [Line Items]
Shares repurchased	6,552,804
Shares repurchased from holders of employee stock options [Member]
Share Repurchases [Line Items]
Shares repurchased	82,823