Quarterly report pursuant to Section 13 or 15(d)

Shareholders' Equity (Details Textual)

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Shareholders' Equity (Details Textual) (USD $)
Share data in Millions, except Per Share data, unless otherwise specified
1 Months Ended 3 Months Ended 6 Months Ended
Jul. 31, 2012
Apr. 30, 2012
Feb. 29, 2012
Jun. 30, 2012
Mar. 31, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Jul. 27, 2012
May 30, 2012
May 02, 2012
Mar. 22, 2012
Shareholders' Equity (Textual) [Abstract]                        
Cash dividends per common share   $ 0.30 $ 0.30                  
Aggregate amount of cash dividend paid                   $ 35,100,000   $ 35,200,000
Dividends and dividend equivalents       (35,100,000)   (23,900,000) (70,310,000) (38,689,000)        
Share repurchase program capacity authorization       1,000,000,000     1,000,000,000   1,000,000,000      
Share repurchase program, remaining authorized capacity       188,900,000     188,900,000       427,900,000  
Repurchase of common stock share 3.9     5.3 0.7              
Share repurchased through open market purchases, Aggregate cost       $ 239,000,000 $ 50,000,000              
Average cost per share of share repurchased       $ 45.05 $ 67.24