Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation Plans (Details Textual)

v2.4.0.6
Stock-Based Compensation Plans (Details Textual) (USD $)
In Millions, except Share data, unless otherwise specified
12 Months Ended
May 31, 2012
Y
May 31, 2011
May 31, 2010
Stock Based Compensation Plans (Textual) [Abstract]      
Number of shares authorized for issuance under stock plan 39,100,000    
Shares available for future grants 23,400,000    
Stock based compensation expenses $ 22.9 $ 24.8 $ 25.6
Income tax benefits 8.3 8.4 7.9
Total unrecognized compensation cost related to all unvested stock-based awards 43.8    
Weighted-average period in years of all unvested stock based awards 2.9    
No days service to be eligible for new hire grant non management employee 90 days    
Contractual life of stock option grants 10 years    
Number of shares to be received by restricted stock unit holders for each unit granted 1    
Stock Incentive Plan 1998 [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of options outstanding 100,000    
Officers and employees non-qualified stock options granted prior to July 2010 [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting schedule 20% per annum    
Officers non-qualified stock options granted beginning in July 2010 [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting schedule 25% per annum    
Board non-qualified stock options granted prior to October 2010 [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting schedule one-third per annum    
Board non-qualified stock options granted beginning in October 2010 [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting schedule After one year    
Officers restricted stock awards granted prior to July 2010 [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting schedule fifth anniversary    
Officers restricted stock awards granted beginning in July 2010 [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting schedule one-third per annum    
Board restricted stock awards granted prior to October 2010 [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting schedule third anniversary    
Board restricted stock awards granted beginning in October 2010 [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting schedule one-year anniversary    
Restricted Stock Unit [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting schedule 20% per annum with a small population of awards vesting on fourth-anniversary of grant date    
Total grant-date fair value of restricted stock vested 9.5 8.5 6.6
Unearned Performance Shares [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting schedule one year    
Performance period for unearned performance shares 2 years    
Performance Stock Options [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of options outstanding 2,600,000     
Vesting schedule The awards will vest in full if performance targets for the fiscal year ended May 31, 2016 are achieved. Acceleration of vesting for up to one-half of the award will occur if performance targets for the fiscal year ending May 31, 2014 are achieved. There also is an opportunity to vest in one-half of the award at threshold performance, which is 95% of target.    
Restricted stock [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total grant-date fair value of restricted stock vested $ 3.2 $ 2.2 $ 0.3