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Stock-Based Compensation Plans (Details Textuals) (USD $)
In Millions, unless otherwise specified |
12 Months Ended | 12 Months Ended | 1 Months Ended | 12 Months Ended | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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May 31, 2014
|
May 31, 2013
|
May 31, 2012
|
May 31, 2014
Employee Stock Option [Member]
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May 31, 2013
Employee Stock Option [Member]
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May 31, 2014
Performance Stock Options [Member]
|
May 31, 2013
Performance Stock Options [Member]
|
May 31, 2014
Officer [Member]
Unearned Performance Shares [Member]
|
May 31, 2014
Management [Member]
Restricted Stock Unit [Member]
|
May 31, 2014
Prior to July 2010 [Member]
Officers and Employees [Member]
Employee Stock Option [Member]
|
May 31, 2014
Prior to July 2010 [Member]
Officer [Member]
Restricted Stock [Member]
|
May 31, 2014
Prior to October 2010 [Member]
Director [Member]
Employee Stock Option [Member]
|
May 31, 2014
Beginning in October 2010 [Member]
Director [Member]
Employee Stock Option [Member]
|
May 31, 2014
Beginning in July 2010 [Member]
Officer [Member]
Employee Stock Option [Member]
|
May 31, 2014
Beginning in July 2010 [Member]
Officer [Member]
Restricted Stock [Member]
|
May 31, 2014
October 2006 Broad-based Grant [Member]
Non-management employees [Member]
Employee Stock Option [Member]
|
Jul. 31, 2014
Subsequent Event [Member]
Officer [Member]
Performance Stock Options [Member]
|
May 31, 2014
Achievement of Performance Targets for Fiscal 2014 [Member]
Officer [Member]
Performance Stock Options [Member]
|
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| Stock Based Compensation Plans (Textual) [Abstract] | ||||||||||||||||||
| Number of shares authorized for issuance under stock plan | 39.1 | |||||||||||||||||
| Shares available for future grants | 20.2 | |||||||||||||||||
| Stock-based compensation costs | $ 26.3 | $ 22.8 | $ 22.9 | |||||||||||||||
| Income tax benefits related to stock-based compensation | 10.1 | 8.5 | 8.3 | |||||||||||||||
| Total unrecognized compensation costs related to all unvested stock-based awards | $ 52.4 | |||||||||||||||||
| Weighted-average period in years of all unvested stock-based awards | 2 years 10 months 25 days | |||||||||||||||||
| Contractual life of stock option grants | 10 years | |||||||||||||||||
| Number of days of service needed to be eligible for new hire grant, Non-management employee | 90 days | |||||||||||||||||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||||||||||||||||
| Achievement of performance targets for fiscal 2014 | 23.50% | |||||||||||||||||
| Vesting percentage | 20.00% | 0.00% | 33.00% | 33.00% | 25.00% | 33.00% | 50.00% | |||||||||||
| Performance period for unearned performance shares | 2 years | |||||||||||||||||
| Options outstanding, Ending balance, Shares | 5.4 | 8.0 | 2.8 | 2.7 | 0.4 | |||||||||||||
| Vesting period | 1 year | 5 years | 3 years | 1 year | ||||||||||||||