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Stock Based Compensation Plans (Details Textuals) (USD $)
In Millions, unless otherwise specified |
12 Months Ended | 12 Months Ended | ||||||||||||||||||
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May 31, 2011
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May 31, 2010
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May 31, 2009
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May 31, 2011
Employee Stock Option [Member]
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May 31, 2010
Employee Stock Option [Member]
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May 31, 2009
Employee Stock Option [Member]
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May 31, 2008
Employee Stock Option [Member]
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May 31, 2011
Stock Incentive Plan 1998 [Member]
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May 31, 2011
Officers And Board [Member]
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May 31, 2011
Officers and employees non-qualified stock options granted prior to July 2010 [Member]
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May 31, 2011
Officers non-qualified stock options granted beginning in July 2010 [Member]
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May 31, 2011
Board non-qualified stock options granted prior to October 2010 [Member]
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May 31, 2011
Board non-qualified stock options granted beginning in October 2010 [Member]
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May 31, 2011
Newly-hired employees stock option grants [Member]
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May 31, 2011
Officers restricted stock awards granted prior to July 2010 [Member]
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May 31, 2011
Officers restricted stock awards granted beginning in July 2010 [Member]
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May 31, 2011
Board restricted stock awards granted prior to October 2010 [Member]
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May 31, 2011
Board restricted stock awards granted beginning in October 2010 [Member]
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May 31, 2011
Restricted Stock Unit [Member]
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May 31, 2011
Performance shares vesting after performance period [Member]
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||||||||||||||||||
| Number of options outstanding | 12.5 | 14.2 | 14.0 | 14.3 | 1.0 | |||||||||||||||
| Vesting schedule | 20% per annum | 25% per annum | one-third per annum | After one year | 20% per annum | fifth anniversary | one-third per annum | third anniversary | one-year anniversary | 20% per annum with a small population of awards vesting on fourth-anniversary of grant date | one year | |||||||||
| Performance period for unearned performance shares | 2 years | |||||||||||||||||||
| Stock Based Compensation Plans (Textuals) [Abstract] | ||||||||||||||||||||
| Number of shares authorized for issuance under stock plan | 39.1 | |||||||||||||||||||
| Shares available for future grants | 24.8 | |||||||||||||||||||
| Stock-based compensation expense | $ 24.8 | $ 25.6 | $ 25.7 | |||||||||||||||||
| Income tax benefits | 8.4 | 7.9 | 8.0 | |||||||||||||||||
| Total unrecognized compensation cost related to all unvested stock-based awards | $ 36.9 | |||||||||||||||||||
| Weighted average period of all unvested stock based awards | 2.7 | |||||||||||||||||||
| No of days of service to be eligible to receive grant of options for non-management employees | 90 days | |||||||||||||||||||
| Contractual life of stock option grants | 10 years | |||||||||||||||||||