Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies (Details)

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Commitments and Contingencies (Details) (USD $)
In Millions
3 Months Ended
Aug. 31, 2011
May 31, 2011
Commitments and Contingencies (Textuals) [Abstract]    
Lines of credit outstanding $ 0  
Irrevocable standby letters of credit 47.4 47.4
Irrevocable standby letters of credit outstanding 0  
Expiry date range of letters of credit December 2011 to July 2012  
Commitments to purchase capital assets 10.8 6.0
JP Morgan Chase Bank, N.A. [Member]
   
Lines of credit    
Amount available 350  
Expiration date February 2012  
Bank of America, N.A. [Member]
   
Lines of credit    
Amount available 250  
Expiration date February 2012  
PNC Bank, National Association [Member]
   
Lines of credit    
Amount available 150  
Expiration date February 2012  
Wells Fargo Bank, National Association [Member]
   
Lines of credit    
Amount available $ 150  
Expiration date February 2012