Quarterly report pursuant to Section 13 or 15(d)

Funds Held for Clients and Corporate Investments (Details 1)

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Funds Held for Clients and Corporate Investments (Details 1) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Aug. 31, 2011
Aug. 31, 2010
May 31, 2011
Maturity Date:      
Due in one year or less, Amortized cost $ 428.8    
Due in one year or less, Fair value 434.4    
Due after one year through three years, Amortized cost 614.5    
Due after one year through three years, Fair value 641.1    
Due after three years through five years, Amortized cost 547.9    
Due after three years through five years, Fair value 575.0    
Due after five years, Amortized cost 634.0    
Due after five years, Fair value 644.4    
Total, Amortized cost 2,225.2    
Total, Fair value 2,294.9   2,737.2
Funds Held for Clients and Corporate Investments (Textuals) [Abstract]      
Maturity period of municipal bonds included in cash equivalents less than 90 days    
Net unrealized gain on available-for-sale securities 69.7   59.3
Number of available-for-sale securities in an unrealized loss position 10   15
Fair value of available-for-sale securities in an unrealized loss position 25.2    
Gross unrealized losses 0   0.1
Minimum maturity period for VRDNs, primarily categorized as due after five years (in years) 20 years    
Maximum maturity period for VRDNs, primarily categorized as due after five years (in years) 30 years    
Gross realized gains 0.1 0.1  
Gross realized losses $ 0 $ 0