Annual report pursuant to Section 13 and 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
 12 Months Ended
May 31, 2011
May 31, 2010
May 31, 2009
Realized gains and losses on the sales of available-for-sale securities      
Gross realized gains $ 1.3 $ 3.2 $ 1.2
Gross realized losses     (0.1)
Net realized gains 1.3 3.2 1.1
Maturity Date:      
Due in one year or less, Amortized cost 408.7    
Due in one year or less, Fair value 412.3    
Due after one year through three years, Amortized cost 603.0    
Due after one year through three years, Fair value 626.9    
Due after three years through five years, Amortized cost 570.8    
Due after three years through five years, Fair value 592.7    
Due after five years, Amortized cost 1,095.4    
Due after five years, Fair value 1,105.3    
Total, Amortized cost 2,677.9    
Total, Fair value 2,737.2    
Funds Held for Clients and Corporate Investments (Textuals) [Abstract]      
Net unrealized gain on available-for-sale securities 59.3 66.6  
Number of available-for-sale securities in an unrealized loss position 15 23  
Available-for-sale securities having fair value lower than amortized cost 51.7 73.6  
Gross unrealized losses $ 0.1 $ 0.4  
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