Quarterly report pursuant to Section 13 or 15(d)

Funds Held for Clients and Corporate Investments (Details 2)

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Funds Held for Clients and Corporate Investments (Details 2) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Aug. 31, 2013
Security
Aug. 31, 2012
May 31, 2013
Security
Maturity Date:      
Due in one year or less, Amortized cost $ 339.6    
Due in one year or less, Fair value 343.0    
Due after one year through three years, Amortized cost 711.8    
Due after one year through three years, Fair value 727.0    
Due after three years through five years, Amortized cost 704.1    
Due after three years through five years, Fair value 705.8    
Due after five years, Amortized cost 1,561.2    
Due after five years, Fair value 1,532.7    
Total, Amortized cost 3,316.7    
Fair value 3,308.5   3,691.4
Funds Held for Clients and Corporate Investments (Textual)      
Maximum maturity on short-term investments classified as cash equivalents 90 days    
Separately Designated Demand Deposit Account 22.2   23.4
Net unrealized gain (loss) on available-for-sale securities (8.2)   34.7
Number of available-for-sale securities in an unrealized loss position 335   147
Gross realized gains 0.2 0.2  
Gross realized losses $ 0 $ 0  
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