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, 2012
Security
Aug. 31, 2011
May 31, 2012
Security
Maturity Date:      
Due in one year or less, Amortized cost $ 301.8    
Due in one year or less, Fair value 306.3    
Due after one year through three years, Amortized cost 653.6    
Due after one year through three years, Fair value 673.2    
Due after three years through five years, Amortized cost 705.3    
Due after three years through five years, Fair value 731.1    
Due after five years, Amortized cost 1,688.4    
Due after five years, Fair value 1,697.3    
Total, Amortized cost 3,349.1    
Total, Fair value 3,407.9   3,059.0
Funds Held for Clients and Corporate Investments (Textual) [Abstract]      
Separately designated demand deposit account 19.4   13.7
Net unrealized gain on available-for-sale securities 58.8   59.5
Number of available-for-sale securities in an unrealized loss position 34   35
Gross unrealized losses 0.4   0.3
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 0.2 0.1  
Gross realized losses $ 0 $ 0