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 6 Months Ended
Nov. 30, 2011
Security
Nov. 30, 2010
Nov. 30, 2011
Security
Nov. 30, 2010
May 31, 2011
Security
Maturity Date:          
Due in one year or less, Amortized cost $ 377.2   $ 377.2    
Due in one year or less, Fair value 381.1   381.1    
Due after one year through three years, Amortized cost 615.5   615.5    
Due after one year through three years, Fair value 637.8   637.8    
Due after three years through five years, Amortized cost 600.8   600.8    
Due after three years through five years, Fair value 621.7   621.7    
Due after five years, Amortized cost 1,103.9   1,103.9    
Due after five years, Fair value 1,110.5   1,110.5    
Total, Amortized cost 2,697.4   2,697.4    
Total, Fair value 2,751.1   2,751.1   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    
Separately designated demand deposit account 10.7   10.7   16.7
Net unrealized gain on available-for-sale securities 53.7   53.7   59.3
Number of available-for-sale securities in an unrealized loss position 28   28   15
Gross unrealized losses (0.3)   (0.3)   (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 0.2 0.2 0.3  
Gross realized losses $ 0 $ 0 $ 0 $ 0