Annual report pursuant to Section 13 and 15(d)

Description of Business and Significant Accounting Policies (Details)

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Description of Business and Significant Accounting Policies (Details) (USD $)
 12 Months Ended
May 31, 2012
Y
May 31, 2011
May 31, 2010
Description of business and significant accounting policies (Textual) [Abstract]      
Allowance for doubtful accounts $ 1,200,000 $ 2,100,000  
Finite-lived intangible assets, Useful life in years, Minimum 5    
Finite-lived intangible assets, Useful life in years, Maximum 12    
Direct costs billed and incurred 3,300,000,000 3,900,000,000 3,100,000,000
Period in which payroll taxes typically remitted, after receipt of collections from client one to 30 days    
Maximum period payroll taxes remitted, after receipt of collections from client 90 days    
Maximum individual workers' compensation claims liability 1,000,000 1,000,000  
Workers' compensation insurance costs in current liabilities 6,200,000 7,300,000  
Workers compensation insurance costs in long-term liabilities 19,000,000 20,600,000  
Total reserve for uncertain tax positions $ 36,800,000 $ 34,400,000  
Buildings and improvements [Member]
      
Property, Plant and Equipment [Line Items]      
Property and equipment, Useful life in years, Minimum 10    
Property and equipment, Useful life in years, Maximum 35    
Data Processing Equipment [Member]
      
Property, Plant and Equipment [Line Items]      
Property and equipment, Useful life in years, Minimum 2    
Property and equipment, Useful life in years, Maximum 7    
Furniture, fixtures and equipment [Member]
      
Property, Plant and Equipment [Line Items]      
Property and equipment, Useful life in years, Maximum 7    
Leasehold improvements [Member]
      
Property, Plant and Equipment [Line Items]      
Property and equipment, Useful life in years, Maximum 10    
Software development costs [Member]
      
Property, Plant and Equipment [Line Items]      
Property and equipment, Useful life in years, Minimum 3    
Property and equipment, Useful life in years, Maximum 15