Annual report pursuant to Section 13 and 15(d)

Property and Equipment, Net of Accumulated Depreciation (Components of Property and Equipment, at Cost) (Details)

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Property and Equipment, Net of Accumulated Depreciation (Components of Property and Equipment, at Cost) (Details) - USD ($)
$ in Millions
 12 Months Ended
May 31, 2017
May 31, 2016
May 31, 2015
Property, Plant and Equipment [Line Items]      
Total property and equipment, gross $ 1,051.0 $ 1,012.2  
Less: Accumulated depreciation 713.8 659.2  
Property and equipment, net of accumulated depreciation 337.2 353.0  
Depreciation expense 108.8 99.2 $ 92.1
Land and Improvements [Member]      
Property, Plant and Equipment [Line Items]      
Total property and equipment, gross 8.3 8.3  
Buildings and Improvements [Member]      
Property, Plant and Equipment [Line Items]      
Total property and equipment, gross 103.5 103.0  
Data Processing Equipment [Member]      
Property, Plant and Equipment [Line Items]      
Total property and equipment, gross 199.7 196.1  
Software [Member]      
Property, Plant and Equipment [Line Items]      
Total property and equipment, gross [1] 496.1 447.5  
Furniture, Fixtures, and Equipment [Member]      
Property, Plant and Equipment [Line Items]      
Total property and equipment, gross 115.2 125.0  
Leasehold Improvements [Member]      
Property, Plant and Equipment [Line Items]      
Total property and equipment, gross 109.5 108.2  
Construction in Progress [Member]      
Property, Plant and Equipment [Line Items]      
Total property and equipment, gross [1] $ 18.7 $ 24.1  
[1] Software includes both purchased software and costs capitalized related to internally developed software placed in service. Capitalized costs related to internally developed software that has not yet been placed in service is included in construction in progress.