Quarterly report pursuant to Section 13 or 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
 3 Months Ended 6 Months Ended
Nov. 30, 2016
Nov. 30, 2015
Nov. 30, 2016
Nov. 30, 2015
May 31, 2016
Property, Plant and Equipment [Line Items]          
Total property and equipment, gross $ 1,024.9   $ 1,024.9   $ 1,012.2
Less: Accumulated depreciation 675.6   675.6   659.2
Property and equipment, net of accumulated depreciation 349.3   349.3   353.0
Depreciation expense 25.5 $ 24.7 50.8 $ 48.7  
Land and Improvements [Member]          
Property, Plant and Equipment [Line Items]          
Total property and equipment, gross 8.3   8.3   8.3
Buildings and Improvements [Member]          
Property, Plant and Equipment [Line Items]          
Total property and equipment, gross 103.1   103.1   103.0
Data Processing Equipment [Member]          
Property, Plant and Equipment [Line Items]          
Total property and equipment, gross 197.9   197.9   196.1
Software [Member]          
Property, Plant and Equipment [Line Items]          
Total property and equipment, gross 468.0   468.0   447.5
Furniture, Fixtures, and Equipment [Member]          
Property, Plant and Equipment [Line Items]          
Total property and equipment, gross 113.7   113.7   125.0
Leasehold Improvements [Member]          
Property, Plant and Equipment [Line Items]          
Total property and equipment, gross 109.0   109.0   108.2
Construction in Progress [Member]          
Property, Plant and Equipment [Line Items]          
Total property and equipment, gross $ 24.9   $ 24.9   $ 24.1