Property and Equipment, Net of Accumulated Depreciation (Components of Property and Equipment, at Cost) (Details) - USD ($) $ in Millions	Aug. 31, 2017	May 31, 2017
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 1,068.1	$ 1,051.0
Less: Accumulated depreciation	739.5	713.8
Property and equipment, net of accumulated depreciation	328.6	337.2
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	103.6	103.5
Data Processing Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	207.8	199.7
Software [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	503.9	496.1
Furniture, Fixtures, and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	115.3	115.2
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	111.5	109.5
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 17.7	$ 18.7