Property and Equipment, Net of Accumulated Depreciation (Components of Property and Equipment, at Cost) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Feb. 28, 2017	Feb. 29, 2016	Feb. 28, 2017	Feb. 29, 2016	May 31, 2016
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 1,032.2		$ 1,032.2		$ 1,012.2
Less: Accumulated depreciation	690.6		690.6		659.2
Property and equipment, net of accumulated depreciation	341.6		341.6		353.0
Depreciation expense	26.4	$ 25.1	77.2	$ 73.8
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	103.3		103.3		103.0
Data Processing Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	196.7		196.7		196.1
Software [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	475.4		475.4		447.5
Furniture, Fixtures, and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	113.6		113.6		125.0
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	108.6		108.6		108.2
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 26.3		$ 26.3		$ 24.1