Property, Plant and Equipment (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	May 31, 2016	May 31, 2018	May 31, 2017	May 31, 2016
Property, Plant and Equipment [Line Items]
Total at cost		$ 895.8	$ 920.8
Less: Accumulated depreciation and amortization		(340.2)	(445.5)
Property, plant and equipment, net		555.6	475.3
Depreciation and amortization expense of property plant and equipment		41.8	36.2	$ 36.7
Asset impairments		11.2	6.8	14.4
Land [Member]
Property, Plant and Equipment [Line Items]
Total at cost		78.9	77.5
Building [Member]
Property, Plant and Equipment [Line Items]
Total at cost		240.0	239.7
Capitalized software [Member]
Property, Plant and Equipment [Line Items]
Total at cost		158.7	202.0
Furniture, fixtures and equipment [Member]
Property, Plant and Equipment [Line Items]
Total at cost		215.5	224.7
Building and Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Total at cost		202.7	176.9
Property capitalized		99.6	$ 34.2
Property capitalized not yet being depreciated		59.3
Book Fairs Trucks [Member]
Property, Plant and Equipment [Line Items]
Asset impairments	$ 0.2
Website Development [Member]
Property, Plant and Equipment [Line Items]
Asset impairments		$ 5.7
Legacy Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Asset impairments	$ 11.0			$ 7.5