Property, Plant and Equipment (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Feb. 29, 2020	May 31, 2020	May 31, 2019	May 31, 2018
Property, Plant and Equipment [Line Items]
Total at cost		$ 996.9	$ 948.3
Less: Accumulated depreciation and amortization		420.0	370.6
Property, plant and equipment, net		576.9	577.7
Asset impairments and write downs	$ 40.0	40.6	0.9	$ 11.2
Depreciation and amortization expense		60.5	56.2	41.8
Assets Held-for-sale, Not Part of Disposal Group		8.8
Land [Member]
Property, Plant and Equipment [Line Items]
Total at cost		82.5	79.1
Building [Member]
Property, Plant and Equipment [Line Items]
Total at cost		246.7	239.1
Capitalized software [Member]
Property, Plant and Equipment [Line Items]
Total at cost		189.5	158.9
Furniture, fixtures and equipment [Member]
Property, Plant and Equipment [Line Items]
Total at cost		217.0	213.4
Building and Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Total at cost		212.2	211.0
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Total at cost		49.0	46.8
Website Development [Member]
Property, Plant and Equipment [Line Items]
Asset impairments and write downs				11.0
Book Fair Trucks [Member]
Property, Plant and Equipment [Line Items]
Asset impairments and write downs				$ 0.2
Legacy Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Asset impairments and write downs		$ 0.6	$ 0.9