Goodwill and Intangible Assets, Net of Accumulated Amortization (Components of Intangible Assets, at Cost) (Details) - USD ($) $ in Millions	May 31, 2020	May 31, 2019
Intangible Assets [Line Items]
Total intangible assets, gross	$ 641.7	$ 631.2
Less: Accumulated amortization	311.1	232.1
Intangible assets, net of accumulated amortization	330.6	399.1
Other Intangible Assets [Member]
Intangible Assets [Line Items]
Total intangible assets, gross	23.3	23.0
Client Lists [Member]
Intangible Assets [Line Items]
Total intangible assets, gross	$ 618.4	$ 608.2