Goodwill and Intangible Assets, Net of Accumulated Amortization (Components of Intangible Assets, at Cost) (Details) - USD ($) $ in Millions	May 31, 2021	May 31, 2020
Intangible Assets [Line Items]
Total intangible assets, gross	$ 656.4	$ 641.7
Less: Accumulated amortization	380.6	311.1
Intangible assets, net of accumulated amortization	275.8	330.6
Other Intangible Assets [Member]
Intangible Assets [Line Items]
Total intangible assets, gross	24.1	23.3
Client Lists [Member]
Intangible Assets [Line Items]
Total intangible assets, gross	$ 632.3	$ 618.4