Goodwill and Intangible Assets, Net of Accumulated Amortization (Components of Intangible Assets, at Cost) (Details) - USD ($) $ in Millions	Feb. 29, 2020	May 31, 2019
Intangible Assets [Line Items]
Total intangible assets, gross	$ 640.0	$ 631.2
Less: Accumulated amortization	292.0	232.1
Intangible assets, net of accumulated amortization	348.0	399.1
Other Intangible Assets [Member]
Intangible Assets [Line Items]
Total intangible assets, gross	23.2	23.0
Client Lists [Member]
Intangible Assets [Line Items]
Total intangible assets, gross	$ 616.8	$ 608.2