Goodwill and Intangible Assets, Net of Accumulated Amortization (Components of Intangible Assets, at Cost) (Details) - USD ($) $ in Millions	Aug. 31, 2019	May 31, 2019
Intangible Assets [Line Items]
Total intangible assets, gross	$ 632.4	$ 631.2
Less: Accumulated amortization	252.9	232.1
Intangible assets, net of accumulated amortization	379.5	399.1
Other Intangible Assets [Member]
Intangible Assets [Line Items]
Total intangible assets, gross	23.4	23.0
Client Lists [Member]
Intangible Assets [Line Items]
Total intangible assets, gross	$ 609.0	$ 608.2