Goodwill and Intangible Assets, Net of Accumulated Amortization (Components of Intangible Assets, at Cost) (Details) - USD ($) $ in Millions		Feb. 28, 2018	May 31, 2017
Finite-Lived Intangible Assets [Line Items]
Total intangible assets, gross		$ 314.1	$ 298.9
Less: Accumulated amortization		209.0	241.3
Intangible assets, net of accumulated amortization		105.1	57.6
Client Lists [Member]
Finite-Lived Intangible Assets [Line Items]
Total intangible assets, gross	[1]	308.4	293.5
Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Total intangible assets, gross		$ 5.7	$ 5.4

[1] Client lists include current estimates of amounts acquired from Lessor as of February 28, 2018. Refer to Note C for further details.