Goodwill and Intangible Assets, Net of Accumulated Amortization (Components of Intangible Assets, at Cost) (Details) - USD ($) $ in Millions	May 31, 2016	May 31, 2015
Finite-Lived Intangible Assets [Line Items]
Total intangible assets, gross	$ 294.6	$ 247.8
Less: Accumulated amortization	225.1	215.4
Intangible assets, net of accumulated amortization	69.5	32.4
Client Lists [Member]
Finite-Lived Intangible Assets [Line Items]
Total intangible assets, gross	289.2	244.6
Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Total intangible assets, gross	$ 5.4	$ 3.2