Goodwill and Intangible Assets, Net of Accumulated Amortization (Details) (USD $) In Millions, unless otherwise specified	Aug. 31, 2013	May 31, 2013
Components of intangible assets, at cost
Client lists	$ 231.4	$ 231.0
Other intangible assets	2.4	2.4
Total intangible assets, gross	233.8	233.4
Less: Accumulated amortization	191.7	188.2
Intangible assets, net of accumulated amortization	42.1	45.2
Estimated future amortization expense relating to intangible assets
Fiscal year ending May 31, 2014	14.9
Fiscal year ending May 31, 2015	10.9
Fiscal year ending May 31, 2016	7.8
Fiscal year ending May 31, 2017	5.5
Fiscal year ending May 31, 2018	$ 3.6