Income Taxes (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
	May 31, 2012	May 31, 2011	May 31, 2010
Reconciliation of gross unrecognized tax benefits, not including interest or potential offsetting effects
Balance as of beginning of fiscal year	$ 41.2	$ 35.8	$ 35.8
Additions for tax positions of the current year	0.4	6.0	0.5
Additions for tax positions of prior years	1.3	0.1
Reductions for tax positions of prior years	(0.1)	(0.1)
Settlements with tax authorities	(0.7)
Expiration of the statute of limitations	(0.4)	(0.6)	(0.5)
Balance as of end of fiscal year	$ 41.7	$ 41.2	$ 35.8