Income Taxes (Details 3) - USD ($) $ in Millions	12 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2013
Reconciliation of gross unrecognized tax benefits
Balance as of beginning of fiscal year	$ 40.0	$ 26.7	$ 41.7
Additions for tax positions of the current year	6.7	11.2	28.5
Additions for tax positions of prior years	0.8	4.2	12.2
Reductions for tax positions of prior years	(0.4)	(1.8)	(0.5)
Settlements with tax authorities	(1.2)	0.0	(55.0)
Expiration of the statute of limitations	(6.0)	(0.3)	(0.2)
Balance as of end of fiscal year	$ 39.9	$ 40.0	$ 26.7