Taxes (Details) - Schedule of unrecognized tax benefits (USD $) In Millions, unless otherwise specified	12 Months Ended
	May 31, 2014	May 31, 2013	May 31, 2012
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Gross unrecognized benefits, Beginning of period	$ 35.5	$ 38.7	$ 30.8
Decreases related to prior year tax positions	(20.4)	(7.2)	(0.8)
Increase related to prior year tax positions	2.8	3.5	9.5
Increases related to current year tax positions	2.6	1.0	1.7
Settlements during the period	(1.8)	(0.5)	(2.4)
Lapse of statute of limitation	(4.3)	0	(0.1)
Gross unrecognized benefits, End of period	$ 14.4	$ 35.5	$ 38.7