Employee Benefit Plans (Details) - Schedule of effect of one percentage point change in assumed health care cost trend rates (USD $) In Millions, unless otherwise specified	12 Months Ended
	May 31, 2013	May 31, 2012
Schedule of effect of one percentage point change in assumed health care cost trend rates [Abstract]
Total service and interest cost - 1% increase	$ 0.2	$ 0.2
Total service and interest cost - 1% decrease	(0.1)	(0.2)
Post-retirement benefit obligation - 1% increase	4.0	4.3
Post-retirement benefit obligation - 1% decrease	$ (3.4)	$ (3.7)