Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	May 31, 2014	May 31, 2013	May 31, 2012
Operating Leased Assets [Line Items]
Operating lease expense	$ 27.6	$ 32.9	$ 38.9
Capital lease amortization expense	0.8	1.1	1.1
Open standby letters of credit	$ 5.3	$ 6.6
Minimum [Member]
Operating Leased Assets [Line Items]
Operating lease period	1 year
Maximum [Member]
Operating Leased Assets [Line Items]
Operating lease period	40 years