Employee Benefit Plans (Details) - Schedule of net periodic costs (USD $) In Millions, unless otherwise specified	3 Months Ended
	Aug. 31, 2014	Aug. 31, 2013
Components of net periodic benefit (credit) cost:
Amortization of loss	$ 0.7	$ 1.0
Other Pension Plan, Defined Benefit
Components of net periodic benefit (credit) cost:
Service cost	0	0
Interest cost	1.7	1.8
Expected return on assets	(2.5)	(3.1)
Net amortization of prior service credit	0	0
Amortization of loss	0.3	0.4
Net periodic benefit (credit) cost	(0.5)	(0.9)
Other Postretirement Benefit Plan, Defined Benefit
Components of net periodic benefit (credit) cost:
Service cost	0	0
Interest cost	0.3	0.3
Expected return on assets	0	0
Net amortization of prior service credit	0	0
Amortization of loss	0.4	0.6
Net periodic benefit (credit) cost	$ 0.7	$ 0.9