Employee Benefit Plans (Details) - Schedule of net periodic costs (USD $) In Millions, unless otherwise specified	12 Months Ended
	May 31, 2014	May 31, 2013	May 31, 2012
Pension Plans [Member]
Components of net periodic (benefit) cost:
Service cost	$ 0	$ 0	$ 0
Interest cost	7.2	6.9	8.4
Expected return on assets	(12.7)	(10.5)	(10.8)
Net amortization and deferrals	0	0	0
Lump sum settlement charge	1.7	0	0
Recognized net actuarial loss	1.8	2.2	1.4
Net periodic (benefit) cost	(2.0)	(1.4)	(1.0)
Other Postretirement Benefits [Member]
Components of net periodic (benefit) cost:
Service cost	0	0	0
Interest cost	1.3	1.4	1.7
Expected return on assets	0	0	0
Net amortization and deferrals	(0.2)	(0.4)	(0.6)
Lump sum settlement charge	0	0	0
Recognized net actuarial loss	2.2	3.0	3.8
Net periodic (benefit) cost	$ 3.3	$ 4.0	$ 4.9