Employee Benefit Plans (Details) - Schedule of net periodic costs (USD $) In Millions, unless otherwise specified	12 Months Ended
	May 31, 2013	May 31, 2012	May 31, 2011
Pension Plan, Defined Benefit [Member]
Components of net periodic (benefit) cost:
Service cost			$ 0.3
Interest cost	6.9	8.4	8.9
Expected return on assets	(10.5)	(10.8)	(9.4)
Settlement			4.2
Recognized net actuarial loss	2.2	1.4	1.8
Net periodic (benefit) cost	(1.4)	(1.0)	5.8
Other Postretirement Benefit Plan, Defined Benefit [Member]
Components of net periodic (benefit) cost:
Service cost	0	0
Interest cost	1.4	1.7	1.9
Net amortization and deferrals	(0.4)	(0.6)	(0.7)
Recognized net actuarial loss	3.0	3.8	2.6
Net periodic (benefit) cost	$ 4.0	$ 4.9	$ 3.8