Employee Benefit Plans (Detail) - Schedule of net periodic costs (USD $) In Millions, unless otherwise specified	3 Months Ended
	Aug. 31, 2012	Aug. 31, 2011
Pension Plans, Defined Benefit [Member]
Components of net periodic benefit (credit) cost:
Interest cost	$ 1.7	$ 2.1
Expected return on assets	(2.6)	(2.7)
Amortization of loss	0.5	0.3
Net periodic benefit (credit) cost	(0.4)	(0.3)
Other Postretirement Benefit Plans, Defined Benefit [Member]
Components of net periodic benefit (credit) cost:
Service cost	0	0
Interest cost	0.4	0.5
Net amortization of prior service credit	(0.1)	(0.2)
Amortization of loss	0.9	1.0
Net periodic benefit (credit) cost	$ 1.2	$ 1.3