Employee Benefit Plans (Detail) - Schedule of net periodic costs (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Feb. 28, 2013	Feb. 29, 2012	Feb. 28, 2013	Feb. 29, 2012
Pension Plans, Defined Benefit [Member]
Interest cost	$ 1.7	$ 2.1	$ 5.2	$ 6.3
Expected return on assets	(2.6)	(2.7)	(7.9)	(8.1)
Amortization of (gain) loss	0.5	0.3	1.6	1.0
Net periodic benefit (credit) cost	(0.4)	(0.3)	(1.1)	(0.8)
Other Postretirement Benefit Plans, Defined Benefit [Member]
Service cost	0	0	0	0
Interest cost	0.3	0.4	1.1	1.4
Net amortization of prior service credit	(0.1)	(0.2)	(0.3)	(0.5)
Amortization of (gain) loss	0.3	0.9	2.2	2.9
Net periodic benefit (credit) cost	$ 0.5	$ 1.1	$ 3.0	$ 3.8