Employee Benefit Plans (Detail) - Schedule Of Net Benefit Costs (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Feb. 29, 2012	Feb. 28, 2011	Feb. 29, 2012	Feb. 28, 2011
Pension Plans, Defined Benefit [Member]
Service cost		$ 0.1		$ 0.2
Interest cost	2.1	2.2	6.3	6.6
Expected return on assets	(2.7)	(2.3)	(8.1)	(7.0)
Amortization of loss	0.3	0.3	1.0	1.4
Settlement of Canadian plan		0.2		3.6
Net periodic benefit (credit) costs	(0.3)	0.5	(0.8)	4.8
Other Postretirement Benefit Plans, Defined Benefit [Member]
Service cost	0	0	0	0
Interest cost	0.4	0.5	1.4	1.4
Net amortization of prior service credit	(0.2)	(0.2)	(0.5)	(0.5)
Amortization of loss	0.9	0.7	2.9	1.9
Net periodic benefit (credit) costs	$ 1.1	$ 1.0	$ 3.8	$ 2.8