Business Segment Information (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	May 31, 2013	Feb. 28, 2013	Nov. 30, 2012	Aug. 31, 2012	May 31, 2012	Feb. 29, 2012	Nov. 30, 2011	Aug. 31, 2011	May 31, 2013 item	May 31, 2012 item	May 31, 2011 item
Reconciliation of segment gross profit to consolidated income before provision for income taxes
Segment gross profit	$ 60.3	$ 76.2	$ 87.4	$ 90.3	$ 77.4	$ 86.9	$ 78.6	$ 75.7	$ 314.2	$ 318.6	$ 307.1
Selling, general and administrative									(198.4)	(189.4)	(182.7)
Gain on sale of product line											5.9
Earnings from joint ventures									6.8	1.5	3.3
(Loss) gain on extinguishment of debt									(0.3)	(0.7)	0.1
Interest expense									(41.6)	(37.7)	(30.7)
Interest income									1.5	1.2	0.4
Income before provision for income taxes									$ 82.2	$ 93.5	$ 103.4
Non-government customer represents 10% or more of total sales									0	0	0