Business Segment Information (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	May 31, 2014	Feb. 28, 2014	Nov. 30, 2013	Aug. 31, 2013	May 31, 2013	Feb. 28, 2013	Nov. 30, 2012	Aug. 31, 2012	May 31, 2014	May 31, 2013	May 31, 2012
Reconciliation of segment gross profit to consolidated income before provision for income taxes
Segment gross profit	$ 85.8	$ 78.7	$ 91.0	$ 84.7	$ 60.3	$ 76.2	$ 87.4	$ 90.3	$ 340.2	$ 314.2	$ 318.6
Selling, general and administrative									(197.6)	(198.4)	(189.4)
Earnings from joint ventures									3.1	6.8	1.5
Loss on extinguishment of debt										(0.3)	(0.7)
Interest expense									(42.0)	(41.6)	(37.7)
Interest income									1.6	1.5	1.2
Income before provision for income taxes									$ 105.3	$ 82.2	$ 93.5