Business Segment Information (Details 4) (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	May 31, 2012	May 31, 2011
Business Segment Information
Long-lived assets	$ 1,103.2				$ 1,132.4				$ 1,103.2	$ 1,132.4
Sales	553.8	520.2	512.8	550.5	563.3	534.2	482.0	485.5	2,137.3	2,065.0	1,805.1
United States
Business Segment Information
Long-lived assets	834.1				882.4				834.1	882.4
Europe
Business Segment Information
Long-lived assets	267.2				248.4				267.2	248.4
Other
Business Segment Information
Long-lived assets	1.9				1.6				1.9	1.6
Foreign countries
Business Segment Information
Sales									$ 656.5	$ 435.7	$ 330.2
Foreign countries | Total sales | Geographic concentration
Business Segment Information
Percentage of total sales									30.70%	21.10%	18.30%