Gross Accounts Receivable from Significant Customers as Percentage of Total Consolidated Gross Accounts Receivable (Detail) (Accounts Receivable, Customer Concentration Risk)	May 31, 2013	May 31, 2012
Chrysler
Concentration Risk [Line Items]
Percentage of Consolidated Gross Accounts Receivable	22.00%	18.00%
Ford
Concentration Risk [Line Items]
Percentage of Consolidated Gross Accounts Receivable	6.00%	8.00%
U.S. Steel
Concentration Risk [Line Items]
Percentage of Consolidated Gross Accounts Receivable	6.00%	5.00%