Legal Proceedings and Contingent Liabilities - Employee Exposure Standards by Regulatory Agencies (Details) (Maximum)	12 Months Ended
	May 31, 2013
Occupational Safety And Health Administration
Loss Contingencies [Line Items]
Employee exposure standards, nanograms per cubic meter	5,000
National Institute For Occupational Safety And Health
Loss Contingencies [Line Items]
Employee exposure standards, nanograms per cubic meter	1,000
California Environmental Protection Agency
Loss Contingencies [Line Items]
Employee exposure standards, nanograms per cubic meter	200