Stock-Based Compensation - Weighted Average Assumptions Used to Estimate Fair Values (Detail) (Stock Incentive Plan 1990, Class B Common Stock)	3 Months Ended
	Aug. 31, 2014	Aug. 31, 2013
Stock Incentive Plan 1990 | Class B Common Stock
Common Stock and Share Based Compensation [Line Items]
Dividend yield	1.20%	1.30%
Expected volatility	23.60%	27.90%
Weighted average expected life (in years)	5 years 9 months 18 days	5 years 3 months 18 days
Risk-free interest rate	1.70%	1.30%