Consolidated Condensed Balance Sheets (Unaudited) (Parenthetical) (USD $)	Feb. 28, 2013	May 31, 2012
Statement of Financial Position [Abstract]
Preferred stock, no par value (in dollars per share)	$ 0	$ 0
Preferred stock, shares authorized (in shares)	100,000	100,000
Preferred stock, shares outstanding ( in shares)	0	0
Common stock, no par value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized (in shares)	425,000,000	425,000,000
Common stock, shares issued (in shares)	174,570,683	173,745,913
Common stock, shares outstanding (in shares)	122,723,896	126,519,758
Treasury stock, shares (in shares)	51,846,787	47,226,155