Consolidated Balance Sheets (Parenthetical) - $ / shares	Aug. 31, 2017	May 31, 2017
Stockholders' equity
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	600,000,000	600,000,000
Common stock, shares issued	358,900,000	359,400,000
Common stock, shares outstanding	358,900,000	359,400,000