Earnings per Share (Narrative) (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	12 Months Ended				0 Months Ended	2 Months Ended		12 Months Ended	20 Months Ended
	May 31, 2013	May 31, 2012	May 31, 2011	May 31, 2013 Employee payroll taxes due on restricted stock [Member]	Oct. 18, 2011 Common Stock [Member]	May 31, 2012 Common Stock [Member]	Jul. 29, 2011 Common Stock [Member]	May 31, 2013 Common Stock [Member]	Jun. 30, 2013 Common Stock [Member]
Earnings Per Share, Basic and Diluted [Line Items]
Options granted excluded from the computation of diluted earnings per share (shares)	0.7	2.0	3.9
Common stock purchased under a share buyback program (shares)				0.2		3.3	8.1	5.1	8.6
Aggregate purchase price of common stock under a share buyback program				$ 7,700,000		$ 129,600,000	$ 259,500,000	$ 208,000,000	$ 348,900,000
Additional amount authorized under share buyback program					$ 500,000,000
Average price of common stock purchased under a share buyback program (dollars per share)				$ 38.04				$ 40.97	$ 40.43