Retirement Plans (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
	May 31, 2011	May 31, 2010
Defined Benefit Plan Assets Other Information Abstract
Estimated long-term rate of return on plan assets for 2012	8.00%
Actual rate of return on plan assets for the 15-year period	7.80%
Pension expense increase (decrease) of using differing plan asset valuation methods		$ (135)