Summary of Quarterly Operating Results (Unaudited) (Details) (USD $) In Millions, except Per Share data	3 Months Ended																12 Months Ended
	May 31, 2011		Feb. 28, 2011		Nov. 30, 2010		Aug. 31, 2010		May 31, 2010		Feb. 28, 2010		Nov. 30, 2009		Aug. 31, 2009		May 31, 2011	May 31, 2010	May 31, 2009
Selected Quarterly Financial Information Abstract
Revenues	$ 10,552		$ 9,663		$ 9,632		$ 9,457		$ 9,428		$ 8,701		$ 8,596		$ 8,009		$ 39,304	$ 34,734	$ 35,497
Operating Income	888		393		469		628		696		416		571		315		2,378	1,998	747
Net income	$ 558		$ 231		$ 283		$ 380		$ 419		$ 239		$ 345		$ 181		$ 1,452	$ 1,184	$ 98
Basic earnings per common share	$ 1.76	[1]	$ 0.73	[1]	$ 0.90	[1]	$ 1.21	[1]	$ 1.34		$ 0.76		$ 1.10		$ 0.58		$ 4.61	$ 3.78	$ 0.31
Diluted earnings per common share	$ 1.75		$ 0.73		$ 0.89		$ 1.20		$ 1.33	[1]	$ 0.76	[1]	$ 1.10	[1]	$ 0.58	[1]	$ 4.57	$ 3.76	$ 0.31

[1] The sum of the quarterly earnings per share may not equal annual amounts due to differences in the weighted-average number of shares outstanding during the respective period.