Computation of Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended																12 Months Ended
		May. 31, 2015	[2]	Feb. 28, 2015	[2]	Nov. 30, 2014	[2]	Aug. 31, 2014	[2]	May. 31, 2014	[2]	Feb. 28, 2014	[2]	Nov. 30, 2013	[2]	Aug. 31, 2013	[2]	May. 31, 2015	May. 31, 2014	May. 31, 2013
Basic earnings per common share:
Net earnings allocable to common shares	[1]																	$ 1,048	$ 2,320	$ 2,711
Weighted-average common shares																		283.0	307.0	315.0
Basic earnings per common share		$ (3.16)		$ 2.21		$ 2.34		$ 2.29		$ 2.66		$ 1.44		$ 1.77		$ 1.73		$ 3.70	$ 7.56	$ 8.61
Diluted earnings per common share:
Net earnings allocable to common shares	[1]																	$ 1,048	$ 2,320	$ 2,711
Weighted-average common shares																		283.0	307.0	315.0
Dilutive effect of share-based awards																		4.0	3.0	2.0
Weighted-average diluted shares																		287.0	310.0	317.0
Diluted earnings per common share		$ (3.16)		$ 2.18		$ 2.31		$ 2.26		$ 2.62		$ 1.42		$ 1.75		$ 1.72		$ 3.65	$ 7.48	$ 8.55
Anti-dilutive options excluded from diluted earnings per common share																		2.1	3.3	11.1

[1] Net earnings available to participating securities were immaterial in all periods presented.

[2] 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 periods.