Leases (Details 1) - USD ($) $ in Millions		12 Months Ended
		May. 31, 2015	May. 31, 2014	May. 31, 2013
Operating Leases Rent Expense [Abstract]
Minimum rentals		$ 2,249	$ 2,154	$ 2,061
Contingent rentals	[1]	194	197	192
Operating leases rent expense, total		$ 2,443	$ 2,351	$ 2,253

[1] Contingent rentals are based on equipment usage.