Leases - Schedule of Rent Expense Under Operating Leases (Details) - USD ($) $ in Millions		12 Months Ended
		May 31, 2017	May 31, 2016	May 31, 2015
Operating Leases Rent Expense [Abstract]
Minimum rentals		$ 2,814	$ 2,394	$ 2,249
Contingent rentals	[1]	178	214	194
Operating leases rent expense, total		$ 2,992	$ 2,608	$ 2,443

[1] Contingent rentals are based on equipment usage.