Retirement Plans - Schedule of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Aug. 31, 2017	Aug. 31, 2016
U.S. Pension Plans [Member]
Net Periodic Benefit Cost
Service cost	$ 170	$ 160
Interest cost	279	282
Expected return on plan assets	(406)	(375)
Amortization of prior service credit and other	(30)	(30)
Total net periodic benefit cost	13	37
International Pension Plans [Member]
Net Periodic Benefit Cost
Service cost	23	20
Interest cost	12	11
Expected return on plan assets	(11)	(11)
Amortization of prior service credit and other		1
Total net periodic benefit cost	24	21
Postretirement Healthcare Plans [Member]
Net Periodic Benefit Cost
Service cost	9	9
Interest cost	10	10
Total net periodic benefit cost	$ 19	$ 19