Retirement Plans - Schedule of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2017	May 31, 2016	May 31, 2015
U.S. Pension Plans [Member]
Net Periodic Benefit Cost
Service cost	$ 638	$ 622	$ 615
Interest cost	1,128	1,155	1,068
Expected return on plan assets	(1,501)	(1,490)	(1,655)
Amortization of prior service credit	(118)	(118)	(112)
Actuarial losses (gains) and other	(95)	1,563	2,154
Net periodic benefit cost	52	1,732	2,070
International Pension Plans [Member]
Net Periodic Benefit Cost
Service cost	83	40	38
Interest cost	43	25	28
Expected return on plan assets	(38)	(18)	(23)
Amortization of prior service credit	(2)	(3)	(3)
Actuarial losses (gains) and other	87	(1)	36
Net periodic benefit cost	173	43	76
Postretirement Healthcare Plans [Member]
Net Periodic Benefit Cost
Service cost	36	40	40
Interest cost	39	42	41
Actuarial losses (gains) and other	(14)	(64)	6
Net periodic benefit cost	$ 61	$ 18	$ 87