Retirement Plans - Schedule of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2019	May 31, 2018	May 31, 2017
Pension Plans [Member] | U.S. Plans [Member]
Net Periodic Benefit Cost
Service cost	$ 689	$ 679	$ 638
Interest cost	951	1,115	1,128
Expected return on plan assets	(1,505)	(1,624)	(1,501)
Amortization of prior service credit	(118)	(118)	(118)
Actuarial losses (gains) and other	3,537	37	(95)
Net periodic benefit cost	3,554	89	52
Pension Plans [Member] | International Pension Plans [Member]
Net Periodic Benefit Cost
Service cost	94	97	83
Interest cost	49	49	43
Expected return on plan assets	(47)	(46)	(38)
Amortization of prior service credit	(2)	(2)	(2)
Actuarial losses (gains) and other	80	(38)	87
Net periodic benefit cost	174	60	173
Postretirement Healthcare Plans [Member]
Net Periodic Benefit Cost
Service cost	35	36	36
Interest cost	40	39	39
Amortization of prior service credit		(1)
Actuarial losses (gains) and other	265	(9)	(14)
Net periodic benefit cost	$ 340	$ 65	$ 61