Retirement Plans - Schedule of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2020	May 31, 2019	May 31, 2018
U.S. Plans [Member]
Net Periodic Benefit Cost
Service cost	$ 768
Interest cost	1,000
Expected return on plan assets	(1,601)
Amortization of prior service credit	(105)
Actuarial losses (gains) and other	888
Net periodic benefit cost	950
Pension Plans [Member] | U.S. Plans [Member]
Net Periodic Benefit Cost
Service cost	768	$ 689	$ 679
Interest cost	1,000	951	1,115
Expected return on plan assets		(1,505)	(1,624)
Amortization of prior service credit		(118)	(118)
Actuarial losses (gains) and other		3,537	37
Net periodic benefit cost		3,554	89
Pension Plans [Member] | International Pension Plans [Member]
Net Periodic Benefit Cost
Service cost	96	94	97
Interest cost	43	49	49
Expected return on plan assets	(52)	(47)	(46)
Amortization of prior service credit	(2)	(2)	(2)
Actuarial losses (gains) and other	(179)	80	(38)
Net periodic benefit cost	(94)	174	60
Postretirement Healthcare Plans [Member]
Net Periodic Benefit Cost
Service cost	42	35	36
Interest cost	44	40	39
Amortization of prior service credit			(1)
Actuarial losses (gains) and other	85	265	(9)
Net periodic benefit cost	$ 171	$ 340	$ 65