Retirement Plans - Schedule of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Nov. 30, 2017	Nov. 30, 2016	Nov. 30, 2017	Nov. 30, 2016
Pension Plans [Member] | U.S. Pension Plans [Member]
Net Periodic Benefit Cost
Service cost	$ 170	$ 160	$ 340	$ 319
Interest cost	278	282	557	564
Expected return on plan assets	(406)	(375)	(812)	(751)
Amortization of prior service credit and other	(29)	(30)	(59)	(59)
Total net periodic benefit cost	13	37	26	73
Pension Plans [Member] | International Pension Plans [Member]
Net Periodic Benefit Cost
Service cost	23	20	46	41
Interest cost	13	11	25	22
Expected return on plan assets	(11)	(11)	(22)	(21)
Amortization of prior service credit and other	(1)	1	(1)	1
Total net periodic benefit cost	24	21	48	43
Postretirement Healthcare Plans [Member]
Net Periodic Benefit Cost
Service cost	9	9	18	18
Interest cost	9	10	19	20
Total net periodic benefit cost	$ 18	$ 19	$ 37	$ 38