Retirement Plans - Schedule of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Nov. 30, 2018	Nov. 30, 2017	Nov. 30, 2018	Nov. 30, 2017
Pension Plans [Member] | U.S. Pension Plans [Member]
Net Periodic Benefit Cost
Service cost	$ 172	$ 170	$ 344	$ 340
Other retirement plans (income) expense:
Interest cost	238	278	476	557
Expected return on plan assets	(376)	(406)	(753)	(812)
Amortization of prior service credit and other	(30)	(29)	(59)	(59)
Other retirement plans (income) expense	(168)	(157)	(336)	(314)
Total net periodic benefit cost	4	13	8	26
Pension Plans [Member] | International Pension Plans [Member]
Net Periodic Benefit Cost
Service cost	25	23	49	46
Other retirement plans (income) expense:
Interest cost	12	13	25	25
Expected return on plan assets	(12)	(11)	(24)	(22)
Amortization of prior service credit and other		(1)	(1)	(1)
Other retirement plans (income) expense		1		2
Total net periodic benefit cost	25	24	49	48
Postretirement Healthcare Plans [Member]
Net Periodic Benefit Cost
Service cost	8	9	17	18
Other retirement plans (income) expense:
Interest cost	10	9	20	19
Other retirement plans (income) expense	10	9	20	19
Total net periodic benefit cost	$ 18	$ 18	$ 37	$ 37