Retirement Plans - Schedule of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Nov. 30, 2019	Nov. 30, 2018	Nov. 30, 2019	Nov. 30, 2018
Pension Plans [Member] | U.S. Plans [Member]
Net Periodic Benefit Cost
Service cost	$ 192	$ 172	$ 384	$ 344
Other retirement plans (income) expense:
Interest cost	250	238	500	476
Expected return on plan assets	(401)	(376)	(801)	(753)
Amortization of prior service credit and other	(25)	(30)	(52)	(59)
Other retirement plans (income) expense	(176)	(168)	(353)	(336)
Net periodic benefit cost	16	4	31	8
Pension Plans [Member] | International Pension Plans [Member]
Net Periodic Benefit Cost
Service cost	24	25	48	49
Other retirement plans (income) expense:
Interest cost	11	12	22	25
Expected return on plan assets	(13)	(12)	(26)	(24)
Amortization of prior service credit and other	(1)		(1)	(1)
Other retirement plans (income) expense	(3)		(5)
Net periodic benefit cost	21	25	43	49
Postretirement Healthcare Plans [Member]
Net Periodic Benefit Cost
Service cost	10	8	21	17
Other retirement plans (income) expense:
Interest cost	11	10	22	20
Other retirement plans (income) expense	11	10	22	20
Net periodic benefit cost	$ 21	$ 18	$ 43	$ 37