Retirement Plans - Schedule of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Feb. 29, 2020	Feb. 28, 2019	Feb. 29, 2020	Feb. 28, 2019
Pension Plans [Member] | U.S. Plans [Member]
Net Periodic Benefit Cost
Service cost	$ 192	$ 173	$ 576	$ 517
Other retirement plans (income) expense:
Interest cost	250	237	750	713
Expected return on plan assets	(400)	(376)	(1,201)	(1,129)
Amortization of prior service credit and other	(26)	(30)	(78)	(89)
Other retirement plans (income) expense	(176)	(169)	(529)	(505)
Net periodic benefit cost	16	4	47	12
Pension Plans [Member] | International Pension Plans [Member]
Net Periodic Benefit Cost
Service cost	25	23	73	72
Other retirement plans (income) expense:
Interest cost	11	13	33	38
Expected return on plan assets	(13)	(12)	(39)	(36)
Amortization of prior service credit and other	(1)		(2)	(1)
Other retirement plans (income) expense	(3)	1	(8)	1
Net periodic benefit cost	22	24	65	73
Postretirement Healthcare Plans [Member]
Net Periodic Benefit Cost
Service cost	10	9	31	26
Other retirement plans (income) expense:
Interest cost	11	10	33	30
Other retirement plans (income) expense	11	10	33	30
Net periodic benefit cost	$ 21	$ 19	$ 64	$ 56