Retirement Plans - Schedule of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Feb. 28, 2019	Feb. 28, 2018	Feb. 28, 2019	Feb. 28, 2018
Pension Plans [Member] | U.S. Pension Plans [Member]
Net Periodic Benefit Cost
Service cost	$ 173	$ 169	$ 517	$ 509
Other retirement plans (income) expense:
Interest cost	237	279	713	836
Expected return on plan assets	(376)	(406)	(1,129)	(1,218)
Amortization of prior service credit and other	(30)	(29)	(89)	(88)
Other retirement plans (income) expense	(169)	(156)	(505)	(470)
Total net periodic benefit cost	4	13	12	39
Pension Plans [Member] | International Pension Plans [Member]
Net Periodic Benefit Cost
Service cost	23	23	72	69
Other retirement plans (income) expense:
Interest cost	13	12	38	37
Expected return on plan assets	(12)	(10)	(36)	(32)
Amortization of prior service credit and other		1	(1)
Other retirement plans (income) expense	1	3	1	5
Total net periodic benefit cost	24	26	73	74
Postretirement Healthcare Plans [Member]
Net Periodic Benefit Cost
Service cost	9	9	26	27
Other retirement plans (income) expense:
Interest cost	10	10	30	29
Other retirement plans (income) expense	10	10	30	29
Total net periodic benefit cost	$ 19	$ 19	$ 56	$ 56