Retirement Plans (Details 12) - USD ($) $ in Millions	12 Months Ended
	May 31, 2016	May 31, 2015	May 31, 2014
Pension Plans [Member]
Net Periodic Benefit Cost
Service cost	$ 662	$ 653	$ 657
Interest cost	1,180	1,096	1,055
Expected return on plan assets	(1,508)	(1,678)	(1,495)
Amortization of prior service credit	(121)	(115)	(115)
Recognized actuarial losses (gains) and other	1,562	2,190	7
Total net periodic benefit cost	1,775	2,146	109
Postretirement Healthcare Plans [Member]
Net Periodic Benefit Cost
Service cost	40	40	38
Interest cost	42	41	40
Recognized actuarial losses (gains) and other	(64)	6	5
Total net periodic benefit cost	$ 18	$ 87	$ 83