Retirement Plans (Details 2) - USD ($) $ in Millions	3 Months Ended
	Aug. 31, 2015	Aug. 31, 2014
Pension Plans
Net Periodic Benefit Cost
Service cost	$ 166	$ 164
Interest cost	295	275
Expected return on plan assets	(377)	(420)
Amortization of prior service credits	(31)	(26)
Total net periodic benefit cost	53	(7)
Postretirement Healthcare Plans
Net Periodic Benefit Cost
Service cost	10	10
Interest cost	11	10
Total net periodic benefit cost	$ 21	$ 20