Retirement Plans (Details 10) (USD $) In Millions, unless otherwise specified	12 Months Ended
	May 31, 2013	May 31, 2012	May 31, 2011
Pension Plans [Member]
Net Periodic Benefit Cost
Service cost	$ 692	$ 593	$ 521
Interest cost	968	976	900
Expected return on plan assets	(1,383)	(1,240)	(1,062)
Recognized actuarial losses (gains) and other	402	195	184
Total net periodic benefit cost	679	524	543
Postretirement Healthcare Plans [Member]
Net Periodic Benefit Cost
Service cost	42	35	31
Interest cost	36	36	34
Recognized actuarial losses (gains) and other		(1)	(5)
Total net periodic benefit cost	$ 78	$ 70	$ 60