Retirement Plans (Details 7) - USD ($) $ in Millions	12 Months Ended
	May 31, 2016	May 31, 2015	May 31, 2014
Change in Plan Assets
Company Contributions	$ 660	$ 660
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated Benefit Obligation ("ABO")	28,845	26,793
Changes in Projected Benefit Obligation ("PBO") and Accumulated Postretirement Benefit Obligation ("APBO")
PBO/APBO at the beginning of year	27,512	24,578
Service cost	662	653	$ 657
Interest cost	1,180	1,096	1,055
Actuarial loss	277	2,231
Benefits paid	(912)	(815)
Business acquisition	907
Other	(24)	(231)
PBO/APBO at the end of year	29,602	27,512	24,578
Change in Plan Assets
Beginning balance May 31	23,505	21,907
Actual return on plan assets	223	1,718
Company Contributions	726	746
Benefits paid	(912)	(815)
Business acquisition	761
Other	(32)	(51)
Ending balance May 31	24,271	23,505	21,907
Funded Status of the Plans	(5,331)	(4,007)
Amount Recognized in the Balance Sheet at May 31
Noncurrent asset	53	26
Current pension, postretirement healthcare and other benefit obligations	(31)	(34)
Noncurrent pension, postretirement healthcare and other benefit obligations	(5,353)	(3,999)
Net amount recognized	(5,331)	(4,007)
Amounts Recognized in AOCI and not yet reflected in Net Periodic Benefit Cost
Prior service (credit) cost and other	(546)	(668)
Defined Benefit Plan Amounts That Will Be Amortized From Accumulated Other Comprehensive Income Loss In Next Fiscal Year Abstract
Prior service credit and other	(121)	(121)
Postretirement Healthcare Plans [Member]
Changes in Projected Benefit Obligation ("PBO") and Accumulated Postretirement Benefit Obligation ("APBO")
PBO/APBO at the beginning of year	929	883
Service cost	40	40	38
Interest cost	42	41	40
Actuarial loss	(64)	6
Benefits paid	(78)	(73)
Other	36	32
PBO/APBO at the end of year	905	929	$ 883
Change in Plan Assets
Company Contributions	42	37
Benefits paid	(78)	(73)
Other	36	36
Funded Status of the Plans	(905)	(929)
Amount Recognized in the Balance Sheet at May 31
Current pension, postretirement healthcare and other benefit obligations	(40)	(42)
Noncurrent pension, postretirement healthcare and other benefit obligations	(865)	(887)
Net amount recognized	$ (905)	$ (929)