Retirement Plans (Details 6) - USD ($) $ in Millions	12 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2013
Change in Plan Assets
Beginning balance May 31	$ 21,444
Ending balance May 31	23,006	$ 21,444
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated Benefit Obligation ("ABO")	26,793	23,805
Changes in Projected Benefit Obligation ("PBO") and Accumulated Postretirement Benefit Obligation ("APBO")
PBO/APBO at the beginning of year	24,578	22,600
Service cost	653	657	$ 692
Interest cost	1,096	1,055	968
Actuarial loss	2,231	1,021
Benefits paid	(815)	(801)
Other	(231)	46
PBO/APBO at the end of year	27,512	24,578	22,600
Change in Plan Assets
Beginning balance May 31	21,907	19,433
Actual return on plan assets	1,718	2,509
Company contributions	746	727
Benefits paid	(815)	(801)
Other	(51)	39
Ending balance May 31	23,505	21,907	19,433
Funded Status of the Plans	(4,007)	(2,671)
Amount Recognized in the Balance Sheet at May 31
Noncurrent asset	26	5
Current pension, postretirement healthcare and other benefit obligations	(34)	(41)
Noncurrent pension, postretirement healthcare and other benefit obligations	(3,999)	(2,635)
Net amount recognized	(4,007)	(2,671)
Amounts Recognized in AOCI and not yet reflected in Net Periodic Benefit Cost
Prior service (credit) cost and other	(668)	(670)
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)	(115)
Postretirement Healthcare Plans [Member]
Changes in Projected Benefit Obligation ("PBO") and Accumulated Postretirement Benefit Obligation ("APBO")
PBO/APBO at the beginning of year	883	828
Service cost	40	38	42
Interest cost	41	40	36
Actuarial loss	6	5
Benefits paid	(73)	(62)
Other	32	34
PBO/APBO at the end of year	929	883	$ 828
Change in Plan Assets
Company contributions	37	28
Benefits paid	(73)	(62)
Other	36	34
Funded Status of the Plans	(929)	(883)
Amount Recognized in the Balance Sheet at May 31
Current pension, postretirement healthcare and other benefit obligations	(42)	(41)
Noncurrent pension, postretirement healthcare and other benefit obligations	(887)	(842)
Net amount recognized	$ (929)	(883)
Amounts Recognized in AOCI and not yet reflected in Net Periodic Benefit Cost
Prior service (credit) cost and other		$ 1