Retirement Plans (Details 11) (USD $) In Millions, unless otherwise specified	12 Months Ended
	May 31, 2013	May 31, 2012	May 31, 2011
Defined Benefit Plan Amounts Recognized In Other Comprehensive Income [Abstract]
Total recognized in OCI, Net of Tax Amount	$ (1,092)	$ 2,308	$ 235
Pension Plans [Member]
Defined Benefit Plan Amounts Recognized In Other Comprehensive Income [Abstract]
Net (gain) loss and other arising during period, Gross Amount	(1,350)	3,777
Amortization of prior services credit, Gross Amount	114	113
Amortization of actuarial (losses) gains and other, Gross Amount	(516)	(311)
Total recognized in OCI, Gross Amount	(1,752)	3,579
Net (gain) loss and other arising during period, Net of Tax Amount	(840)	2,371
Amortization of prior services credit, Net of Tax Amount	66	71
Amortization of actuarial (losses) gains and other, Net of Tax Amount	(297)	(195)
Total recognized in OCI, Net of Tax Amount	(1,071)	2,247
Postretirement Healthcare Plans [Member]
Defined Benefit Plan Amounts Recognized In Other Comprehensive Income [Abstract]
Net (gain) loss and other arising during period, Gross Amount	(17)	97
Amortization of actuarial (losses) gains and other, Gross Amount		1
Total recognized in OCI, Gross Amount	(17)	98
Net (gain) loss and other arising during period, Net of Tax Amount	(21)	61
Total recognized in OCI, Net of Tax Amount	$ (21)	$ 61