Income Taxes (Details 4) (USD $) In Millions, unless otherwise specified	May 31, 2013	May 31, 2012
Components Of Deferred Tax Assets [Abstract]
Property, equipment, leases and intangibles	$ 157	$ 248
Employee benefits	1,771	2,300
Self-insurance accruals	533	495
Other	251	338
Net operating loss/credit carryforwards	298	179
Valuation allowances	(204)	(145)
Deferred Tax Assets, Net	2,806	3,415
Components Of Deferred Tax Liabilities [Abstract]
Property, equipment, leases and intangibles	3,676	3,436
Employee benefits	11	11
Other	238	271
Deferred Tax Liabilities	$ 3,925	$ 3,718