Income Taxes (Details 4) - USD ($) $ in Millions	May. 31, 2015	May. 31, 2014
Components Of Deferred Tax Assets [Abstract]
Property, equipment, leases and intangibles	$ 93	$ 120
Employee benefits	2,029	1,464
Self-insurance accruals	607	555
Other	477	368
Net operating loss/credit carryforwards	326	333
Valuation allowances	(224)	(245)
Deferred Tax Assets, Net	3,308	2,595
Components Of Deferred Tax Liabilities [Abstract]
Property, equipment, leases and intangibles	3,872	3,730
Employee benefits	13	11
Other	414	366
Deferred Tax Liabilities	$ 4,299	$ 4,107