Retirement Plans (Details 5) - USD ($) $ in Millions	12 Months Ended
	May. 31, 2015	May. 31, 2014
Defined Benefit Plan Change In Fair Value Of Plan Assets Roll Forward
Beginning balance May 31	$ 21,444
Actual return on plan assets
Ending balance May 31	23,006	$ 21,444
Fair Value Inputs Level 3 [Member]
Defined Benefit Plan Change In Fair Value Of Plan Assets Roll Forward
Beginning balance May 31	276	332
Actual return on plan assets
Assets held during current year	(15)	(17)
Assets sold during the year	43	53
Purchases, sales and settlements	(78)	(92)
Ending balance May 31	$ 226	$ 276