Short-Term Debt and Credit Arrangements - Short-Term Debt Table (Details) (USD $)	Aug. 31, 2014		May 31, 2014
Short-Term Debt Outstanding
Short-term debt	$ 4,173,390,000		$ 4,099,331,000
Long-term Debt, Reclassified from Short-term			1,300,000,000
Short-term debt
Short-Term Debt Outstanding
Short-term debt	4,173,390,000		4,099,331,000
Short-term debt | Select notes
Short-Term Debt Outstanding
Short-term debt	608,046,000		548,610,000
Short-term debt | Daily liquidity fund notes
Short-Term Debt Outstanding
Short-term debt	582,373,000		486,501,000
Short-term debt | Bank bid notes
Short-Term Debt Outstanding
Short-term debt	0		20,000,000
Short-term debt | Commercial paper sold through dealers, net of discounts
Short-Term Debt Outstanding
Short-term debt	1,959,894,000	[1]	1,973,557,000	[1]
Short-term debt | Commercial paper sold directly to members, at par
Short-Term Debt Outstanding
Short-term debt	794,439,000	[1]	838,074,000	[1]
Short-term debt | Commercial paper sold directly to non-members, at par
Short-Term Debt Outstanding
Short-term debt	19,793,000	[1]	20,315,000	[1]
Short-term debt | Medium Term Notes Sold to Members
Short-Term Debt Outstanding
Short-term debt	$ 208,845,000		$ 212,274,000

[1] Backup liquidity is provided by our revolving credit agreements.