Short-Term Borrowings - Schedule of Short-term Debt (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Aug. 31, 2026	May 31, 2026
Short-term Debt [Line Items]
Short-term borrowings	$ 4,789,088	$ 5,159,771
Total commercial paper
Short-term Debt [Line Items]
Short-term borrowings	$ 2,666,683	$ 3,221,103
Total commercial paper \| Debt \| Credit Availability Concentration Risk
Short-term Debt [Line Items]
Concentration risk, percentage	7.00%	9.00%
Commercial paper sold through dealers, net of discounts
Short-term Debt [Line Items]
Short-term borrowings	$ 1,695,026	$ 2,338,411
Commercial paper sold through dealers, net of discounts \| Debt \| Credit Availability Concentration Risk
Short-term Debt [Line Items]
Concentration risk, percentage	5.00%	7.00%
Commercial paper sold directly to members, at par
Short-term Debt [Line Items]
Short-term borrowings	$ 971,657	$ 882,692
Commercial paper sold directly to members, at par \| Debt \| Credit Availability Concentration Risk
Short-term Debt [Line Items]
Concentration risk, percentage	2.00%	2.00%
Select notes to members
Short-term Debt [Line Items]
Short-term borrowings	$ 1,474,693	$ 1,361,207
Select notes to members \| Debt \| Credit Availability Concentration Risk
Short-term Debt [Line Items]
Concentration risk, percentage	4.00%	4.00%
Daily liquidity fund notes to members
Short-term Debt [Line Items]
Short-term borrowings	$ 353,594	$ 253,271
Daily liquidity fund notes to members \| Debt \| Credit Availability Concentration Risk
Short-term Debt [Line Items]
Concentration risk, percentage	1.00%	0.00%
Medium-term notes sold to members
Short-term Debt [Line Items]
Short-term borrowings	$ 294,118	$ 324,190
Medium-term notes sold to members \| Debt \| Credit Availability Concentration Risk
Short-term Debt [Line Items]
Concentration risk, percentage	1.00%	1.00%
Short-Term Debt \| Debt \| Credit Availability Concentration Risk
Short-term Debt [Line Items]
Concentration risk, percentage	13.00%	14.00%