Short-Term Borrowings - Schedule of Short-term Debt (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Feb. 28, 2026	May 31, 2025
Short-term Debt [Line Items]
Short-term borrowings	$ 5,100,828	$ 5,091,416
Total commercial paper
Short-term Debt [Line Items]
Short-term borrowings	$ 3,138,121	$ 2,992,059
Total commercial paper | Debt | Credit Availability Concentration Risk
Short-term Debt [Line Items]
Concentration risk, percentage	9.00%	9.00%
Commercial paper sold through dealers, net of discounts
Short-term Debt [Line Items]
Short-term borrowings	$ 2,192,686	$ 2,206,451
Commercial paper sold through dealers, net of discounts | Debt | Credit Availability Concentration Risk
Short-term Debt [Line Items]
Concentration risk, percentage	6.00%	7.00%
Commercial paper sold directly to members, at par
Short-term Debt [Line Items]
Short-term borrowings	$ 945,435	$ 785,608
Commercial paper sold directly to members, at par | Debt | Credit Availability Concentration Risk
Short-term Debt [Line Items]
Concentration risk, percentage	3.00%	2.00%
Select notes to members
Short-term Debt [Line Items]
Short-term borrowings	$ 1,301,078	$ 1,304,240
Select notes to members | Debt | Credit Availability Concentration Risk
Short-term Debt [Line Items]
Concentration risk, percentage	3.00%	4.00%
Daily liquidity fund notes to members
Short-term Debt [Line Items]
Short-term borrowings	$ 294,776	$ 343,916
Daily liquidity fund notes to members | Debt | Credit Availability Concentration Risk
Short-term Debt [Line Items]
Concentration risk, percentage	1.00%	1.00%
Medium-term notes sold to members
Short-term Debt [Line Items]
Short-term borrowings	$ 366,853	$ 451,201
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	14.00%	15.00%