Short-Term Borrowings - Outstanding (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Feb. 28, 2022	May 31, 2021
Short-term Debt [Line Items]
Short-term borrowings	$ 4,428,057	$ 4,582,096
Commercial paper
Short-term Debt [Line Items]
Short-term borrowings	$ 2,259,593	$ 2,019,584
Commercial paper | Debt | Credit availability concentration risk
Short-term Debt [Line Items]
Concentration risk, percentage	8.00%	7.00%
Commercial paper dealers, net of discounts
Short-term Debt [Line Items]
Short-term borrowings	$ 1,105,200	$ 894,977
Commercial paper dealers, net of discounts | Debt | Credit availability concentration risk
Short-term Debt [Line Items]
Concentration risk, percentage	4.00%	3.00%
Commercial paper members, at par
Short-term Debt [Line Items]
Short-term borrowings	$ 1,154,393	$ 1,124,607
Commercial paper members, at par | Debt | Credit availability concentration risk
Short-term Debt [Line Items]
Concentration risk, percentage	4.00%	4.00%
Select notes to members
Short-term Debt [Line Items]
Short-term borrowings	$ 1,402,238	$ 1,539,150
Select notes to members | Debt | Credit availability concentration risk
Short-term Debt [Line Items]
Concentration risk, percentage	5.00%	6.00%
Daily liquidity fund notes to members
Short-term Debt [Line Items]
Short-term borrowings	$ 350,402	$ 460,556
Daily liquidity fund notes to members | Debt | Credit availability concentration risk
Short-term Debt [Line Items]
Concentration risk, percentage	1.00%	2.00%
Medium-term notes to members
Short-term Debt [Line Items]
Short-term borrowings	$ 415,824	$ 362,691
Medium-term notes to members | Debt | Credit availability concentration risk
Short-term Debt [Line Items]
Concentration risk, percentage	2.00%	1.00%
Securities sold under agreements to repurchase
Short-term Debt [Line Items]
Short-term borrowings	$ 0	$ 200,115
Securities sold under agreements to repurchase | Debt | Credit availability concentration risk
Short-term Debt [Line Items]
Concentration risk, percentage	0.00%	1.00%
Short-term debt | Debt | Credit availability concentration risk
Short-term Debt [Line Items]
Concentration risk, percentage	16.00%	17.00%