Members' Subordinated Certificates - Schedule of subordinated borrowing (Details) - USD ($) $ in Thousands	May 31, 2023	May 31, 2022
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 1,283,436	$ 986,518
Weighted- Average Interest Rate	3.44%	2.68%
Subordinated certificates
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 1,223,126	$ 1,234,161
Weighted- Average Interest Rate	4.38%	4.35%
Certificates maturing 2025 through 2119
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 628,595	$ 628,591
Subscribed and unissued
Subordinated Deferrable Debt
Subordinated deferrable debt	19	12
Total membership subordinated certificates
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 628,614	$ 628,603
Weighted- Average Interest Rate	4.94%	4.95%
Interest-bearing loan subordinated certificates maturing through 2045
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 208,192	$ 216,266
Non-interest-bearing loan subordinated certificates maturing through 2047
Subordinated Deferrable Debt
Subordinated deferrable debt	112,978	121,744
Subscribed and unissued
Subordinated Deferrable Debt
Subordinated deferrable debt	41	45
Loan subordinated certificates
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 321,211	$ 338,055
Weighted- Average Interest Rate	2.65%	2.64%
Interest-bearing guarantee subordinated certificates maturing through 2044
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 27,138	$ 27,333
Weighted- Average Interest Rate	5.91%	5.90%
Loan and guarantee subordinated certificates
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 348,349	$ 365,388
Weighted- Average Interest Rate	2.91%	2.88%
Securities maturing through 2052
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 246,163	$ 240,170
Weighted- Average Interest Rate	5.01%	5.00%