Members' Subordinated Certificates - Schedule of subordinated borrowing (Details) - USD ($) $ in Thousands	May 31, 2022	May 31, 2021
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 986,518	$ 986,315
Weighted- Average Interest Rate	2.68%	2.66%
Subordinated certificates
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 1,234,161	$ 1,254,660
Weighted- Average Interest Rate	4.35%	4.32%
Certificates maturing 2025 through 2119
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 628,591	$ 628,582
Subscribed and unissued
Subordinated Deferrable Debt
Subordinated deferrable debt	12	12
Total membership subordinated certificates
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 628,603	$ 628,594
Weighted- Average Interest Rate	4.95%	4.95%
Interest-bearing loan subordinated certificates maturing through 2045
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 216,266	$ 223,067
Non-interest-bearing loan subordinated certificates maturing through 2047
Subordinated Deferrable Debt
Subordinated deferrable debt	121,744	132,203
Subscribed and unissued
Subordinated Deferrable Debt
Subordinated deferrable debt	45	45
Loan subordinated certificates
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 338,055	$ 355,315
Weighted- Average Interest Rate	2.64%	2.61%
Interest-bearing guarantee subordinated certificates maturing through 2044
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 27,333	$ 31,581
Weighted- Average Interest Rate	5.90%	6.06%
Loan and guarantee subordinated certificates
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 365,388	$ 386,896
Weighted- Average Interest Rate	2.88%	2.89%
Securities maturing through 2052
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 240,170	$ 239,170
Weighted- Average Interest Rate	5.00%	5.00%