Members' Subordinated Certificates - Schedule of subordinated borrowing (Details) - USD ($) $ in Thousands	May 31, 2026	May 31, 2025
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 1,310,282	$ 1,329,485
Weighted- Average Interest Rate	3.99%	3.99%
Subordinated certificates
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 1,128,240	$ 1,184,714
Weighted- Average Interest Rate	4.54%	4.46%
Certificates maturing 2030 through 2119
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 627,254	$ 628,617
Subscribed and unissued
Subordinated Deferrable Debt
Subordinated deferrable debt	18	20
Total membership subordinated certificates
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 627,272	$ 628,637
Weighted- Average Interest Rate	4.96%	4.96%
Interest-bearing loan subordinated certificates maturing through 2045
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 141,626	$ 192,779
Non-interest-bearing loan subordinated certificates maturing through 2047
Subordinated Deferrable Debt
Subordinated deferrable debt	85,405	90,378
Loan subordinated certificates
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 227,031	$ 283,157
Weighted- Average Interest Rate	2.69%	2.74%
Interest-bearing guarantee subordinated certificates maturing through 2044
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 26,640	$ 26,757
Weighted- Average Interest Rate	5.95%	5.93%
Loan and guarantee subordinated certificates
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 253,671	$ 309,914
Weighted- Average Interest Rate	3.03%	3.02%
Securities maturing through 2056
Subordinated Deferrable Debt
Subordinated deferrable debt	$ 247,297	$ 246,163
Weighted- Average Interest Rate	5.01%	5.01%