Members' Subordinated Certificates - Narrative (Details)	12 Months Ended
	May 31, 2026	May 31, 2025	May 31, 2023
Members' subordinated certificates
Maturity period		30 years
Membership subordinated certificates
Members' subordinated certificates
Maturity period	100 years
Interest rate	5.00%
Member capital security, call option term	5 years		10 years
Securities maturing through 2056
Members' subordinated certificates
Maturity period	30 years
Weighted average | Membership subordinated certificates
Members' subordinated certificates
Maturity period	51 years	52 years