Guarantees - Summary of total guarantees by type of guarantee and member class (Details) - USD ($) $ in Thousands	May 31, 2026	May 31, 2025
Guarantor Obligations [Line Items]
Guarantor obligations	$ 1,265,694	$ 1,210,606
CFC
Guarantor Obligations [Line Items]
Guarantor obligations	1,167,682	1,150,042
CFC | Distribution
Guarantor Obligations [Line Items]
Guarantor obligations	508,383	506,834
CFC | Power supply
Guarantor Obligations [Line Items]
Guarantor obligations	614,234	599,766
CFC | Statewide and associate
Guarantor Obligations [Line Items]
Guarantor obligations	45,065	43,442
NCSC
Guarantor Obligations [Line Items]
Guarantor obligations	98,012	60,564
Variable interest entity, primary beneficiary
Guarantor Obligations [Line Items]
Guarantor obligations	105,346	60,564
Variable interest entity, primary beneficiary | Statewide and associate
Guarantor Obligations [Line Items]
Guarantor obligations	37,000	42,000
Long-term tax-exempt bonds
Guarantor Obligations [Line Items]
Guarantor obligations	47,100	48,455
Letters of credit
Guarantor Obligations [Line Items]
Guarantor obligations	1,033,710	978,492
Other guarantees
Guarantor Obligations [Line Items]
Guarantor obligations	$ 184,884	$ 183,659