Guarantees - Summary of total guarantees by type of guarantee and member class (Details) - USD ($)	May 31, 2023	May 31, 2022
Guarantor Obligations [Line Items]
CFC third-party guarantees	$ 796,821,000	$ 730,783,000
Long-term tax-exempt bonds
Guarantor Obligations [Line Items]
CFC third-party guarantees	98,405,000	122,150,000
Letters of credit
Guarantor Obligations [Line Items]
CFC third-party guarantees	538,393,000	450,354,000
Other guarantees
Guarantor Obligations [Line Items]
CFC third-party guarantees	160,023,000	158,279,000
Performance guarantee | Hybrid Letter Of Credit
Guarantor Obligations [Line Items]
Letter of credit facility maximum additional amount potentially required to be issued	35,000,000
CFC
Guarantor Obligations [Line Items]
CFC third-party guarantees	781,558,000	706,813,000
CFC | Distribution
Guarantor Obligations [Line Items]
CFC third-party guarantees	383,644,000	314,925,000
CFC | Power supply
Guarantor Obligations [Line Items]
CFC third-party guarantees	380,382,000	378,516,000
CFC | Statewide and associate
Guarantor Obligations [Line Items]
CFC third-party guarantees	17,532,000	13,372,000
NCSC
Guarantor Obligations [Line Items]
CFC third-party guarantees	15,263,000	23,970,000
Variable interest entity, primary beneficiary
Guarantor Obligations [Line Items]
CFC third-party guarantees	15,263,000	23,970,000
Variable interest entity, primary beneficiary | Statewide and associate
Guarantor Obligations [Line Items]
CFC third-party guarantees	$ 16,000,000	$ 11,000,000