Guarantees - Guarantees Outstanding (Details) - USD ($) $ in Thousands	Nov. 30, 2021	May 31, 2021
Guarantees
Guarantor obligations	$ 657,981	$ 689,080
Parent Company
Guarantees
Guarantor obligations	634,932	672,530
Parent Company | Distribution
Guarantees
Guarantor obligations	271,941	251,023
Parent Company | Power supply
Guarantees
Guarantor obligations	354,180	415,984
Parent Company | Statewide and associate
Guarantees
Guarantor obligations	8,811	5,523
NCSC
Guarantees
Guarantor obligations	23,049	16,550
Variable interest entity, primary beneficiary
Guarantees
Guarantor obligations	23,049	16,550
Variable interest entity, primary beneficiary | Statewide and associate
Guarantees
Guarantor obligations	6,000	3,000
Long-term tax-exempt bonds
Guarantees
Guarantor obligations	123,775	145,025
Letters of credit
Guarantees
Guarantor obligations	377,738	389,735
Other guarantees
Guarantees
Guarantor obligations	$ 156,468	$ 154,320