Guarantees - Narrative (Details) - USD ($)	May 31, 2026	May 31, 2025	May 31, 2024
Guarantor Obligations [Line Items]
CFC third-party guarantees	$ 1,265,694,000	$ 1,210,606,000
Guarantee obligations unsecured	$ 910,000,000	$ 781,000,000
Guarantee obligations unsecured commitment as percentage of total commitment	72.00%	65.00%
Guarantee liability recorded	$ 17,000,000	$ 14,000,000
Guaranty liabilities	16,000,000	13,000,000
Letters of credit
Guarantor Obligations [Line Items]
CFC third-party guarantees	1,033,710,000	978,492,000
Guarantee obligations secured	284,000,000	356,000,000
Performance guarantee | Master letter of credit
Guarantor Obligations [Line Items]
Maximum additional amount potentially required to be issued	105,000,000
Other guarantees
Guarantor Obligations [Line Items]
CFC third-party guarantees	184,884,000	183,659,000
Guarantor obligations, maximum exposure, undiscounted	185,000,000	184,000,000
Guarantee type, other secured
Guarantor Obligations [Line Items]
Guarantor obligations, maximum exposure, undiscounted	25,000,000	25,000,000
Long-term tax-exempt bonds
Guarantor Obligations [Line Items]
CFC third-party guarantees	47,100,000	48,455,000
Financial standby letter of credit | Adjustable and floating rate tax exempt bonds
Guarantor Obligations [Line Items]
CFC third-party guarantees	$ 0	$ 0	$ 0