Allowance for Credit Losses - Schedule of Allowance for Credit Losses on Financing Receivables (Details) - USD ($) $ in Thousands	3 Months Ended
	Aug. 31, 2026	Aug. 31, 2025
Allowance for Loan and Lease Losses [Roll Forward]
Balance at the beginning of the period	$ 29,947	$ 40,615
Provision (benefit) for credit losses	3,875	1,587
Balance at the end of the period	33,822	42,202
CFC:
Allowance for Loan and Lease Losses [Roll Forward]
Balance at the beginning of the period	24,256	35,029
Provision (benefit) for credit losses	1,633	1,085
Balance at the end of the period	25,889	36,114
CFC: \| Distribution
Allowance for Loan and Lease Losses [Roll Forward]
Balance at the beginning of the period	16,625	18,473
Provision (benefit) for credit losses	312	1,002
Balance at the end of the period	16,937	19,475
CFC: \| Power supply
Allowance for Loan and Lease Losses [Roll Forward]
Balance at the beginning of the period	6,661	15,456
Provision (benefit) for credit losses	1,306	95
Balance at the end of the period	7,967	15,551
CFC: \| Statewide and associate
Allowance for Loan and Lease Losses [Roll Forward]
Balance at the beginning of the period	970	1,100
Provision (benefit) for credit losses	15	(12)
Balance at the end of the period	985	1,088
NCSC:
Allowance for Loan and Lease Losses [Roll Forward]
Balance at the beginning of the period	5,691	5,586
Provision (benefit) for credit losses	2,242	502
Balance at the end of the period	7,933	6,088
NCSC: \| Electric
Allowance for Loan and Lease Losses [Roll Forward]
Balance at the beginning of the period	4,108	3,818
Provision (benefit) for credit losses	1,728	472
Balance at the end of the period	5,836	4,290
NCSC: \| Telecom
Allowance for Loan and Lease Losses [Roll Forward]
Balance at the beginning of the period	1,583	1,768
Provision (benefit) for credit losses	514	30
Balance at the end of the period	$ 2,097	$ 1,798