Loans - Nonperforming Loans (Details) $ in Thousands	3 Months Ended	9 Months Ended
	Aug. 31, 2022 borrower	Feb. 28, 2023 USD ($) borrower	May 31, 2022 USD ($)	Feb. 28, 2022 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans to members		$ 32,381,829	$ 30,063,386	$ 29,520,381
% of Total Loans Outstanding		100.00%	100.00%
Nonperforming financial instruments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Borrowers | borrower	3	2
Loans to members		$ 108,167	$ 227,790
% of Total Loans Outstanding		0.33%	0.76%
Parent Company
Accounts, Notes, Loans and Financing Receivable [Line Items]
% of Total Loans Outstanding		95.00%	96.00%
Parent Company | Power supply
Accounts, Notes, Loans and Financing Receivable [Line Items]
% of Total Loans Outstanding		16.00%	17.00%
Parent Company | Power supply | Nonperforming financial instruments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Borrowers | borrower	3	2
Loans to members		$ 108,167	$ 227,790
% of Total Loans Outstanding		0.33%	0.76%