Loans - Nonperforming Loans (Details) $ in Thousands	6 Months Ended	12 Months Ended
	Nov. 30, 2021 USD ($) borrower	May 31, 2021 USD ($) borrower	Nov. 30, 2020 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding amount	$ 28,934,814	$ 28,415,107	$ 27,051,163
% of total loans outstanding	100.00%	100.00%
Nonperforming financial instruments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Borrowers | borrower	2	4
Outstanding amount	$ 219,444	$ 237,497
% of total loans outstanding	0.76%	0.84%
Parent Company
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding amount	$ 27,781,874	$ 27,287,856
% of total loans outstanding	96.00%	96.00%
Parent Company | Brazos electric power cooperative
Accounts, Notes, Loans and Financing Receivable [Line Items]
Letters of Credit Outstanding		$ 1,000
Parent Company | Power supply
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding amount	$ 5,122,406	$ 5,154,312
% of total loans outstanding	18.00%	18.00%
Parent Company | Power supply | Brazos electric power cooperative
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding amount		$ 85,000
Parent Company | Nonperforming financial instruments | Power supply
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Borrowers | borrower	2	2
Outstanding amount	$ 219,444	$ 228,312
% of total loans outstanding	0.76%	0.81%
RTFC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding amount	$ 431,641	$ 420,383
% of total loans outstanding	1.00%	1.00%
RTFC | Nonperforming financial instruments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Borrowers | borrower	0	2
Outstanding amount	$ 0	$ 9,185
% of total loans outstanding	0.00%	0.03%