Loans - Schedule of loans outstanding to members and unadvanced commitments by loan type and by member class (Details) - USD ($) $ in Thousands	May 31, 2026	May 31, 2025
Unadvanced Loan Commitments
Total loans outstanding	$ 38,403,415	$ 37,063,548
Deferred loan origination costs	18,713	16,430
Loans to members	$ 38,422,128	$ 37,079,978
Financing Receivable, before Allowance for Credit Loss, to Total, Percent	100.00%	100.00%
Long-term loans
Unadvanced Loan Commitments
Total loans outstanding	$ 33,820,842	$ 32,510,563
Financing Receivable, before Allowance for Credit Loss, to Total, Percent	88.00%	88.00%
Fixed rate
Unadvanced Loan Commitments
Total loans outstanding	$ 32,384,884	$ 31,388,313
Financing Receivable, before Allowance for Credit Loss, to Total, Percent	84.00%	85.00%
Variable rate
Unadvanced Loan Commitments
Total loans outstanding	$ 1,435,958	$ 1,122,250
Financing Receivable, before Allowance for Credit Loss, to Total, Percent	4.00%	3.00%
Lines of credit
Unadvanced Loan Commitments
Total loans outstanding	$ 4,582,573	$ 4,552,985
Financing Receivable, before Allowance for Credit Loss, to Total, Percent	12.00%	12.00%
Unamortized loan commitment and origination fees
Unadvanced Loan Commitments
Deferred loan origination costs	$ 18,713	$ 16,430
Financing Receivable, before Allowance for Credit Loss, to Total, Percent	0.00%	0.00%
CFC
Unadvanced Loan Commitments
Total loans outstanding	$ 36,747,017	$ 35,409,320
Deferred loan origination costs	$ 19,000	$ 16,000
Financing Receivable, before Allowance for Credit Loss, to Total, Percent	95.00%	95.00%
CFC \| Distribution
Unadvanced Loan Commitments
Total loans outstanding	$ 30,085,224	$ 29,262,495
Financing Receivable, before Allowance for Credit Loss, to Total, Percent	78.00%	79.00%
CFC \| Power supply
Unadvanced Loan Commitments
Total loans outstanding	$ 6,403,396	$ 5,895,500
Financing Receivable, before Allowance for Credit Loss, to Total, Percent	17.00%	16.00%
CFC \| Statewide and associate
Unadvanced Loan Commitments
Total loans outstanding	$ 258,397	$ 251,325
Financing Receivable, before Allowance for Credit Loss, to Total, Percent	0.00%	0.00%
NCSC
Unadvanced Loan Commitments
Total loans outstanding	$ 1,656,398	$ 1,654,228
Financing Receivable, before Allowance for Credit Loss, to Total, Percent	5.00%	5.00%
NCSC \| Electric
Unadvanced Loan Commitments
Total loans outstanding	$ 1,073,794	$ 1,078,763
Financing Receivable, before Allowance for Credit Loss, to Total, Percent	3.00%	3.00%
NCSC \| Telecom
Unadvanced Loan Commitments
Total loans outstanding	$ 582,604	$ 575,465
Financing Receivable, before Allowance for Credit Loss, to Total, Percent	2.00%	2.00%

Percentage, before allowance for credit loss, of financing receivable to total financing receivable.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph c
-Publisher SEC

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Amortized cost excluding accrued interest, before allowance for credit loss, of financing receivable. Excludes net investment in lease.

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Amortized cost excluding accrued interest, before allowance for credit loss, fee, and loan in process, of financing receivable. Excludes net investment in lease.

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Amount of unamortized loan commitment, origination, and other costs (fees) on financing receivable recognized as adjustment to yield. Excludes financing receivable covered under loss sharing agreement.

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