Loans - Schedule of Loans Outstanding to Members and Unadvanced Commitments by Loan Type and by Member Class (Details) - USD ($) $ in Thousands	Feb. 28, 2026	May 31, 2025	Feb. 28, 2025
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 38,731,679	$ 37,063,548	$ 36,463,440
Deferred loan origination costs—CFC	18,203		15,769
Loans to members	$ 38,749,882	$ 37,079,978	$ 36,479,209
% of Total	100.00%	100.00%
Long-term loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 33,584,405	$ 32,510,563
% of Total	87.00%	88.00%
Fixed rate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 32,145,476	$ 31,388,313
% of Total	83.00%	85.00%
Variable rate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 1,438,929	$ 1,122,250
% of Total	4.00%	3.00%
Lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 5,147,274	$ 4,552,985
% of Total	13.00%	12.00%
Deferred Loan Origination Costs—CFC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Deferred loan origination costs—CFC	$ 18,203	$ 16,430
% of Total	0.00%	0.00%
CFC:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 36,949,300	$ 35,409,320
Deferred loan origination costs—CFC	$ 18,000	$ 16,000
% of Total	95.00%	95.00%
CFC: \| Distribution
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 30,387,286	$ 29,262,495
% of Total	78.00%	79.00%
CFC: \| Power supply
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 6,288,837	$ 5,895,500
% of Total	16.00%	16.00%
CFC: \| Statewide and associate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 273,177	$ 251,325
% of Total	1.00%	0.00%
NCSC:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 1,782,379	$ 1,654,228
% of Total	5.00%	5.00%
NCSC: \| Electric
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 1,163,391	$ 1,078,763
% of Total	3.00%	3.00%
NCSC: \| Telecom
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 618,988	$ 575,465
% of Total	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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 20
-Name Accounting Standards Codification
-Section 40
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481628/310-20-40-7

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-SubTopic 10
-Name Accounting Standards Codification
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-Paragraph 2
-Publisher FASB
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Amortized cost excluding accrued interest, before allowance for credit loss, of financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Publisher FASB
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-Topic 326
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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(7))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481598/310-20-45-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org/1943274/2147481962/310-10-50-4

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