Loans - Outstanding Principal Balance and Unadvanced Commitments (Details) - USD ($) $ in Thousands	Aug. 31, 2023	May 31, 2023	Aug. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 33,083,493	$ 32,519,349	$ 30,674,996
Deferred loan origination costs	13,153		12,335
Loans to members	$ 33,096,646	$ 32,532,086	$ 30,687,331
% of total loans outstanding	100.00%	100.00%
Long-term loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 29,721,029	$ 29,396,011
% of total loans outstanding	90.00%	90.00%
Fixed rate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 28,708,848	$ 28,371,358
% of total loans outstanding	87.00%	87.00%
Variable rate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 1,012,181	$ 1,024,653
% of total loans outstanding	3.00%	3.00%
Lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 3,362,464	$ 3,123,338
% of total loans outstanding	10.00%	10.00%
Deferred loan origination costs—CFC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Deferred loan origination costs	$ 13,153	$ 12,737
% of total loans outstanding	0.00%	0.00%
CFC:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 31,621,070	$ 31,074,687
Deferred loan origination costs	$ 13,000	$ 13,000
% of total loans outstanding	96.00%	96.00%
CFC: \| Distribution
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 25,818,224	$ 25,437,077
% of total loans outstanding	78.00%	78.00%
CFC: \| Power supply
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 5,570,554	$ 5,437,242
% of total loans outstanding	17.00%	17.00%
CFC: \| Statewide and associate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 232,292	$ 200,368
% of total loans outstanding	1.00%	1.00%
NCSC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 923,447	$ 956,874
% of total loans outstanding	2.00%	3.00%
RTFC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount	$ 538,976	$ 487,788
% of total loans outstanding	2.00%	1.00%

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

+ Details

Name:	srt_FinancingReceivableBeforeAllowanceForCreditLossToTotalPercent
Namespace Prefix:	srt_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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

No definition available.

+ Details

Name:	us-gaap_AccountsNotesAndLoansReceivableLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-3B

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-5

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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/2009/role/commonPracticeRef
-Topic 310
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481598/310-20-45-2

Reference 2: 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//1943274/2147479853/942-210-S99-1

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLossFeeAndLoanInProcess
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-4

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-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 3: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-SubTopic 20
-Topic 310
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481569/310-20-50-3

+ Details

Name:	us-gaap_FinancingReceivableUnamortizedLoanFeeCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=nruc_LongTermLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=nruc_LongTermFixedRateLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=nruc_LongTermVariableRateLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=nruc_LineOfCreditLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=nruc_UnamortizedLoanCommitmentAndOriginationFeesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_ParentCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivablesByIndustryOfCounterpartyTypeAxis=nruc_DistributionSystemsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivablesByIndustryOfCounterpartyTypeAxis=nruc_PowerSupplySystemsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivablesByIndustryOfCounterpartyTypeAxis=nruc_StatewideAndAssociateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=nruc_NationalCooperativeServicesCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=nruc_RuralTelephoneFinanceCooperativeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: