Guarantees - Additional Information (Details) - USD ($)	Aug. 31, 2026	May 31, 2026
Guarantees
Guarantor obligations	$ 1,248,566,000	$ 1,265,694,000
Guarantee obligations unsecured	$ 902,000,000	$ 910,000,000
Guarantee obligations unsecured commitment as percentage of total commitment	72.00%	72.00%
Guarantee liability recorded	$ 16,000,000	$ 17,000,000
Guaranty liabilities	15,000,000	16,000,000
Long-term tax-exempt bonds
Guarantees
Guarantor obligations	45,215,000	47,100,000
Letters of credit
Guarantees
Guarantor obligations	1,019,319,000	1,033,710,000
Guarantee obligations secured	277,000,000	284,000,000
Performance guarantee \| Master Letter Of Credit
Guarantees
Maximum additional amount potentially required to be issued	101,000,000
Other guarantees
Guarantees
Guarantor obligations	184,032,000	184,884,000
Guarantor obligations, maximum exposure, undiscounted	184,000,000	185,000,000
Other secured guarantees
Guarantees
Guarantor obligations, maximum exposure, undiscounted	25,000,000	25,000,000
Financial standby letter of credit \| Adjustable And Floating Rate Tax Exempt Bonds
Guarantees
Guarantor obligations	$ 0	$ 0

Guarantee Liability Recorded

No definition available.

Name:	nruc_GuaranteeLiabilityRecorded
Namespace Prefix:	nruc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the amount of guarantee obligations secured.

+ References

No definition available.

+ Details

Name:	nruc_GuaranteeObligationsSecured
Namespace Prefix:	nruc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the amount of guarantee obligations with unsecured rights of recovery from the entity's members.

+ References

No definition available.

+ Details

Name:	nruc_GuaranteeObligationsUnsecured
Namespace Prefix:	nruc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the unsecured guarantee obligations as a percentage of total guarantee obligations.

+ References

No definition available.

+ Details

Name:	nruc_GuaranteeObligationsUnsecuredCommitmentAsPercentageOfTotalCommitment
Namespace Prefix:	nruc_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the maximum potential additional amount that may be required to be issued to third parties for the benefit of the entity's members.

+ References

No definition available.

+ Details

Name:	nruc_LetterOfCreditFacilityMaximumAdditionalAmountPotentiallyRequiredToBeIssued
Namespace Prefix:	nruc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-4

+ Details

Name:	us-gaap_GuaranteeObligationsCurrentCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-4

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-4

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-4

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-4

+ Details

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

- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-4

+ Details

Name:	us-gaap_GuaranteeObligationsMaximumExposure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This item represents a non-contingent liability for the fair value of an obligation to stand ready to perform over the term of a guaranty issued in the event that specified triggering events or conditions occur.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 25
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482050/460-10-25-4

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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- Details

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- Details

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Namespace Prefix:
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- Details

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- Details

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- Details

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- Details

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Namespace Prefix:
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- Details

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