Guarantees (Details Textual) (USD $)	9 Months Ended
Feb. 28, 2014	May 31, 2013
Guarantor Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	$ 1,106,211,000	$ 1,112,771,000
Guarantee Obligations Unsecured	456,000,000	410,000,000
Guarantee Obligations Unsecured Commitment as Percentage of Total Commitment	41.00%	41.00%
Value of bonds issued under liquidity provider obligations	571,000,000
Guaranty Liabilities Contingent and Noncontingent	23,172,000	24,742,000
Guaranty Liabilities Contingent	2,000,000	2,000,000
Guaranty Liabilities	21,000,000	23,000,000
Letter of Credit
Guarantor Obligations [Line Items]
Maturity Period	2024
Long-term variable-rate bonds
Guarantor Obligations [Line Items]
Value of bonds issued under liquidity provider obligations	446,000,000
Letter of Credit Secured \| Letter of Credit
Guarantor Obligations [Line Items]
Guarantee Obligations Unsecured	131,000,000
Master Letter of Credit \| Letter of Credit
Guarantor Obligations [Line Items]
Letter of Credit Facility Maximum Additional Amount Potentially Required to be Issued	168,000,000
Hybrid Letter of Credit \| Letter of Credit
Guarantor Obligations [Line Items]
Letter of Credit Facility Commitments that Can be Used for Issuance of Letters of Credit or Line of Credit Loan	1,615,000,000
Letter of Credit Facility Remaining Commitment	1,262,000,000
Hybrid Letter of Credit Subject to Material Adverse Change Clauses \| Letter of Credit
Guarantor Obligations [Line Items]
Letter of Credit Facility Commitments that Can be Used for Issuance of Letters of Credit or Line of Credit Loan	353,000,000
Financial guarantees
Guarantor Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	472,008,000	447,683,000
Financial guarantees \| Long-term variable-rate bonds
Guarantor Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	446,000,000	473,000,000
Financial guarantees \| Long-term fixed-rate bonds
Guarantor Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	73,000,000
Guarantee Obligations Unsecured	120,000,000
Other guarantees
Guarantor Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	115,018,000	117,118,000
Guarantor Obligations, Maximum Exposure, Undiscounted	116,000,000
Maturity Period	2025
Long Term Tax Exempt Loans
Guarantor Obligations [Line Items]
Letter of Credit Obligations Liquidity Provided to Member Carrying Value	$ 125,000,000
Maturity Period	2042

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

No definition available.

Name:	nru_GuaranteeObligationsUnsecured
Namespace Prefix:	nru_
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:	nru_GuaranteeObligationsUnsecuredCommitmentAsPercentageOfTotalCommitment
Namespace Prefix:	nru_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the portion of the guarantee liability based on contingent exposures that are both probable and reasonably estimable related to guarantees and liquidity obligations.

+ References

No definition available.

+ Details

Name:	nru_GuarantyLiabilitiesContingent
Namespace Prefix:	nru_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This item represents the 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

No definition available.

+ Details

Name:	nru_GuarantyLiabilitiesContingentAndNoncontingent
Namespace Prefix:	nru_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the amount of commitments that may be used for the issuance of letters of credit or line of credit loan advances, at the option of the borrower.

+ References

No definition available.

+ Details

Name:	nru_LetterOfCreditFacilityCommitmentsThatCanBeUsedForIssuanceOfLettersOfCreditOrLineOfCreditLoan
Namespace Prefix:	nru_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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:	nru_LetterOfCreditFacilityMaximumAdditionalAmountPotentiallyRequiredToBeIssued
Namespace Prefix:	nru_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the remaining commitment that may be advanced as long as the borrower is in compliance with the terms and conditions of the facility.

+ References

No definition available.

+ Details

Name:	nru_LetterOfCreditFacilityRemainingCommitment
Namespace Prefix:	nru_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the amount of bonds for which obligation as liquidity provider is in the form of a letter of credit.

+ References

No definition available.

+ Details

Name:	nru_LetterOfCreditObligationsLiquidityProvidedToMemberCarryingValue
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the amount of liquidity that is provided to the entity's member cooperatives, if the remarketing agents are unable to sell the bonds to other investors.

+ References

No definition available.

+ Details

Name:	nru_LiquidityProvidedToMemberCarryingValue
Namespace Prefix:	nru_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the period of maturity.

+ References

No definition available.

+ Details

Name:	nru_MaturityPeriod
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

+ Details

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

- Details

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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/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph (b)(1)

-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

+ 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/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.15)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.15)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 25

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=7661617&loc=d3e11049-110243

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 25

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=7661617&loc=d3e11019-110243

+ Details

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