Variable Interest Entities Additional Information (Details) - Consolidated variable interest entities $ in Millions	May 31, 2019 USD ($) director vote
Variable Interest Entity [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted \| $	$ 27
RTFC
Variable Interest Entity [Line Items]
Number of votes by each member for election of directors	1
NCSC
Variable Interest Entity [Line Items]
Number of directors for whom nomination process is controlled \| director	1
Number of votes by each member for election of directors	1

Represents the number of directors for whom nomination process is controlled.

No definition available.

Name:	nru_NumberOfDirectorsForWhomNominationProcessIsControlled
Namespace Prefix:	nru_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the number of votes by each member for election of directors to the board.

+ References

No definition available.

+ Details

Name:	nru_NumberOfVotesPerMemberForElectionOfDirectors
Namespace Prefix:	nru_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- 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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=118943654&loc=d3e12069-110248

+ Details

Name:	us-gaap_GuaranteeObligationsMaximumExposure
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

No definition available.

+ Details

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

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=nru_RuralTelephoneFinanceCooperativeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=nru_NationalCooperativeServicesCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: