Allowance for Credit Losses - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
May 31, 2024	May 31, 2023
Loan Loss Allowance
Allowance for loan loss, rounded amount	$ 49	$ 53
Financing receivable, allowance coverage ratios	0.14%	0.16%
Financing receivable, allowance for credit loss, period increase (decrease)	$ (4)
Credit reserve for unadvanced loan commitments	$ 1	$ 1
Asset-Specific Allowance
Loan Loss Allowance
Financing receivable, allowance coverage ratios	30.71%	21.39%
Financing receivable, allowance for credit loss, period increase (decrease)	$ (8)
Collective Allowance
Loan Loss Allowance
Financing receivable, allowance coverage ratios	0.09%	0.08%
Financing receivable, allowance for credit loss, period increase (decrease)	$ 4

Credit Reserve for Unadvanced Loan Commitments

No definition available.

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

- Definition

Financing Receivable, Allowance for Credit Loss, Rounded Amount

+ References

No definition available.

+ Details

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

- Definition

Percentage of allowance for credit loss to total financing receivable outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph a
-Subparagraph (1)
-Publisher SEC

+ Details

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Namespace Prefix:	srt_
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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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph c
-Publisher SEC

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

+ Details

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

- Definition

Amount, excluding accrued interest, of increase (decrease) in allowance for credit loss on 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 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

+ Details

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- Details

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- Details

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