Name:	fnm_Loans30To59DaysPastDuePercentageOfUnpaidPrincipalBalance
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Represents the percentage of unpaid principal balance comprised of loans 60 to 89 days past due. Calculated based on the aggregate unpaid principal balance for the category indicated, divided by the respective book of business.

No definition available.

Name:	fnm_Loans60To89DaysPastDuePercentageOfUnpaidPrincipalBalance
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Represents the percentage unpaid principal balance comprised of single-family loans greater than or equal to 90 days past due or multifamily loans greater than or equal to 60 days past due. Calculated based on the aggregate unpaid principal balance for the category indicated, divided by the respective book of business.

No definition available.

Name:	fnm_LoansSeriouslyDelinquentPercentageOfUnpaidPrincipalBalance
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Represents the percentage of loans that are 30 to 59 days past due. Calculated based on the number of loans in the delinquency bucket indicated, divided by the total number of loans in the respective category.

No definition available.

Name:	fnm_NumberOfLoans30To59DaysPastDuePercentage
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Represents the percentage of loans that are 60 to 89 days past due. Calculated based on the number of loans in the delinquency bucket indicated, divided by the total number of loans in the respective category.

No definition available.

Name:	fnm_NumberOfLoans60To89DaysPastDuePercentage
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Represents the percentage of single-family loans greater than or equal to 90 days past due or multifamily loans greater than or equal to 60 days past due, included in each category. Calculated based on the number of loans in the delinquency bucket indicated, divided by the total number of loans in the respective category.

No definition available.

Name:	fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
Namespace Prefix:	fnm_
Data Type:	dtr-types1:percentItemType
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Represents the percentage of unpaid principal balance of loans, by category.

No definition available.

Name:	fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
Namespace Prefix:	fnm_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

Represents the number of days past due required for a loan to be considered seriously delinquent.

No definition available.

Name:	fnm_SeriousDelinquencyDayspastdue1
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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.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 20
-Name Accounting Standards Codification
-Section 40
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481628/310-20-40-7

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481990/310-10-45-2

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