Name:	fnm_DefinedContributionPlanEmployersContributionPercent
Namespace Prefix:	fnm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Percentage credited to the defined contribution plan for the participant's eligible compensation that exceeds the IRS annual limit that vests after 3 years of service.

No definition available.

Name:	fnm_DefinedContributionPlanEmployersContributionThatVestGraduallyPercent
Namespace Prefix:	fnm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Percentage credited to the defined contribution plan for the participant's eligible compensation that exceeds the IRS annual limit that vests immediately.

No definition available.

Name:	fnm_DefinedContributionPlanEmployersContributionThatVestImmediatelyPercent
Namespace Prefix:	fnm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

The period over which an employer's matching contributions to a defined contribution plan vest.

No definition available.

Name:	fnm_DefinedContributionPlanEmployersMatchingContributionVestingPeriod
Namespace Prefix:	fnm_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

The period over which an employer's unmatching contributions to a defined contribution plan vest.

No definition available.

Name:	fnm_DefinedContributionPlanEmployersNonMatchingContributionVestingPeriod
Namespace Prefix:	fnm_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

The percentage contributed by the employer to a defined contribution plan that does not require employees to also contribute to the plan.

No definition available.

Name:	fnm_DefinedContributionPlanMaximumEmployerNonMatchingContributionPercent
Namespace Prefix:	fnm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Maximum amount per employee, by the terms of the plan, that the employer may contribute to a defined contribution plan in relation to the employee's salary.

No definition available.

Name:	fnm_DefinedContributionPlanMaximumRatioOfEligibleCompensationToBaseSalary
Namespace Prefix:	fnm_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	fnm_DefinedContributionPlansDisclosureLineItems
Namespace Prefix:	fnm_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The amount of the cost recognized during the period for defined contribution plans.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 70

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 11

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

No definition available.

Name:	us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Percentage of employer's matching contributions to a defined contribution plan that vests in a given year.

No definition available.