Financial Guarantees - Financial Guarantees and Maximum Recovery (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2021	Dec. 31, 2020
Financial Guarantees and Maximum Recovery [Line Items]
Contractual terms of our guarantees	31 years
Maximum Exposure	$ 14,736	$ 16,252
Guaranty Obligation	108	127
Maximum Recovery	6,027	6,664
Unconsolidated Fannie Mae MBS \| Unconsolidated VIEs
Financial Guarantees and Maximum Recovery [Line Items]
Maximum Exposure	3,964	4,424
Guaranty Obligation	17	18
Maximum Recovery	3,847	4,226
Other guaranty arrangements \| Unconsolidated VIEs
Financial Guarantees and Maximum Recovery [Line Items]
Maximum Exposure	10,772	11,828
Guaranty Obligation	91	109
Maximum Recovery	2,180	2,438
Other agency \| Unconsolidated VIEs
Financial Guarantees and Maximum Recovery [Line Items]
Single security, Freddie Mac issued securities backing unconsolidated Fannie Mae securities	$ 190,200	$ 137,300

[Line Items] for Financial Guarantees and Maximum Recovery [Table]

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- Definition

Portion of Freddie Mac securities backing commingled Fannie Mae-issued structured securities.

+ References

No definition available.

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- Definition

Represents the maximum amount we could recover through available credit enhancements and recourse with third parties on guarantees recognized in our on and off balance sheets. Recoverability of such credit enhancements and recourse is subject to, among other factors, our mortgage insurers' and financial guarantors' ability to meet their obligations to us.

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No definition available.

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- 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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=124440162&loc=d3e12069-110248

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- 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=124440162&loc=d3e12069-110248

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- Definition

Describe the approximate term of the guarantee or each group of similar guarantees.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=124440162&loc=d3e12069-110248

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