Financial Guarantees Financial Guarantees and Maximum Recovery (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2019	Dec. 31, 2018
Financial Guarantees and Maximum Recovery [Line Items]
Maximum Exposure	$ 19,584	$ 21,125
Guaranty Obligation	161	160
Maximum Recovery	8,963	9,522
Unconsolidated VIEs [Member] \| Unconsolidated Fannie Mae MBS [Member]
Financial Guarantees and Maximum Recovery [Line Items]
Maximum Exposure	6,603	7,278
Guaranty Obligation	26	30
Maximum Recovery	6,354	6,811
Unconsolidated VIEs [Member] \| Other guaranty arrangements [Member]
Financial Guarantees and Maximum Recovery [Line Items]
Maximum Exposure	12,981	13,847
Guaranty Obligation	135	130
Maximum Recovery	2,609	$ 2,711
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] \| Unconsolidated VIEs [Member]
Financial Guarantees and Maximum Recovery [Line Items]
Single security, Freddie Mac issued securities backing unconsolidated Fannie Mae securities	$ 28,900
Minimum [Member]
Financial Guarantees and Maximum Recovery [Line Items]
Contractual terms of our guarantees	1 day
Maximum [Member]
Financial Guarantees and Maximum Recovery [Line Items]
Contractual terms of our guarantees	33 years

Represents the original contractual term of guarantees.

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- Definition

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

+ References

No definition available.

+ Details

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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.

+ References

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=118943654&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=118943654&loc=d3e12069-110248

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