Mortgage Loans TDRs with Sub Defaults (Details) $ in Millions	3 Months Ended
Mar. 31, 2018 USD ($) contracts	Mar. 31, 2017 USD ($) contracts
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default \| contracts	5,705	5,314
Recorded investment troubled debt restructurings subsequent default \| $	$ 852	$ 761
Single-family [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default \| contracts	5,704	5,313
Recorded investment troubled debt restructurings subsequent default \| $	$ 850	$ 757
Single-family [Member] \| Primary [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default \| contracts	4,818	4,479
Recorded investment troubled debt restructurings subsequent default \| $	$ 701	$ 621
Single-family [Member] \| Government [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default \| contracts	14	19
Recorded investment troubled debt restructurings subsequent default \| $	$ 2	$ 2
Single-family [Member] \| Alt-A [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default \| contracts	677	614
Recorded investment troubled debt restructurings subsequent default \| $	$ 109	$ 96
Single-family [Member] \| Other [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default \| contracts	195	201
Recorded investment troubled debt restructurings subsequent default \| $	$ 38	$ 38
Multifamily [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default \| contracts	1	1
Recorded investment troubled debt restructurings subsequent default \| $	$ 2	$ 4

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Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953682-111524

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Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

+ References

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