Mortgage Loans TDRs with Sub Defaults (Details) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018 USD ($) contracts	Sep. 30, 2017 USD ($) contracts	Sep. 30, 2018 USD ($) contracts	Sep. 30, 2017 USD ($) contracts
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default \| contracts	4,310	5,730	14,583	16,073
Recorded investment troubled debt restructurings subsequent default \| $	$ 624	$ 816	$ 2,150	$ 2,296
Single-family [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default \| contracts	4,309	5,730	14,581	16,072
Recorded investment troubled debt restructurings subsequent default \| $	$ 622	$ 816	$ 2,146	$ 2,292
Single-family [Member] \| Primary [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default \| contracts	3,720	4,900	12,372	13,617
Recorded investment troubled debt restructurings subsequent default \| $	$ 519	$ 684	$ 1,774	$ 1,894
Single-family [Member] \| Government [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default \| contracts	8	25	37	69
Recorded investment troubled debt restructurings subsequent default \| $	$ 0	$ 3	$ 4	$ 8
Single-family [Member] \| Alt-A [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default \| contracts	438	627	1,703	1,857
Recorded investment troubled debt restructurings subsequent default \| $	$ 74	$ 95	$ 275	$ 288
Single-family [Member] \| Other [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default \| contracts	143	178	469	529
Recorded investment troubled debt restructurings subsequent default \| $	$ 29	$ 34	$ 93	$ 102
Multifamily [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default \| contracts	1	0	2	1
Recorded investment troubled debt restructurings subsequent default \| $	$ 2	$ 0	$ 4	$ 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://fasb.org/us-gaap/role/ref/legacyRef
-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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