Mortgage Loans TDRs (Details) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2016 USD ($) contracts	Jun. 30, 2015 USD ($) contracts	Jun. 30, 2016 USD ($) contracts	Jun. 30, 2015 USD ($) contracts
Financing Receivable, Modifications [Line Items]
Average term extension of a single-family modified loan	159 months	162 months	159 months	162 months
Average interest rate reduction of a single-family modified loan	0.72%	0.77%	0.73%	0.77%
Number of loans troubled debt restructurings activity \| contracts	16,831	21,088	36,385	45,951
Recorded investment troubled debt restructurings activity \| $	$ 2,375	$ 2,981	$ 5,055	$ 6,485
Single-family [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity \| contracts	16,827	21,087	36,381	45,947
Recorded investment troubled debt restructurings activity \| $	$ 2,330	$ 2,980	$ 5,010	$ 6,479
Single-family [Member] \| Primary [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity \| contracts	14,814	17,951	32,004	39,358
Recorded investment troubled debt restructurings activity \| $	$ 2,028	$ 2,477	$ 4,360	$ 5,422
Single-family [Member] \| Government [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity \| contracts	28	64	82	138
Recorded investment troubled debt restructurings activity \| $	$ 3	$ 8	$ 9	$ 16
Single-family [Member] \| Alt-A [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity \| contracts	1,623	2,533	3,534	5,322
Recorded investment troubled debt restructurings activity \| $	$ 238	$ 395	$ 508	$ 833
Single-family [Member] \| Other [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity \| contracts	362	539	761	1,129
Recorded investment troubled debt restructurings activity \| $	$ 61	$ 100	$ 133	$ 208
Multifamily [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity \| contracts	4	1	4	4
Recorded investment troubled debt restructurings activity \| $	$ 45	$ 1	$ 45	$ 6

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- Definition

The following represents the average term extension (disclosed in months) resulting from loan modifications.

+ References

No definition available.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953676-111524

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Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

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