Mortgage Loans TDRs (Details) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2016 USD ($) contracts	Sep. 30, 2015 USD ($) contracts	Sep. 30, 2016 USD ($) contracts	Sep. 30, 2015 USD ($) contracts
Financing Receivable, Modifications [Line Items]
Average term extension of a single-family modified loan	153 months	159 months	157 months	161 months
Average interest rate reduction of a single-family modified loan	0.82%	0.69%	0.76%	0.75%
Number of loans troubled debt restructurings activity \| contracts	15,934	17,112	52,319	63,063
Recorded investment troubled debt restructurings activity \| $	$ 2,216	$ 2,362	$ 7,271	$ 8,847
Single-family [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity \| contracts	15,932	17,109	52,313	63,056
Recorded investment troubled debt restructurings activity \| $	$ 2,211	$ 2,352	$ 7,221	$ 8,831
Single-family [Member] \| Primary [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity \| contracts	13,983	14,926	45,987	54,284
Recorded investment troubled debt restructurings activity \| $	$ 1,922	$ 2,021	$ 6,282	$ 7,443
Single-family [Member] \| Government [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity \| contracts	54	54	136	192
Recorded investment troubled debt restructurings activity \| $	$ 5	$ 6	$ 14	$ 22
Single-family [Member] \| Alt-A [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity \| contracts	1,578	1,805	5,112	7,127
Recorded investment troubled debt restructurings activity \| $	$ 227	$ 268	$ 735	$ 1,101
Single-family [Member] \| Other [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity \| contracts	317	324	1,078	1,453
Recorded investment troubled debt restructurings activity \| $	$ 57	$ 57	$ 190	$ 265
Multifamily [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity \| contracts	2	3	6	7
Recorded investment troubled debt restructurings activity \| $	$ 5	$ 10	$ 50	$ 16

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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=66008989&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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