Mortgage Loans TDRs (Details) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2017 USD ($) contracts	Jun. 30, 2016 USD ($) contracts	Jun. 30, 2017 USD ($) contracts	Jun. 30, 2016 USD ($) contracts
Financing Receivable, Modifications [Line Items]
Average term extension of a single-family modified loan	155 months	159 months	154 months	159 months
Average interest rate reduction of a single-family modified loan	0.67%	0.72%	0.80%	0.73%
Number of loans troubled debt restructurings activity \| contracts	15,795	16,831	34,965	36,385
Recorded investment troubled debt restructurings activity \| $	$ 2,206	$ 2,375	$ 4,852	$ 5,055
Single-family [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity \| contracts	15,792	16,827	34,962	36,381
Recorded investment troubled debt restructurings activity \| $	$ 2,189	$ 2,330	$ 4,835	$ 5,010
Single-family [Member] \| Primary [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity \| contracts	14,148	14,814	31,383	32,004
Recorded investment troubled debt restructurings activity \| $	$ 1,945	$ 2,028	$ 4,308	$ 4,360
Single-family [Member] \| Government [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity \| contracts	45	28	106	82
Recorded investment troubled debt restructurings activity \| $	$ 4	$ 3	$ 10	$ 9
Single-family [Member] \| Alt-A [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity \| contracts	1,328	1,623	2,893	3,534
Recorded investment troubled debt restructurings activity \| $	$ 194	$ 238	$ 418	$ 508
Single-family [Member] \| Other [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity \| contracts	271	362	580	761
Recorded investment troubled debt restructurings activity \| $	$ 46	$ 61	$ 99	$ 133
Multifamily [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity \| contracts	3	4	3	4
Recorded investment troubled debt restructurings activity \| $	$ 17	$ 45	$ 17	$ 45

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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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