Mortgage Loans Non-accrual Loans (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Nonaccrual [Line Items]
Recorded investment in nonaccrual loans	$ 25,714	$ 25,714	$ 28,069	$ 27,981
Financing Receivable, Nonaccrual, Interest Income	76	355
Single-family [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	219	573
Recorded investment in nonaccrual loans	25,367	25,367	27,753	27,546
Financing Receivable, Nonaccrual, Interest Income	76	352
Financing Receivable, Accrued Interest, Writeoff	33	165
Single-family [Member] \| FixedRateResidentialMortgage15yearMember
Financing Receivable, Nonaccrual [Line Items]
Recorded investment in nonaccrual loans	780	780	844	858
Financing Receivable, Nonaccrual, Interest Income	2	9
Single-family [Member] \| Other [Member]
Financing Receivable, Nonaccrual [Line Items]
Recorded investment in nonaccrual loans	2,438	2,438	2,851	2,973
Financing Receivable, Nonaccrual, Interest Income	5	31
Single-family [Member] \| Adjustable Rate Residential Mortgage [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Nonaccrual, Interest Income	1	3
Single-family [Member] \| Adjustable Rate Loans
Financing Receivable, Nonaccrual [Line Items]
Recorded investment in nonaccrual loans	247	247	275	288
Single-family [Member] \| Fixed Rate Residential Mortgage
Financing Receivable, Nonaccrual [Line Items]
Recorded investment in nonaccrual loans	21,902	21,902	23,783	23,427
Financing Receivable, Nonaccrual, Interest Income	68	309
Multifamily [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	8	9
Recorded investment in nonaccrual loans	347	347	$ 316	$ 435
Financing Receivable, Nonaccrual, Interest Income	0	3
Financing Receivable, Accrued Interest, Writeoff	$ 5	$ 7

Amount of writeoff of accrued interest on financing receivable recognized by reversing interest income.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 3D
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 16
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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
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-Section 50
-Paragraph 16
-Subparagraph (a)
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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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