Mortgage Loans (Nonaccrual Loans (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Amortized cost in nonaccrual loans	$ 28,574	$ 27,981
Financing Receivable, Nonaccrual, Interest Income	583
Single-Family [Member]
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	739
Financing Receivable, Accrued Interest, Writeoff	206
Amortized cost in nonaccrual loans	26,505	27,546
Financing Receivable, Nonaccrual, Interest Income	524
Single-Family [Member] \| Fixed Rate Residential Mortgage [Member]
Amortized cost in nonaccrual loans	22,907	23,427
Financing Receivable, Nonaccrual, Interest Income	461
Single-Family [Member] \| FixedRateResidentialMortgage15yearMember [Member]
Amortized cost in nonaccrual loans	853	858
Financing Receivable, Nonaccrual, Interest Income	15
Single-Family [Member] \| Adjustable Rate Loans [Member]
Amortized cost in nonaccrual loans	270	288
Single-Family [Member] \| Other [Member]
Amortized cost in nonaccrual loans	2,475	2,973
Financing Receivable, Nonaccrual, Interest Income	43
Single-Family [Member] \| Adjustable Rate Residential Mortgage [Member]
Financing Receivable, Nonaccrual, Interest Income	5
Multifamily [Member]
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	19
Financing Receivable, Accrued Interest, Writeoff	19
Amortized cost in nonaccrual loans	2,069	$ 435
Financing Receivable, Nonaccrual, Interest Income	$ 59

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
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL120267969-210447

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Amount of interest income on financing receivable on nonaccrual status.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 16
-Subparagraph (b)
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Amount of financing receivable on nonaccrual status.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5111-111524

Reference 2: 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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-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919258-210447

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Reflects the amount of additional interest income that would have been recorded if impaired or nonperforming loans were instead current, in compliance with their original terms, and outstanding throughout the reporting period or since origination (if held for part of the period).

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 310
-SubTopic 40
-Section 50
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