Mortgage Loans Held for Portfolio (Mortgage Loans Held for Portfolio) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable, Unpaid Principal Balance	$ 9,414	$ 9,208
Loans and Leases Receivable, Unamortized Premiums	128	125
Loans and Leases Receivable, Unamortized Discounts	(4)	(4)
Loans and Leases Receivable, Hedging Basis Adjustment	9	6
Loans and Leases Receivable, Net of Deferred Income	9,547	9,335
Loans and Leases Receivable, Net Amount	9,546	9,334
Single Family [Member] \| Fixed rate, long-term single family mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable, Unpaid Principal Balance	8,335	8,192
Single Family [Member] \| Fixed rate, medium-term single family mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable, Unpaid Principal Balance	1,079	1,016
Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Loss	$ (1)	$ (1)

Reflects the cumulative amount of hedging adjustments that are being amortized into income as an adjustment of yield.

No definition available.

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- Definition

Reflects the cumulative amount of discounts from the face amount of loans that are being amortized into income as an adjustment of yield.

+ References

No definition available.

+ Details

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- Definition

Reflects the cumulative amount of premiums over the face amount of loans that are being amortized into income as an adjustment to yield.

+ 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

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 210
-Section S99
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- Definition

Amount, before allowance and fees, of loans and leases receivable. Excludes loans and leases covered under loss sharing agreements.

+ References

+ Details

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- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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+ Details

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- Definition

Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
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