Details of the Allowance for Credit Losses on Off-Balance Sheet Credit Exposure (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 147	$ 51	$ 81	$ 51
(Benefit) provision for credit losses	14	1	85	3
Charge-offs	(1)	(1)	(6)	(3)
Other	(6)	0	(6)	0
Ending balance	154	51	154	51
Single Family
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	57	46	57	46
Multifamily
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	$ 97	$ 5	$ 97	$ 5

Amount of other addition (reduction) in allowance reserve for credit loss.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of off balance sheet credit exposures that have been written off from both receivables and allowance reserve for credit loss.

+ References

No definition available.

+ Details

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- Definition

Amount of expected credit loss for credit exposure on off-balance-sheet commitment, including but not limited to, loan commitment, standby letter of credit, financial guarantee not accounted for as insurance. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121611286&loc=d3e11927-110247

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=121599878&loc=SL82919202-210446

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of expense (reversal of expense) for expected credit loss for off-balance sheet credit exposure. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447

+ Details

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Period Type:	duration

- References

No definition available.

+ Details

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- Details

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- Details

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