Allowance for Loan Losses Rollforward by Segment (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Allowance for Loan Losses [Roll Forward]
Beginning balance	$ (11,482)	$ (16,812)	$ (14,203)	$ (19,084)
Benefit (provision) for loan losses	(1,843)	(710)	(3,689)	(1,922)
Charge-offs	272	509	1,215	1,710
Recoveries	(9)	(68)	(71)	(192)
Other	0	(2)	(6)	(19)
Ending balance	(9,376)	(15,663)	(9,376)	(15,663)
Single-family [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	(11,210)	(16,602)	(13,969)	(18,849)
Benefit (provision) for loan losses	(1,826)	(724)	(3,712)	(1,916)
Charge-offs	270	509	1,209	1,705
Recoveries	(8)	(65)	(68)	(189)
Other	0	(2)	(6)	(19)
Ending balance	(9,122)	(15,436)	(9,122)	(15,436)
Multifamily [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	(272)	(210)	(234)	(235)
Benefit (provision) for loan losses	(17)	14	23	(6)
Charge-offs	2	0	6	5
Recoveries	(1)	(3)	(3)	(3)
Ending balance	(254)	$ (227)	$ (254)	$ (227)
Change in Accounting Estimate, Type [Domain]
Allowance for Loan Losses [Roll Forward]
Benefit (provision) for loan losses	$ 850

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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- Definition

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

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- Definition

The reserve to cover probable credit losses related to specifically identified fixed maturity real estate loans as well as probable credit losses inherent in the remainder of that loan portfolio.

+ References

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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- Definition

Amount of credit loss expense (reversal of expense) for financing receivable.

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