Allowance for Loan Losses - Rollforward by Segment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	$ (5,629)	$ (10,552)
Benefit (provision) for loan losses	(254)	766
Write-offs	27	104
Recoveries	(40)	(3)
Other	(3)	57
Ending Balance	(5,899)	(9,628)
Single-family
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	(4,950)	(9,344)
Benefit (provision) for loan losses	(282)	671
Write-offs	27	71
Recoveries	(33)	(2)
Other	(3)	57
Ending Balance	(5,241)	(8,547)
Multifamily
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	(679)	(1,208)
Benefit (provision) for loan losses	28	95
Write-offs	0	33
Recoveries	(7)	(1)
Ending Balance	$ (658)	$ (1,081)