Allowance for Loan Losses - Changes in Allowance (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Allowance for Loan Losses [Line Items]
Beginning balance	$ (8,730)	$ (11,347)
Benefit (provision) for loan losses	182	(176)
Write-offs	248	279
Recoveries	(79)	(85)
Other	0	(6)
Ending balance	(8,379)	(11,335)
Single-family
Allowance for Loan Losses [Line Items]
Beginning balance	(6,671)	(9,443)
Benefit (provision) for loan losses	339	4
Write-offs	115	42
Recoveries	(58)	(76)
Other	0	(6)
Ending balance	(6,275)	(9,479)
Multifamily
Allowance for Loan Losses [Line Items]
Beginning balance	(2,059)	(1,904)
Benefit (provision) for loan losses	(157)	(180)
Write-offs	133	237
Recoveries	(21)	(9)
Ending balance	$ (2,104)	$ (1,856)