Allowance for Loan Losses - Changes in Allowance (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Allowance for Loan Losses [Line Items]
Beginning balance	$ (8,247)	$ (8,026)	$ (7,707)	$ (8,730)
(Provision) benefit for loan losses	(332)	(14)	(1,259)	453
Write-offs	405	455	938	882
Recoveries	(72)	(71)	(218)	(261)
Ending balance	(8,246)	(7,656)	(8,246)	(7,656)
Single-family
Allowance for Loan Losses [Line Items]
Beginning balance	(5,777)	(5,703)	(5,319)	(6,671)
(Provision) benefit for loan losses	(269)	409	(992)	1,278
Write-offs	238	231	588	487
Recoveries	(47)	(23)	(132)	(180)
Ending balance	(5,855)	(5,086)	(5,855)	(5,086)
Multifamily
Allowance for Loan Losses [Line Items]
Beginning balance	(2,470)	(2,323)	(2,388)	(2,059)
(Provision) benefit for loan losses	(63)	(423)	(267)	(825)
Write-offs	167	224	350	395
Recoveries	(25)	(48)	(86)	(81)
Ending balance	$ (2,391)	$ (2,570)	$ (2,391)	$ (2,570)