Allowance for Loan Losses - Changes in Allowance (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Allowance for Loan Losses [Line Items]
Beginning balance	$ (7,532)	$ (8,379)	$ (7,707)	$ (8,730)
(Provision) benefit for loan losses	(912)	285	(927)	467
Write-offs	283	179	533	427
Recoveries	(86)	(111)	(146)	(190)
Ending balance	(8,247)	(8,026)	(8,247)	(8,026)
Single-family
Allowance for Loan Losses [Line Items]
Beginning balance	(5,178)	(6,275)	(5,319)	(6,671)
(Provision) benefit for loan losses	(707)	530	(723)	869
Write-offs	161	141	350	256
Recoveries	(53)	(99)	(85)	(157)
Ending balance	(5,777)	(5,703)	(5,777)	(5,703)
Multifamily
Allowance for Loan Losses [Line Items]
Beginning balance	(2,354)	(2,104)	(2,388)	(2,059)
(Provision) benefit for loan losses	(205)	(245)	(204)	(402)
Write-offs	122	38	183	171
Recoveries	(33)	(12)	(61)	(33)
Ending balance	$ (2,470)	$ (2,323)	$ (2,470)	$ (2,323)