Allowance for Loan Losses - Changes in Allowance (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Allowance for Loan Losses [Line Items]
Beginning balance	$ (8,026)	$ (9,982)	$ (8,730)	$ (11,347)
Benefit (provision) for loan losses	(14)	635	453	1,706
Write-offs	455	751	882	1,100
Recoveries	(71)	(56)	(261)	(169)
Other	0	(19)	0	39
Ending balance	(7,656)	(8,671)	(7,656)	(8,671)
Single-family
Allowance for Loan Losses [Line Items]
Beginning balance	(5,703)	(7,990)	(6,671)	(9,443)
Benefit (provision) for loan losses	409	718	1,278	2,121
Write-offs	231	699	487	794
Recoveries	(23)	(48)	(180)	(151)
Other	0	(19)	0	39
Ending balance	(5,086)	(6,640)	(5,086)	(6,640)
Multifamily
Allowance for Loan Losses [Line Items]
Beginning balance	(2,323)	(1,992)	(2,059)	(1,904)
Benefit (provision) for loan losses	(423)	(83)	(825)	(415)
Write-offs	224	52	395	306
Recoveries	(48)	(8)	(81)	(18)
Ending balance	$ (2,570)	$ (2,031)	$ (2,570)	$ (2,031)