Allowance for Loan Losses - Changes in Allowance (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Allowance for Loan Losses [Line Items]
Beginning balance	$ (8,379)	$ (11,335)	$ (8,730)	$ (11,347)
Benefit (provision) for loan losses	285	1,247	467	1,071
Write-offs	179	70	427	349
Recoveries	(111)	(28)	(190)	(113)
Other	0	64	0	58
Ending balance	(8,026)	(9,982)	(8,026)	(9,982)
Single-family
Allowance for Loan Losses [Line Items]
Beginning balance	(6,275)	(9,479)	(6,671)	(9,443)
Benefit (provision) for loan losses	530	1,399	869	1,403
Write-offs	141	53	256	95
Recoveries	(99)	(27)	(157)	(103)
Other	0	64	0	58
Ending balance	(5,703)	(7,990)	(5,703)	(7,990)
Multifamily
Allowance for Loan Losses [Line Items]
Beginning balance	(2,104)	(1,856)	(2,059)	(1,904)
Benefit (provision) for loan losses	(245)	(152)	(402)	(332)
Write-offs	38	17	171	254
Recoveries	(12)	(1)	(33)	(10)
Ending balance	$ (2,323)	$ (1,992)	$ (2,323)	$ (1,992)