Allowance for Credit Losses - Components of the Allowance (Details) - USD ($) $ in Millions	Sep. 30, 2026	Jun. 30, 2026	Dec. 31, 2025	Sep. 30, 2025	Jun. 30, 2025	Dec. 31, 2024
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Abstract]
Allowance for loan losses	$ (9,415)		$ (8,364)
Other	(244)		(228)
Total	(9,659)	$ (8,753)	(8,592)	$ (8,477)	$ (8,471)	$ (7,886)
Single-family
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Abstract]
Allowance for loan losses	(6,694)		(6,056)
Other	(231)		(216)
Total	(6,925)	(6,345)	(6,272)	(6,064)	(5,985)	(5,487)
Multifamily
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Abstract]
Allowance for loan losses	(2,721)		(2,308)
Other	(13)		(12)
Total	$ (2,734)	$ (2,408)	$ (2,320)	$ (2,413)	$ (2,486)	$ (2,399)