Mortgage Loans - Loans in Mortgage Portfolio (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025	Dec. 31, 2025
Loans in Mortgage Portfolio [Line Items]
Total UPB of mortgage loans	$ 4,093,544		$ 4,093,544		$ 4,095,866
Cost basis and fair value adjustments, net	22,502		22,502		31,811
Allowance for loan losses for HFI loans	(9,415)		(9,415)		(8,364)
Total mortgage loans	4,106,631		4,106,631		4,119,313
Accrued interest receivable, net	12,567		12,567		11,689
Single-family
Loans in Mortgage Portfolio [Line Items]
Total UPB of mortgage loans	3,557,836		3,557,836		3,570,904
Purchase of HFI loans:	87,500	$ 90,175	296,610	$ 237,369
Amortized cost	197	823	738	1,527
Lower of cost or fair value adjustment at time of redesignation	(14)	(97)	(96)	(187)
Allowance reversed at time of redesignation	7
Allowance reversed at time of redesignation		6	4	26
UPB	541	309	541	969
Realized gains (losses), net	(2)	(7)	(2)	0
Multifamily
Loans in Mortgage Portfolio [Line Items]
Total UPB of mortgage loans	535,708		535,708		524,962
Purchase of HFI loans:	14,272	$ 18,508	45,121	$ 46,658
Mortgage loans
Loans in Mortgage Portfolio [Line Items]
Accrued interest receivable, net	$ 11,800		$ 11,800		$ 11,300