Mortgage Loans - Loans in Mortgage Portfolio (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2023	Dec. 31, 2022
Loans in Mortgage Portfolio [Line Items]
Total unpaid principal balance of mortgage loans	$ 4,106,757		$ 4,106,757			$ 4,102,632
Cost basis and fair value adjustments, net	39,557		39,557			41,729
Allowance for loan losses for HFI loans	(7,656)	$ (8,671)	(7,656)	$ (8,671)	$ (8,026)	(8,730)	$ (9,982)	$ (11,347)
Total mortgage loans	4,138,658		4,138,658			4,135,631
Accrued interest receivable, net	11,277		11,277			10,724
Single-family
Loans in Mortgage Portfolio [Line Items]
Allowance for loan losses for HFI loans	(5,086)	(6,640)	(5,086)	(6,640)	$ (5,703)	(6,671)	$ (7,990)	$ (9,443)
Amortized cost		3,100	1,272
Lower of cost or fair value adjustment at time of redesignation		(638)	(139)
Allowance reversed at time of redesignation	5	47	8
Single-family
Loans in Mortgage Portfolio [Line Items]
Total unpaid principal balance of mortgage loans	3,630,285		3,630,285			3,641,385
Purchase of HFI loans:	93,114	89,228	241,180	245,870
Amortized cost	820	3,122		3,122
Lower of cost or fair value adjustment at time of redesignation	(101)	(638)		(638)
Allowance reversed at time of redesignation				47
Amortized cost	77	372	77	372
Unpaid principal balance	14	0	2,345	1,842
Realized gains (losses), net	0	0	13	17
Multifamily
Loans in Mortgage Portfolio [Line Items]
Total unpaid principal balance of mortgage loans	476,472		476,472			461,247
Purchase of HFI loans:	13,153	$ 16,415	32,492	$ 41,761
Mortgage loans
Loans in Mortgage Portfolio [Line Items]
Accrued interest receivable, net	$ 10,900		$ 10,900			$ 10,400