Guarantees and Other Off-Balance Sheet Credit Exposures - Financial Guarantees (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Guarantor Obligations [Line Items]
Outstanding balance of the guarantor advance	$ 400	$ 300
Guarantees of Fannie Mae securities
Guarantor Obligations [Line Items]
UPB	98,370	104,120
Maximum Exposure	98,370	104,120
Recognized Liability	$ 0	$ 0
Maximum Remaining Term	36 years	37 years
Other Guarantees
Guarantor Obligations [Line Items]
UPB	$ 64	$ 79
Maximum Exposure	399	472
Recognized Liability	$ 0	$ 0
Maximum Remaining Term	30 years	30 years
Single-family
Guarantor Obligations [Line Items]
UPB	$ 37,237	$ 37,979
Maximum Exposure	31,816	32,411
Recognized Liability	549	540
Single-family | Securitization products
Guarantor Obligations [Line Items]
UPB	30,025	30,038
Maximum Exposure	24,604	24,470
Recognized Liability	$ 453	$ 413
Maximum Remaining Term	40 years	39 years
Single-family | Other mortgage-related guarantees
Guarantor Obligations [Line Items]
UPB	$ 7,212	$ 7,941
Maximum Exposure	7,212	7,941
Recognized Liability	$ 96	$ 127
Maximum Remaining Term	26 years	27 years
Multifamily
Guarantor Obligations [Line Items]
UPB	$ 342,575	$ 365,954
Maximum Exposure	309,499	328,442
Recognized Liability	3,961	4,583
Multifamily | Securitization products
Guarantor Obligations [Line Items]
UPB	332,572	355,108
Maximum Exposure	299,507	317,611
Recognized Liability	$ 3,629	$ 4,219
Maximum Remaining Term	34 years	35 years
Multifamily | Other mortgage-related guarantees
Guarantor Obligations [Line Items]
UPB	$ 10,003	$ 10,846
Maximum Exposure	9,992	10,831
Recognized Liability	$ 332	$ 364
Maximum Remaining Term	33 years	34 years