Fair Value - Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Fair Value Measurement [Domain]
Financial assets:
Derivative assets, gross amount offset	$ (218)	$ (154)
Financial liabilities:
Derivative liabilities, gross amount offset	(4,227)	(4,662)
Total Fair Value	646	696
Mortgage loans held for investment, net of allowance for loan losses	3,433	3,645
Derivative assets at fair value	145	175
Derivative assets, gross amount offset	(218)	(154)
Derivative liabilities at fair value	297	168
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents, including restricted cash and cash equivalents	36,235	32,991
Securities purchased under agreements to resell	0	0
Trading securities	48,207	46,898
Total Fair Value	0	0
Mortgage loans held for sale	0	0
Mortgage loans held for investment, net of allowance for loan losses	0	0
Advances to lenders	0	0
Derivative assets at fair value	0	0
Guaranty assets and buy-ups	0	0
Total financial assets	84,442	79,889
Financial liabilities:
Derivative liabilities at fair value	0	0
Guaranty obligations	0	0
Total financial liabilities	0	0
Significant Other Observable Inputs (Level 2)
Financial assets:
Cash and cash equivalents, including restricted cash and cash equivalents	43,200	54,850
Securities purchased under agreements to resell	33,050	14,565
Trading securities	2,350	3,184
Total Fair Value	55	62
Mortgage loans held for sale	31	48
Mortgage loans held for investment, net of allowance for loan losses	3,455,655	3,437,979
Advances to lenders	3,483	1,502
Derivative assets at fair value	281	300
Guaranty assets and buy-ups	0	0
Total financial assets	3,538,105	3,512,490
Financial liabilities:
Derivative liabilities at fair value	4,454	4,764
Guaranty obligations	0	0
Total financial liabilities	3,674,709	3,648,996
Significant Unobservable Inputs (Level 3)
Financial assets:
Cash and cash equivalents, including restricted cash and cash equivalents	0	0
Securities purchased under agreements to resell	0	0
Trading securities	28	47
Total Fair Value	591	634
Mortgage loans held for sale	495	2,029
Mortgage loans held for investment, net of allowance for loan losses	166,079	171,857
Advances to lenders	0	0
Derivative assets at fair value	82	29
Guaranty assets and buy-ups	162	166
Total financial assets	167,437	174,762
Financial liabilities:
Derivative liabilities at fair value	70	66
Guaranty obligations	65	66
Total financial liabilities	40,276	42,840
Fannie Mae
Financial liabilities:
Long-term debt:	884	1,161
Fannie Mae | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial liabilities:
Short-term debt:	0	0
Long-term debt:	0	0
Fannie Mae | Significant Other Observable Inputs (Level 2)
Financial liabilities:
Short-term debt:	15,619	10,208
Long-term debt:	121,057	122,066
Fannie Mae | Significant Unobservable Inputs (Level 3)
Financial liabilities:
Short-term debt:	0	0
Long-term debt:	574	558
Consolidated Trusts
Financial liabilities:
Long-term debt:	15,172	16,260
Consolidated Trusts | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial liabilities:
Long-term debt:	0	0
Consolidated Trusts | Significant Other Observable Inputs (Level 2)
Financial liabilities:
Long-term debt:	3,533,579	3,511,958
Consolidated Trusts | Significant Unobservable Inputs (Level 3)
Financial liabilities:
Long-term debt:	39,567	42,150
Carrying Value
Financial assets:
Cash and cash equivalents, including restricted cash and cash equivalents	79,435	87,841
Securities purchased under agreements to resell	33,050	14,565
Trading securities	50,585	50,129
Total Fair Value	646	696
Mortgage loans held for sale	513	2,033
Mortgage loans held for investment, net of allowance for loan losses	4,120,612	4,112,403
Advances to lenders	3,483	1,502
Derivative assets at fair value	145	175
Guaranty assets and buy-ups	78	87
Total financial assets	4,288,547	4,269,431
Financial liabilities:
Derivative liabilities at fair value	297	168
Guaranty obligations	85	94
Total financial liabilities	4,232,732	4,222,150
Carrying Value | Fannie Mae
Financial liabilities:
Short-term debt:	15,628	10,204
Long-term debt:	122,068	123,964
Carrying Value | Consolidated Trusts
Financial liabilities:
Long-term debt:	4,094,654	4,087,720
Fair Value
Financial assets:
Cash and cash equivalents, including restricted cash and cash equivalents	79,435	87,841
Securities purchased under agreements to resell	33,050	14,565
Trading securities	50,585	50,129
Total Fair Value	646	696
Mortgage loans held for sale	526	2,077
Mortgage loans held for investment, net of allowance for loan losses	3,621,734	3,609,836
Advances to lenders	3,483	1,502
Derivative assets at fair value	145	175
Guaranty assets and buy-ups	162	166
Total financial assets	3,789,766	3,766,987
Financial liabilities:
Derivative liabilities at fair value	297	168
Guaranty obligations	65	66
Total financial liabilities	3,710,758	3,687,174
Fair Value | Fannie Mae
Financial liabilities:
Short-term debt:	15,619	10,208
Long-term debt:	121,631	122,624
Fair Value | Consolidated Trusts
Financial liabilities:
Long-term debt:	$ 3,573,146	$ 3,554,108