Condensed Consolidated Balance Sheets (Parenthetical) (Unaudited) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
ASSETS
Restricted cash	$ 57,231	$ 67,919
Investments in securities:
Available-for-sale, at fair value	60,329	63,181
Mortgage loans:
Loans held for sale, at lower of cost or fair value	455	464
Accrued interest receivable, net	9,160	9,176
Cash pledged as collateral included in other assets	1,289	1,222
Liabilities:
Accrued interest payable	11,163	11,303
Other liabilities	14,383	14,378
Fannie Mae stockholders' equity (deficit):
Senior preferred stock issued	1,000,000	1,000,000
Senior preferred stock outstanding	1,000,000	1,000,000
Preferred stock authorized	700,000,000	700,000,000
Preferred stock issued	555,374,922	555,374,922
Preferred stock outstanding	555,374,922	555,374,922
Common stock issued	1,308,762,703	1,308,762,703
Common stock outstanding	1,158,077,970	1,158,077,970
Treasury stock, shares	150,684,733	150,684,733
Fannie Mae [Member]
Liabilities:
Debt at fair value	770	793
Consolidated Trusts [Member]
ASSETS
Restricted cash	51,847	61,976
Investments in securities:
Available-for-sale, at fair value	762	935
Mortgage loans:
Loans held for sale, at lower of cost or fair value	104	72
Mortgage loans held for investment, at amortized cost	12,602	10,800
Loans pledged as collateral that may be sold or repledged included in loans held for investment, at amortized cost	859	943
Accrued interest receivable, net	7,801	7,567
Liabilities:
Accrued interest payable	8,435	8,645
Debt at fair value	13,345	11,647
Other liabilities	$ 406	$ 1,059