Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
ASSETS
Restricted cash (includes $27,515 and $23,982, respectively, related to consolidated trusts)	$ 32,542	$ 28,995
Accrued interest receivable, net (includes $7,169 and $7,271, respectively, related to consolidated trusts)	8,193us-gaap_InterestReceivable	8,319us-gaap_InterestReceivable
Other assets (includes cash pledged as collateral of $1,646 and $1,590, respectively)	1,646	1,590
Investments in securities:
Available-for-sale, at fair value (includes $596 and $998, respectively, related to consolidated trusts)	30,654	38,171
Liabilities:
Accrued interest payable (includes $8,282 and $8,276, respectively, related to consolidated trusts)	10,232	10,553
Other liabilities (includes $503 and $488, respectively, related to consolidated trusts)	12,019us-gaap_OtherLiabilities	15,441us-gaap_OtherLiabilities
Fannie Mae stockholders’ equity:
Senior preferred stock, 1,000,000 shares issued	1,000,000fnm_SeniorPreferredStockIssuedShares	1,000,000fnm_SeniorPreferredStockIssuedShares
Senior preferred stock, 1,000,000 shares outstanding	1,000,000	1,000,000
Preferred stock, 7,000,000 shares are authorized	700,000,000us-gaap_PreferredStockSharesAuthorized	700,000,000us-gaap_PreferredStockSharesAuthorized
Preferred stock, 555, 374,922 shares issued	555,374,922us-gaap_PreferredStockSharesIssued	555,374,922us-gaap_PreferredStockSharesIssued
Preferred stock, 555,374,922 shares outstanding	555,374,922us-gaap_PreferredStockSharesOutstanding	555,374,922us-gaap_PreferredStockSharesOutstanding
Common stock, no par value, no maximum authorization--1,308,762,703 shares issued	1,308,762,703us-gaap_CommonStockSharesIssued	1,308,762,703us-gaap_CommonStockSharesIssued
Common stock, no par value, no maximum authorization--1,158,082,750 and 1,158,080,657 shares outstanding, respectively	1,158,082,750us-gaap_CommonStockSharesOutstanding	1,158,080,657us-gaap_CommonStockSharesOutstanding
Treasury stock, at cost, 150,679,953 and 150,682,046 shares, respectively	150,679,953us-gaap_TreasuryStockShares	150,682,046us-gaap_TreasuryStockShares
Fannie Mae [Member]
Liabilities:
Debt at fair value	6,403	1,308
Consolidated Trusts [Member]
ASSETS
Restricted cash (includes $27,515 and $23,982, respectively, related to consolidated trusts)	27,515	23,982
Accrued interest receivable, net (includes $7,169 and $7,271, respectively, related to consolidated trusts)	7,169	7,271
Investments in securities:
Available-for-sale, at fair value (includes $596 and $998, respectively, related to consolidated trusts)	596	998
Mortgage loans:
Loans held for investment, at amortized cost of consolidated trusts (includes $15,629 and $14,268, respectively, at fair value)	15,629	14,268
Loans held for investment, at amortized cost of consolidated trusts (includes loans pledged as collateral that may be sold or repledged of $0 and $442, respectively)	0	442
Liabilities:
Accrued interest payable (includes $8,282 and $8,276, respectively, related to consolidated trusts)	8,282	8,276
Debt at fair value	19,483	14,976
Other liabilities (includes $503 and $488, respectively, related to consolidated trusts)	$ 503	$ 488

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