Short-Term Borrowings and Long-Term Debt Characteristics of Debt (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Long-term Debt by Year of Maturity [Abstract]
Total long-term debt	$ 3,115,583,000,000us-gaap_LongTermDebt	$ 3,160,074,000,000us-gaap_LongTermDebt
Fannie Mae [Member]
Long-Term Debt [Line Items]
Face amount	464,600,000,000	534,300,000,000
Outstanding debt		168,400,000,000
Long-term Debt by Year of Maturity [Abstract]
2015	64,655,000,000
2016	59,124,000,000
2017	79,193,000,000
2018	47,452,000,000
2019	32,564,000,000
Thereafter	72,443,000,000
Total long-term debt	355,431,000,000	457,139,000,000
Net unamortized discount, fair value adjustments and other cost basis adjustments	4,100,000,000	4,800,000,000
Fannie Mae [Member] \| Zero-Coupon Debt [Member]
Long-Term Debt [Line Items]
Face amount	116,700,000,000	86,800,000,000
Effective interest rate	0.77%	1.29%
Fannie Mae [Member] \| Callable [Member]
Long-Term Debt [Line Items]
Outstanding debt	115,000,000,000
Consolidated Trusts [Member]
Long-term Debt by Year of Maturity [Abstract]
Total long-term debt	2,760,152,000,000	2,702,935,000,000
Earlier of Contractual Maturity or Next Call Date [Member]
Long-term Debt by Year of Maturity [Abstract]
Total long-term debt	3,115,583,000,000
Earlier of Contractual Maturity or Next Call Date [Member] \| Fannie Mae [Member]
Long-term Debt by Year of Maturity [Abstract]
2015	173,495,000,000
2016	56,851,000,000
2017	52,598,000,000
2018	23,169,000,000
2019	17,964,000,000
Thereafter	31,354,000,000
Total long-term debt	355,431,000,000
Earlier of Contractual Maturity or Next Call Date [Member] \| Consolidated Trusts [Member]
Long-term Debt by Year of Maturity [Abstract]
Total long-term debt	$ 2,760,152,000,000

Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer.

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Face (par) amount of debt instrument at time of issuance.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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The amount of debt discount (net of debt premium) that was originally recognized at the issuance of the instrument that has yet to be amortized.

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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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