Fair Value Fair Value of Financial Instruments (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Carrying Value [Member]
Financial assets [Abstract]
Cash and cash equivalents and restricted cash	$ 48,223,000,000	$ 89,036,000,000
Federal funds sold and securities purchased under agreements to resell or similar arrangements	38,975,000,000	32,500,000,000
Trading securities	30,768,000,000	40,695,000,000
Available-for-sale securities	38,171,000,000	63,181,000,000
Mortgage loans held for sale	380,000,000	464,000,000
Mortgage loans held for investment	3,025,860,000,000	2,948,942,000,000
Advances to lenders	3,727,000,000	7,592,000,000
Derivatives assets at fair value	2,073,000,000	435,000,000
Guaranty assets and buy-ups	267,000,000	327,000,000
Total assets	3,188,444,000,000	3,183,172,000,000
Financial liabilities [Abstract]
Derivative liabilities at fair value	1,469,000,000	705,000,000
Guaranty obligations	485,000,000	599,000,000
Total liabilities	3,236,477,000,000	3,190,821,000,000
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial assets [Abstract]
Cash and cash equivalents and restricted cash	36,633,000,000	75,786,000,000
Federal funds sold and securities purchased under agreements to resell or similar arrangements	0
Trading securities	16,306,000,000	17,950,000,000
Available-for-sale securities	0
Mortgage loans held for sale	0
Mortgage loans held for investment	0
Advances to lenders	0
Derivatives assets at fair value	0
Guaranty assets and buy-ups	0
Total assets	52,939,000,000	93,736,000,000
Financial liabilities [Abstract]
Derivative liabilities at fair value	0
Guaranty obligations	0
Total liabilities	0
Significant Other Observable Inputs (Level 2) [Member]
Financial assets [Abstract]
Cash and cash equivalents and restricted cash	11,590,000,000	13,250,000,000
Federal funds sold and securities purchased under agreements to resell or similar arrangements	38,975,000,000	32,500,000,000
Trading securities	11,688,000,000	20,459,000,000
Available-for-sale securities	19,159,000,000	38,147,000,000
Mortgage loans held for sale	185,000,000	267,000,000
Mortgage loans held for investment	2,599,667,000,000	2,567,022,000,000
Advances to lenders	3,165,000,000	6,936,000,000
Derivatives assets at fair value	10,430,000,000	16,051,000,000
Guaranty assets and buy-ups	0	0
Total assets	2,694,859,000,000	2,694,632,000,000
Financial liabilities [Abstract]
Derivative liabilities at fair value	10,734,000,000	22,590,000,000
Guaranty obligations	0	0
Total liabilities	3,231,253,000,000	3,347,367,000,000
Significant Unobservable Inputs (Level 3) [Member]
Financial assets [Abstract]
Cash and cash equivalents and restricted cash	0	0
Federal funds sold and securities purchased under agreements to resell or similar arrangements	0	0
Trading securities	2,774,000,000	2,286,000,000
Available-for-sale securities	19,012,000,000	25,034,000,000
Mortgage loans held for sale	195,000,000	208,000,000
Mortgage loans held for investment	392,355,000,000	466,594,000,000
Advances to lenders	523,000,000	572,000,000
Derivatives assets at fair value	65,000,000	175,000,000
Guaranty assets and buy-ups	706,000,000	692,000,000
Total assets	415,630,000,000	495,561,000,000
Financial liabilities [Abstract]
Derivative liabilities at fair value	105,000,000	161,000,000
Guaranty obligations	2,433,000,000	3,113,000,000
Total liabilities	19,611,000,000	23,984,000,000
Netting Adjustment [Member]
Financial assets [Abstract]
Cash and cash equivalents and restricted cash	0	0
Federal funds sold and securities purchased under agreements to resell or similar arrangements	0	0
Trading securities	0	0
Available-for-sale securities	0	0
Mortgage loans held for sale	0	0
Mortgage loans held for investment	0	0
Advances to lenders	0	0
Derivatives assets at fair value	(8,422,000,000)	(15,791,000,000)
Guaranty assets and buy-ups	0	0
Total assets	(8,422,000,000)	(15,791,000,000)
Financial liabilities [Abstract]
Derivative liabilities at fair value	(9,370,000,000)	(22,046,000,000)
Guaranty obligations	0	0
Total liabilities	(9,370,000,000)	(22,046,000,000)
Estimated Fair Value [Member]
Financial assets [Abstract]
Cash and cash equivalents and restricted cash	48,223,000,000	89,036,000,000
Federal funds sold and securities purchased under agreements to resell or similar arrangements	38,975,000,000	32,500,000,000
Trading securities	30,768,000,000	40,695,000,000
Available-for-sale securities	38,171,000,000	63,181,000,000
Mortgage loans held for sale	380,000,000	475,000,000
Mortgage loans held for investment	2,992,022,000,000	3,033,616,000,000
Advances to lenders	3,688,000,000	7,508,000,000
Derivatives assets at fair value	2,073,000,000	435,000,000
Guaranty assets and buy-ups	706,000,000	692,000,000
Total assets	3,155,006,000,000	3,268,138,000,000
Financial liabilities [Abstract]
Derivative liabilities at fair value	1,469,000,000	705,000,000
Guaranty obligations	2,433,000,000	3,113,000,000
Total liabilities	3,241,494,000,000	3,349,305,000,000
Fannie Mae [Member]
Financial liabilities [Abstract]
Long-term debt	1,308,000,000	793,000,000
Fannie Mae [Member] | Carrying Value [Member]
Financial assets [Abstract]
Mortgage loans held for investment	259,638,000,000	305,025,000,000
Financial liabilities [Abstract]
Short-term debt	72,295,000,000	105,233,000,000
Long-term debt	457,139,000,000	510,631,000,000
Fannie Mae [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial assets [Abstract]
Mortgage loans held for investment	0
Financial liabilities [Abstract]
Short-term debt	0
Long-term debt	0
Fannie Mae [Member] | Significant Other Observable Inputs (Level 2) [Member]
Financial assets [Abstract]
Mortgage loans held for investment	29,920,000,000	39,018,000,000
Financial liabilities [Abstract]
Short-term debt	72,304,000,000	105,253,000,000
Long-term debt	463,991,000,000	534,516,000,000
Fannie Mae [Member] | Significant Unobservable Inputs (Level 3) [Member]
Financial assets [Abstract]
Mortgage loans held for investment	215,960,000,000	232,170,000,000
Financial liabilities [Abstract]
Short-term debt	0	0
Long-term debt	1,557,000,000	1,056,000,000
Fannie Mae [Member] | Netting Adjustment [Member]
Financial assets [Abstract]
Mortgage loans held for investment	0	0
Financial liabilities [Abstract]
Short-term debt	0	0
Long-term debt	0	0
Fannie Mae [Member] | Estimated Fair Value [Member]
Financial assets [Abstract]
Mortgage loans held for investment	245,880,000,000	271,188,000,000
Financial liabilities [Abstract]
Short-term debt	72,304,000,000	105,253,000,000
Long-term debt	465,548,000,000	535,572,000,000
Consolidated Trusts [Member]
Financial assets [Abstract]
Mortgage loans held for investment	14,268,000,000	10,800,000,000
Financial liabilities [Abstract]
Long-term debt	14,976,000,000	11,647,000,000
Consolidated Trusts [Member] | Carrying Value [Member]
Financial assets [Abstract]
Mortgage loans held for investment	2,766,222,000,000	2,643,917,000,000
Financial liabilities [Abstract]
Short-term debt	2,154,000,000	3,483,000,000
Long-term debt	2,702,935,000,000	2,570,170,000,000
Consolidated Trusts [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial assets [Abstract]
Mortgage loans held for investment	0
Financial liabilities [Abstract]
Short-term debt	0
Long-term debt	0
Consolidated Trusts [Member] | Significant Other Observable Inputs (Level 2) [Member]
Financial assets [Abstract]
Mortgage loans held for investment	2,569,747,000,000	2,528,004,000,000
Financial liabilities [Abstract]
Short-term debt	0	0
Long-term debt	2,684,224,000,000	2,685,008,000,000
Consolidated Trusts [Member] | Significant Unobservable Inputs (Level 3) [Member]
Financial assets [Abstract]
Mortgage loans held for investment	176,395,000,000	234,424,000,000
Financial liabilities [Abstract]
Short-term debt	2,154,000,000	3,483,000,000
Long-term debt	13,362,000,000	16,171,000,000
Consolidated Trusts [Member] | Netting Adjustment [Member]
Financial assets [Abstract]
Mortgage loans held for investment	0	0
Financial liabilities [Abstract]
Short-term debt	0	0
Long-term debt	0	0
Consolidated Trusts [Member] | Estimated Fair Value [Member]
Financial assets [Abstract]
Mortgage loans held for investment	2,746,142,000,000	2,762,428,000,000
Financial liabilities [Abstract]
Short-term debt	2,154,000,000	3,483,000,000
Long-term debt	2,697,586,000,000	2,701,179,000,000
Home Affordable Refinance Program (HARP) Loans [Member]
Financial Instruments [Line Items]
Loans Receivable Refinanced under Home Affordable Refinance Program, Fair Value Disclosure	306,900,000,000	255,200,000,000
Fair Value Estimation Process [Member] | Home Affordable Refinance Program (HARP) Loans [Member]
Financial Instruments [Line Items]
Change In Estimated Fair Value Resulting From Change In Prinicipal Market	$ 11,500,000,000	$ 7,600,000,000