Consolidated Statements of Cash Flows	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 49,423,000,000	$ 60,260,000,000	$ 62,177,000,000
Cash flows provided by (used in) operating activities:
Net income	15,959,000,000	2,463,000,000	12,313,000,000
Reconciliation of net income to net cash used in operating activities:
Amortization of cost basis adjustments	(5,949,000,000)	(6,641,000,000)	(6,821,000,000)
Benefit for credit losses	(3,309,000,000)	(2,041,000,000)	(2,155,000,000)
Valuation gains	(911,000,000)	(1,573,000,000)	(472,000,000)
Current and deferred federal income taxes	3,680,000,000	14,369,000,000	4,309,000,000
Net gains related to the disposition of acquired property and preforeclosure sales, including credit enhancements	(1,785,000,000)	(2,426,000,000)	(3,124,000,000)
Net change in trading securities	(5,454,000,000)	4,511,000,000	(3,005,000,000)
Other, net	440,000,000	(406,000,000)	(1,778,000,000)
Interest Paid, Excluding Capitalized Interest, Operating Activities	(423,000,000)	(4,043,000,000)	(247,000,000)
Net cash provided by (used in) operating activities	2,248,000,000	4,213,000,000	(980,000,000)
Cash flows provided by investing activities:
Proceeds from maturities and paydowns of trading securities held for investment	182,000,000	1,206,000,000	1,840,000,000
Proceeds from sales of trading securities held for investment	96,000,000	241,000,000	1,618,000,000
Proceeds from maturities and paydowns of available-for-sale securities	695,000,000	2,009,000,000	2,927,000,000
Proceeds from sales of available-for-sale securities	760,000,000	1,990,000,000	11,378,000,000
Purchases of loans held for investment	(172,155,000,000)	(189,593,000,000)	(233,935,000,000)
Advances to lenders	(108,294,000,000)	(123,687,000,000)	(140,147,000,000)
Proceeds from disposition of acquired property and preforeclosure sales	9,321,000,000	12,221,000,000	16,115,000,000
Net change in federal funds sold and securities purchased under agreements to resell or similar arrangements	(13,468,000,000)	10,945,000,000	(3,065,000,000)
Other, net	78,000,000	641,000,000	116,000,000
Net cash provided by investing activities	150,853,000,000	184,408,000,000	231,053,000,000
Cash flows used in financing activities:
Payments of cash dividends on senior preferred stock to Treasury	(9,372,000,000)	(12,015,000,000)	(9,624,000,000)
Proceeds from senior preferred stock purchase agreement with Treasury	3,687,000,000	0	0
Other, net	63,000,000	6,000,000	14,000,000
Net cash used in financing activities	(163,938,000,000)	(190,538,000,000)	(213,449,000,000)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect	(10,837,000,000)	(1,917,000,000)	16,624,000,000
Cash and cash equivalents at end of period	25,557,000,000	32,110,000,000
Cash paid during the period for:
Interest	110,415,000,000	109,480,000,000	104,318,000,000
Income taxes	460,000,000	3,090,000,000	1,711,000,000
Non-cash activities:
Net mortgage loans acquired by assuming debt	231,478,000,000	258,312,000,000	275,710,000,000
Net transfers from mortgage loans of Fannie Mae to mortgage loans of consolidated trusts	185,310,000,000	193,809,000,000	223,705,000,000
Transfers from advances to lenders to loans held for investment of consolidated trusts	102,865,000,000	118,282,000,000	130,886,000,000
Net transfers from mortgage loans to acquired property	8,131,000,000	10,262,000,000	13,768,000,000
Transfers of mortgage loans from held for investment to held for sale	21,960,000,000	12,886,000,000	3,878,000,000
Fannie Mae [Member]
Cash flows provided by investing activities:
Proceeds from repayments of loans acquired as held for investment	15,082,000,000	22,557,000,000	25,294,000,000
Proceeds from sales of loans acquired as held for investment	17,511,000,000	10,241,000,000	5,222,000,000
Cash flows used in financing activities:
Proceeds from the issuance of debt	789,355,000,000	1,034,742,000,000	982,272,000,000
Payments to redeem debt	(834,366,000,000)	(1,082,427,000,000)	(1,042,861,000,000)
Consolidated Trusts [Member]
Cash flows provided by investing activities:
Proceeds from repayments of loans acquired as held for investment	401,045,000,000	435,637,000,000	543,690,000,000
Cash flows used in financing activities:
Proceeds from the issuance of debt	357,846,000,000	383,793,000,000	437,392,000,000
Payments to redeem debt	$ (471,151,000,000)	$ (514,637,000,000)	$ (580,642,000,000)