Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows provided by (used in) operating activities:
Net income	$ 11,805	$ 14,160	$ 15,959
Reconciliation of net income to net cash provided by (used in) operating activities:
Amortization of cost basis adjustments	(9,190)	(6,002)	(5,949)
Benefit for credit losses	678	(4,011)	(3,309)
Valuation gains	(2,618)	(1,809)	(911)
Current and deferred federal income taxes	3,152	1,517	3,680
Net gains related to the disposition of acquired property and preforeclosure sales, including credit enhancements	(924)	(917)	(1,785)
Net change in accrued interest receivable	(2,749)	332	204
Net change in servicer advances	932	(67)	(206)
Other, net	(225)	(363)	442
Net change in trading securities	(73,659)	(1,630)	(5,454)
Interest Paid, Excluding Capitalized Interest, Operating Activities	(136)	(5,964)	(423)
Net cash provided by (used in) operating activities	(72,934)	(4,754)	2,248
Cash flows provided by investing activities:
Proceeds from maturities and paydowns of trading securities held for investment	47	58	182
Proceeds from sales of trading securities held for investment	110	49	96
Proceeds from maturities and paydowns of available-for-sale securities	364	469	695
Proceeds from sales of available-for-sale securities	361	537	760
Purchases of loans held for investment	(766,699)	(261,808)	(172,155)
Advances to lenders	(339,043)	(141,395)	(108,294)
Proceeds from disposition of acquired property and preforeclosure sales	5,991	7,425	9,321
Net change in federal funds sold and securities purchased under agreements to resell or similar arrangements	(14,622)	19,360	(13,468)
Other, net	287	(80)	78
Net cash provided by investing activities	26,685	207,052	150,853
Cash flows used in financing activities:
Payments of cash dividends on senior preferred stock to Treasury	0	(5,601)	(9,372)
Proceeds from senior preferred stock purchase agreement with Treasury	0	0	3,687
Other, net	(510)	480	63
Net cash used in financing activities	100,465	(190,314)	(163,938)
Net increase (decrease) in cash, cash equivalents and restricted cash	54,216	11,984	(10,837)
Cash, cash equivalents and restricted cash at beginning of period	61,407	49,423	60,260
Cash, cash equivalents and restricted cash at end of period	115,623	61,407	49,423
Cash paid during the period for:
Interest	113,878	121,542	110,415
Income taxes	3,950	1,900	460
Non-cash activities:
Net mortgage loans acquired by assuming debt	369,733	273,174	231,478
Net transfers from mortgage loans of Fannie Mae to mortgage loans of consolidated trusts	709,451	248,463	185,310
Transfers from advances to lenders to loans held for investment of consolidated trusts	318,426	128,272	102,865
Net transfers from mortgage loans to acquired property	3,940	6,681	8,131
Fannie Mae [Member]
Cash flows provided by investing activities:
Proceeds from repayments of loans acquired as held for investment	10,672	12,508	15,082
Proceeds from sales of loans acquired as held for investment	8,744	17,794	17,511
Cash flows used in financing activities:
Proceeds from the issuance of debt	580,220	789,572	789,355
Payments to redeem debt	(472,795)	(834,294)	(834,366)
Consolidated Trusts [Member]
Cash flows provided by investing activities:
Proceeds from repayments of loans acquired as held for investment	1,120,473	552,135	401,045
Cash flows used in financing activities:
Proceeds from the issuance of debt	1,091,242	435,235	357,846
Payments to redeem debt	$ (1,097,692)	$ (575,706)	$ (471,151)