Federal National Mortgage Association (FNMA) 10-K 14 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2017	Jan. 31, 2018	Jun. 30, 2017
Entity Information [Line Items]
Entity Registrant Name	FEDERAL NATIONAL MORTGAGE ASSOCIATION FANNIE MAE
Entity Central Index Key	310,522
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		1,158,087,567
Entity Public Float			$ 2.7
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
ASSETS
Cash and cash equivalents	$ 32,110	$ 25,224
Restricted cash (includes $22,132 and $31,536, respectively, related to consolidated trusts)	28,150	36,953
Federal funds sold and securities purchased under agreements to resell or similar arrangements	19,470	30,415
Investments in securities:
Trading, at fair value (includes $747 and $1,277, respectively, pledged as collateral)	34,679	40,562
Available-for-sale, at fair value (includes $87 and $107, respectively, related to consolidated trusts)	4,843	8,363
Total investments in securities	39,522	48,925
Mortgage loans:
Loans held for sale, at lower of cost or fair value	4,988	2,899
Loans held for investment, at amortized cost (includes $10,596 and $12,057, respectively, at fair value)	3,192,621	3,100,319
Allowance for loan losses	(19,084)	(23,465)
Total loans held for investment, net of allowance	3,173,537	3,076,854
Total mortgage loans	3,178,525	3,079,753
Deferred tax assets, net	17,350	33,530
Accrued interest receivable, net (includes $7,560 and $7,064, respectively, related to consolidated trusts)	8,133	7,737
Acquired property, net	3,220	4,489
Other assets	19,049	20,942
Total assets	3,345,529	3,287,968
Liabilities:
Accrued interest payable (includes $8,598 and $8,285, respectively, related to consolidated trusts)	9,682	9,431
Other liabilities (includes $492 and $390, respectively, related to consolidated trusts)	9,479	10,150
Total liabilities	3,349,215	3,281,897
Commitments and contingencies (Note 16)	0	0
Fannie Mae stockholders’ equity (deficit):
Senior preferred stock, 1,000,000 shares issued and outstanding	117,149	117,149
Preferred stock, 700,000,000 shares are authorized— 555,374,922 shares issued and outstanding	19,130	19,130
Common stock, no par value, no maximum authorization—1,308,762,703 shares issued and 1,158,087,567 and 1,158,082,750 shares outstanding, respectively	687	687
Accumulated deficit	(133,805)	(124,253)
Accumulated other comprehensive income	553	759
Treasury stock, at cost, 150,675,136 and 150,679,953 shares, respectively	(7,400)	(7,401)
Total stockholders’ equity (deficit) (See Note 1: Senior Preferred Stock Purchase Agreement, Senior Preferred Stock and Warrant for information on our dividend obligation to Treasury)	(3,686)	6,071
Total liabilities and equity (deficit)	3,345,529	3,287,968
Fannie Mae [Member]
Mortgage loans:
Loans held for investment, at amortized cost (includes $10,596 and $12,057, respectively, at fair value)	162,809	204,318
Liabilities:
Debt (includes $8,186 and $9,582, respectively, of debt of Fannie Mae and $30,493 and $36,524, respectively, of debt of consolidated trusts, at fair value)	276,752	327,097
Consolidated Trusts [Member]
ASSETS
Restricted cash (includes $22,132 and $31,536, respectively, related to consolidated trusts)	22,132	31,536
Investments in securities:
Available-for-sale, at fair value (includes $87 and $107, respectively, related to consolidated trusts)	87	107
Mortgage loans:
Loans held for investment, at amortized cost (includes $10,596 and $12,057, respectively, at fair value)	3,029,812	2,896,001
Accrued interest receivable, net (includes $7,560 and $7,064, respectively, related to consolidated trusts)	7,560	7,064
Liabilities:
Accrued interest payable (includes $8,598 and $8,285, respectively, related to consolidated trusts)	8,598	8,285
Debt (includes $8,186 and $9,582, respectively, of debt of Fannie Mae and $30,493 and $36,524, respectively, of debt of consolidated trusts, at fair value)	3,053,302	2,935,219
Other liabilities (includes $492 and $390, respectively, related to consolidated trusts)	$ 492	$ 390

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
ASSETS
Restricted cash (includes $22,132 and $31,536, respectively, related to consolidated trusts)	$ 28,150	$ 36,953
Investments in securities:
Trading, at fair value (includes $747 and $1,277, respectively, pledged as collateral)	747	1,277
Available-for-sale, at fair value (includes $87 and $107, respectively, related to consolidated trusts)	4,843	8,363
Mortgage loans:
Loans held for investment, at amortized cost of consolidated trusts (includes $12,057 and $14,075, respectively, at fair value)	10,596	12,057
Accrued interest receivable, net (includes $7,560 and $7,064, respectively, related to consolidated trusts)	8,133	7,737
Liabilities:
Accrued interest payable (includes $8,598 and $8,285, respectively, related to consolidated trusts)	9,682	9,431
Other liabilities (includes $492 and $390, respectively, related to consolidated trusts)	$ 9,479	$ 10,150
Fannie Mae stockholders’ equity (deficit):
Senior preferred stock, 1,000,000 shares issued	1,000,000	1,000,000
Senior preferred stock, 1,000,000 shares outstanding	1,000,000	1,000,000
Preferred stock, 700,000,000 shares are authorized	700,000,000	700,000,000
Preferred stock, 555,374,922 shares issued	555,374,922	555,374,922
Preferred stock, 555,374,922 shares outstanding	555,374,922	555,374,922
Common stock, no par value, no maximum authorization, 1,308,762,703 shares issued	1,308,762,703	1,308,762,703
Common stock, no par value, no maximum authorization, 1,158,087,567 and 1,158,082,750 shares outstanding, respectively	1,158,087,567	1,158,082,750
Treasury stock, at cost, 150,675,136 and 150,679,953 shares, respectively	150,675,136	150,679,953
Consolidated Trusts [Member]
ASSETS
Restricted cash (includes $22,132 and $31,536, respectively, related to consolidated trusts)	$ 22,132	$ 31,536
Investments in securities:
Available-for-sale, at fair value (includes $87 and $107, respectively, related to consolidated trusts)	87	107
Mortgage loans:
Accrued interest receivable, net (includes $7,560 and $7,064, respectively, related to consolidated trusts)	7,560	7,064
Liabilities:
Accrued interest payable (includes $8,598 and $8,285, respectively, related to consolidated trusts)	8,598	8,285
Debt at fair value	30,493	36,524
Other liabilities (includes $492 and $390, respectively, related to consolidated trusts)	492	390
Fannie Mae [Member]
Liabilities:
Debt at fair value	$ 8,186	$ 9,582

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest income:
Trading securities	$ 706	$ 516	$ 444
Available-for-sale securities	335	620	1,156
Mortgage loans (includes $100,593, $95,266 and $97,971, respectively, related to consolidated trusts)	108,319	104,642	107,699
Other	496	243	143
Total interest income	109,856	106,021	109,442
Interest expense:
Short-term debt	(250)	(206)	(146)
Long-term debt (includes $82,580, $77,575 and $80,326, respectively, related to consolidated trusts)	(88,873)	(84,520)	(87,887)
Total interest expense	(89,123)	(84,726)	(88,033)
Net interest income	20,733	21,295	21,409
Benefit for credit losses	2,041	2,155	795
Net interest income after benefit for credit losses	22,774	23,450	22,204
Non-interest Income:
Investment gains, net	1,522	1,256	1,336
Fair value losses, net	(1,211)	(1,081)	(1,767)
Fee and other income	2,227	966	1,348
Non-interest income	2,538	1,141	917
Administrative expenses:
Salaries and employee benefits	(1,328)	(1,336)	(1,319)
Professional services	(933)	(955)	(984)
Other administrative expenses	(476)	(450)	(747)
Total administrative expenses	(2,737)	(2,741)	(3,050)
Foreclosed property expense	(521)	(644)	(1,629)
Temporary Payroll Cut Continuation Act of 2011 (“TCCA”) fees	(2,096)	(1,845)	(1,621)
Other expenses, net	(1,511)	(1,028)	(613)
Total expenses	(6,865)	(6,258)	(6,913)
Income before federal income taxes	18,447	18,333	16,208
Provision for federal income taxes	(15,984)	(6,020)	(5,253)
Net income	2,463	12,313	10,955
Total comprehensive income
Changes in unrealized gains on available-for-sale securities, net of reclassification adjustments and taxes	(206)	(642)	(763)
Other	0	(6)	(437)
Total other comprehensive loss	(206)	(648)	(326)
Total comprehensive income	2,257	11,665	10,629
Less: Comprehensive income attributable to noncontrolling interest	0	0	(1)
Total comprehensive income attributable to Fannie Mae	2,257	11,665	10,628
Less: Net income attributable to noncontrolling interest	0	0	(1)
Net income attributable to Fannie Mae	2,463	12,313	10,954
Dividends distributed or available for distribution to senior preferred stockholder	(8,944)	(12,236)	(11,216)
Net income (loss) attributable to common stockholders	$ (6,481)	$ 77	$ (262)
Earnings (loss) per share: Basic	$ (1.12)	$ 0.01	$ (0.05)
Earnings (loss) per share: Diluted	$ (1.12)	$ 0.01	$ (0.05)
Weighted-average common shares outstanding: Basic	5,762	5,762	5,762
Weighted-average common shares outstanding: Diluted	5,762	5,893	5,762

Consolidated Statements of Ope5

Consolidated Statements of Operations and Comprehensive Income (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Mortgage loans interest income	$ 108,319	$ 104,642	$ 107,699
Long-term debt interest expense	88,873	84,520	87,887
Consolidated Trusts [Member]
Mortgage loans interest income	100,593	95,266	97,971
Long-term debt interest expense	$ 82,580	$ 77,575	$ 80,326

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows provided by (used in) operating activities:
Net income	$ 2,463	$ 12,313	$ 10,955
Reconciliation of net income to net cash used in operating activities:
Amortization of cost basis adjustments	(6,641)	(6,821)	(6,298)
Benefit for credit losses	(2,041)	(2,155)	(795)
Valuation gains	(1,573)	(472)	(510)
Current and deferred federal income taxes	14,369	4,309	4,083
Net change in trading securities	4,511	(3,005)	(10,153)
Net gains related to the disposition of acquired property and preforeclosure sales, including credit enhancements	(2,426)	(3,124)	(3,055)
Other, net	(406)	(1,778)	(900)
Net cash provided by (used in) operating activities	8,256	(733)	(6,673)
Cash flows provided by investing activities:
Proceeds from maturities and paydowns of trading securities held for investment	1,206	1,840	768
Proceeds from sales of trading securities held for investment	241	1,618	1,104
Proceeds from maturities and paydowns of available-for-sale securities	2,009	2,927	4,394
Proceeds from sales of available-for-sale securities	1,990	11,378	8,249
Purchases of loans held for investment	(189,593)	(233,935)	(187,194)
Net change in restricted cash	8,803	(6,074)	1,663
Advances to lenders	(123,687)	(140,147)	(118,746)
Proceeds from disposition of acquired property and preforeclosure sales	12,221	16,115	20,757
Net change in federal funds sold and securities purchased under agreements to resell or similar arrangements	10,945	(3,065)	3,600
Other, net	641	116	527
Net cash provided by investing activities	193,211	224,979	248,324
Cash flows used in financing activities:
Payments of cash dividends on senior preferred stock to Treasury	(12,015)	(9,624)	(10,278)
Other, net	6	14	26
Net cash used in financing activities	(194,581)	(213,696)	(249,000)
Net increase (decrease) in cash and cash equivalents	6,886	10,550	(7,349)
Cash and cash equivalents at beginning of period	25,224	14,674	22,023
Cash and cash equivalents at end of period	32,110	25,224	14,674
Cash paid during the period for:
Interest	109,480	104,318	104,928
Income taxes	3,090	1,711	1,170
Non-cash activities:
Net mortgage loans acquired by assuming debt	258,312	275,710	220,168
Net transfers from mortgage loans of Fannie Mae to mortgage loans of consolidated trusts	193,809	223,705	175,104
Transfers from advances to lenders to loans held for investment of consolidated trusts	118,282	130,886	114,851
Net transfers from mortgage loans to acquired property	10,262	13,768	17,534
Transfers of mortgage loans from held for investment to held for sale	12,886	3,878	8,601
Fannie Mae [Member]
Cash flows provided by investing activities:
Proceeds from repayments of loans acquired as held for investment	22,557	25,294	25,776
Proceeds from sales of loans acquired as held for investment	10,241	5,222	3,196
Cash flows used in financing activities:
Proceeds from the issuance of debt	1,034,742	982,272	443,371
Payments to redeem debt	(1,086,470)	(1,043,108)	(518,575)
Consolidated Trusts [Member]
Cash flows provided by investing activities:
Proceeds from repayments of loans acquired as held for investment	435,637	543,690	484,230
Cash flows used in financing activities:
Proceeds from the issuance of debt	383,793	437,392	347,614
Payments to redeem debt	$ (514,637)	$ (580,642)	$ (511,158)

Consolidated Statements of Chan

Consolidated Statements of Changes in Equity (Deficit) - USD ($) shares in Millions, $ in Millions	Total	Senior Preferred Stock	Preferred Stock	Common Stock	Accumulated Deficit	Accumulated Other Comprehensive Income	Treasury Stock	Noncontrolling Interest
Balance (shares) at Dec. 31, 2014		1	556	1,158
Balance at Dec. 31, 2014	$ 3,720	$ 117,149	$ 19,130	$ 687	$ (127,618)	$ 1,733	$ (7,401)	$ 40
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Change in investment in noncontrolling interest	(12)							(12)
Comprehensive income:
Net income	10,955				10,954			1
Other comprehensive income, net of tax effect:
Changes in net unrealized gains on available-for-sale securities (net of tax of $151, $30 and $28, respectively)	(280)					(280)
Reclassification adjustment for gains included in net income (net of tax of $253, $316 and $139, respectively)	(483)					(483)
Prior service cost and actuarial gains, net of amortization for defined benefit plans (net of tax)	437					437
Other, net of tax	(437)
Total comprehensive income	10,629
Senior preferred stock dividends	(10,278)				(10,278)
Balance at Dec. 31, 2015	4,059	$ 117,149	$ 19,130	$ 687	(126,942)	1,407	(7,401)	29
Balance (shares) at Dec. 31, 2015		1	556	1,158
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Change in investment in noncontrolling interest	(29)							(29)
Comprehensive income:
Net income	12,313				12,313			0
Other comprehensive income, net of tax effect:
Changes in net unrealized gains on available-for-sale securities (net of tax of $151, $30 and $28, respectively)	(55)					(55)
Reclassification adjustment for gains included in net income (net of tax of $253, $316 and $139, respectively)	(587)					(587)
Other, net of tax	(6)					(6)
Total comprehensive income	11,665
Senior preferred stock dividends	(9,624)				(9,624)
Balance at Dec. 31, 2016	6,071	$ 117,149	$ 19,130	$ 687	(124,253)	759	(7,401)	0
Balance (shares) at Dec. 31, 2016		1	556	1,158
Comprehensive income:
Net income	2,463				2,463			0
Other comprehensive income, net of tax effect:
Changes in net unrealized gains on available-for-sale securities (net of tax of $151, $30 and $28, respectively)	53					53
Reclassification adjustment for gains included in net income (net of tax of $253, $316 and $139, respectively)	(259)					(259)
Other, net of tax	0
Total comprehensive income	2,257
Senior preferred stock dividends	(12,015)				(12,015)
Balance at Dec. 31, 2017	(3,686)	$ 117,149	$ 19,130	$ 687	$ (133,805)	$ 553	(7,400)	$ 0
Balance (shares) at Dec. 31, 2017		1	556	1,158
Other comprehensive income, net of tax effect:
Stockholders' Equity, Other	$ 1						$ 1

Consolidated Statements of Cha8

Consolidated Statements of Changes in Equity (Deficit) (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Changes in net unrealized gains on available-for-sale securities, net of tax	$ 28	$ 30	$ 151
Reclassification adjustment for gains included in net income, net of tax	$ 139	$ 316	$ 253

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Organization We are a stockholder-owned corporation organized and existing under the Federal National Mortgage Association Charter Act (the “Charter Act” or our “charter”). We are a government-sponsored enterprise, and we are subject to government oversight and regulation. Our regulators include the Federal Housing Finance Agency (“FHFA”), the U.S. Department of Housing and Urban Development (“HUD”), the U.S. Securities and Exchange Commission (“SEC”), and the U.S. Department of the Treasury (“Treasury”). The U.S. government does not guarantee our securities or other obligations. We operate in the secondary mortgage market, primarily working with lenders. We do not originate loans or lend money directly to consumers in the primary mortgage market. Instead, we securitize mortgage loans originated by lenders into Fannie Mae mortgage-backed securities (“MBS”) that we guarantee; purchase mortgage loans and mortgage-related securities, primarily for securitization and sale at a later date; and engage in other activities that increase the supply of affordable housing. We have two reportable business segments: Single-Family and Multifamily. The Single-Family business operates in the secondary mortgage market relating to loans secured by properties containing four or fewer residential dwelling units. The Multifamily business operates in the secondary mortgage market relating primarily to loans secured by properties containing five or more residential units. We describe the management reporting and allocation process used to generate our segment results in “ Note 10, Segment Reporting .” Conservatorship On September 7, 2008, the Secretary of the Treasury and the Director of FHFA announced several actions taken by Treasury and FHFA regarding Fannie Mae, which included: (1) placing us in conservatorship and (2) the execution of a senior preferred stock purchase agreement by our conservator, on our behalf, and Treasury, pursuant to which we issued to Treasury both senior preferred stock and a warrant to purchase common stock. Under the Federal Housing Enterprises Financial Safety and Soundness Act of 1992, as amended, including by the Federal Housing Finance Regulatory Reform Act of 2008 (together, the “GSE Act”), the conservator immediately succeeded to (1) all rights, titles, powers and privileges of Fannie Mae, and of any stockholder, officer or director of Fannie Mae with respect to Fannie Mae and its assets, and (2) title to the books, records and assets of any other legal custodian of Fannie Mae. The conservator has since delegated specified authorities to our Board of Directors and has delegated to management the authority to conduct our day-to-day operations. The conservator retains the authority to withdraw its delegations at any time. The conservator has the power to transfer or sell any asset or liability of Fannie Mae (subject to limitations and post-transfer notice provisions for transfers of qualified financial contracts) without any approval, assignment of rights or consent of any party. The GSE Act, however, provides that mortgage loans and mortgage-related assets that have been transferred to a Fannie Mae MBS trust must be held by the conservator for the beneficial owners of the Fannie Mae MBS and cannot be used to satisfy the general creditors of Fannie Mae. Neither the conservatorship nor the terms of our agreements with Treasury change our obligation to make required payments on our debt securities or perform under our mortgage guaranty obligations. The conservatorship has no specified termination date and there continues to be significant uncertainty regarding our future, including how long we will continue to exist in our current form, the extent of our role in the market, how long we will be in conservatorship, what form we will have and what ownership interest, if any, our current common and preferred stockholders will hold in us after the conservatorship is terminated and whether we will continue to exist following conservatorship. Under the GSE Act, FHFA must place us into receivership if the Director of FHFA makes a written determination that our assets are less than our obligations or if we have not been paying our debts, in either case, for a period of 60 days . In addition, the Director of FHFA may place us into receivership at his discretion at any time for other reasons set forth in the GSE Act, including if we are critically undercapitalized or if we are undercapitalized and have no reasonable prospect of becoming adequately capitalized. Should we be placed into receivership, different assumptions would be required to determine the carrying value of our assets, which could lead to substantially different financial results. We are not aware of any plans of FHFA to fundamentally change our business model or capital structure in the near term. Senior Preferred Stock Purchase Agreement, Senior Preferred Stock and Warrant Senior Preferred Stock Purchase Agreement On September 7, 2008, we, through FHFA in its capacity as conservator, entered into a senior preferred stock purchase agreement with Treasury. This agreement was amended and restated on September 26, 2008. The amended and restated agreement was subsequently amended on May 6, 2009, December 24, 2009 and August 17, 2012. On December 21, 2017, we, through FHFA, in its capacity as conservator, and Treasury entered into a letter agreement amending the dividend and liquidation preference provisions of the senior preferred stock we previously issued to Treasury. The December 2017 letter agreement was not accounted for as an extinguishment of the existing senior preferred stock. Pursuant to the senior preferred stock purchase agreement, Treasury has committed to provide us with funding as described below to help us maintain a positive net worth thereby avoiding the mandatory receivership trigger described above. As consideration for Treasury’s funding commitment, we issued one million shares of senior preferred stock and a warrant to purchase shares of our common stock to Treasury. As of December 31, 2017 and 2016 , we received a total of $ 116.1 billion from Treasury pursuant to the senior preferred stock purchase agreement. Because we had a net worth deficit of $ 3.7 billion as of December 31, 2017 , we expect the Director of FHFA will submit a request to Treasury on our behalf for $3.7 billion to eliminate our net worth deficit. After we receive these additional funds, we will have received a total of $119.8 billion from Treasury pursuant to the senior preferred stock purchase agreement. As of December 31, 2017 , the amount of remaining funding available to us under the senior preferred stock purchase agreement was $117.6 billion . After we receive the additional funds requested from Treasury to eliminate our net worth deficit as of December 31, 2017, the maximum amount of remaining funding under the agreement will be $113.9 billion . See “ Note 11, Equity (Deficit) ” for additional information about the senior preferred stock purchase agreement. Senior Preferred Stock The aggregate liquidation preference of the senior preferred stock was $120.1 billion as of December 31, 2017 , and will increase to $123.8 billion after we receive the $3.7 billion in additional funds from Treasury to eliminate our net worth deficit as of December 31, 2017. The liquidation preference of the senior preferred stock is subject to adjustment, as described in “ Note 11, Equity (Deficit) .” Treasury, as the holder of the senior preferred stock, is entitled to receive, when, as and if declared, out of legally available funds, cumulative quarterly cash dividends. The dividends we have paid to Treasury on the senior preferred stock during conservatorship have been declared by, and paid at the direction of, our conservator, acting as successor to the rights, titles, powers and privileges of the Board of Directors. We recognize a liability on our balance sheet for senior preferred stock dividends only upon their declaration by our conservator, at which point they become payable to the shareholder. The dividend provisions of the senior preferred stock have been amended twice since the senior preferred stock was originally issued: in August 2012 through an amendment to the senior preferred stock purchase agreement and in December 2017 through a letter agreement. See “ Note 11, Equity (Deficit) ” for a description of the dividend provisions of the senior preferred stock applicable for the periods shown in this report and for 2018 and thereafter. On December 29, 2017 , we paid Treasury a fourth quarter 2017 dividend of $648 million on the senior preferred stock. Because we had a net worth deficit of $3.7 billion as of December 31, 2017 , no dividend will be payable to Treasury on the senior preferred stock for the first quarter of 2018. Warrant On September 7, 2008, we issued a warrant to Treasury giving it the right to purchase, at a nominal price, shares of our common stock equal to 79.9% of the total common stock outstanding on a fully diluted basis on the date Treasury exercises the warrant. Treasury has the right to exercise the warrant, in whole or in part, at any time on or before September 7, 2028. We recorded the warrant at fair value in our stockholders’ equity as a component of additional paid-in-capital. The fair value of the warrant was calculated using the Black-Scholes Option Pricing Model. Since the warrant has an exercise price of $0.00001 per share, the model is insensitive to the risk-free rate and volatility assumptions used in the calculation and the share value of the warrant is equal to the price of the underlying common stock. We estimated that the fair value of the warrant at issuance was $3.5 billion based on the price of our common stock on September 8, 2008, which was after the dilutive effect of the warrant had been reflected in the market price. Subsequent changes in the fair value of the warrant are not recognized in our financial statements. If the warrant is exercised, the stated value of the common stock issued will be reclassified as “Common stock” in our consolidated balance sheets. Because the warrant’s exercise price per share is considered non-substantive (compared to the market price of our common stock), the warrant was determined to have characteristics of non-voting common stock, and thus is included in the computation of basic and diluted loss per share. The weighted-average shares of common stock outstanding for 2017 , 2016 and 2015 included shares of common stock that would be issuable upon full exercise of the warrant issued to Treasury. Impact of U.S. Government Support We continue to rely on support from Treasury to eliminate any net worth deficits we may experience in the future, which would otherwise trigger our being placed into receivership. Based on consideration of all the relevant conditions and events affecting our operations, including our reliance on the U.S. government, we continue to operate as a going concern and in accordance with our delegation of authority from FHFA. We fund our business primarily through the issuance of short-term and long-term debt securities in the domestic and international capital markets. Because debt issuance is our primary funding source, we are subject to “roll over,” or refinancing, risk on our outstanding debt. Our ability to issue long-term debt has been strong primarily due to actions taken by the federal government to support us. We believe that continued federal government support of our business, as well as our status as a government-sponsored enterprise, are essential to maintaining our access to debt funding. Changes or perceived changes in federal government support of our business without appropriate capitalization of the company could materially and adversely affect our liquidity, financial condition and results of operations. Changes or perceived changes in our status as a government-sponsored enterprise could also materially and adversely affect our liquidity, financial condition and results of operations. In addition, due to our reliance on the U.S. government’s support, our access to debt funding or the cost of debt funding also could be materially adversely affected by a change or perceived change in the creditworthiness of the U.S government. A downgrade in our credit ratings could reduce demand for our debt securities and increase our borrowing costs. Future changes or disruptions in the financial markets could significantly impact the amount, mix and cost of funds we obtain, which also could increase our liquidity and “roll over” risk and have a material adverse impact on our liquidity, financial condition and results of operations. Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). To conform to our current period presentation, we have reclassified certain amounts reported in our prior periods’ consolidated financial statements. Related Parties As a result of our issuance to Treasury of the warrant to purchase shares of Fannie Mae common stock equal to 79.9% of the total number of shares of Fannie Mae common stock, we and Treasury are deemed related parties. As of December 31, 2017 , Treasury held an investment in our senior preferred stock with an aggregate liquidation preference of $120.1 billion . FHFA’s control of both us and Freddie Mac has caused us, FHFA and Freddie Mac to be deemed related parties. In October 2013, Fannie Mae and Freddie Mac established Common Securitization Solutions, LLC (“CSS”), a jointly owned limited liability company to operate a common securitization platform; therefore, CSS is deemed a related party. Transactions with Treasury Our administrative expenses were reduced by $40 million , $57 million and $68 million for the years ended December 31, 2017 , 2016 and 2015 , respectively, due to reimbursements from Treasury and Freddie Mac for expenses incurred as program administrator for Treasury’s Home Affordable Modification Program (“HAMP”) and other initiatives under Treasury’s Making Home Affordable Program. During the years ended December 31, 2017 , 2016 and 2015 , we made tax payments of $3.1 billion , $1.7 billion and $1.2 billion , respectively, to the Internal Revenue Service (“IRS”), a bureau of Treasury. We received $51 million in interest from the IRS during the year ended December 31, 2017 related to income tax periods from 2007 through 2013. We received $7 million in interest from the IRS during the year ended December 31, 2016 related to income tax periods from 2007 and prior. We received a refund of $1.5 billion from the IRS during the year ended December 31, 2017 for income tax adjustments related to tax years 2007 through 2013. We received a refund of $277 million from the IRS during the year ended December 31, 2015 for income tax adjustments related to tax years 2004 through 2010. In 2009, we entered into a memorandum of understanding with Treasury, FHFA and Freddie Mac pursuant to which we agreed to provide assistance to state and local housing finance agencies (“HFAs”) through certain programs, including a new issue bond (“NIB”) program. As of December 31, 2017 , under the NIB program, Fannie Mae and Freddie Mac had $4.8 billion outstanding of pass-through securities backed by single-family and multifamily housing bonds issued by HFAs, which is less than 35% of the total original principal under the program, the amount of losses that Treasury would bear. Accordingly, we do not have a potential risk of loss under the NIB program. In December 2011, Congress enacted the TCCA which, among other provisions, requires that we increase our single-family guaranty fees by at least 10 basis points and remit this increase to Treasury. Effective April 1, 2012, the guaranty fee on all single-family residential mortgages delivered to Fannie Mae on or after that date was increased by 10 basis points. FHFA and Treasury have advised us to remit this fee increase to Treasury with respect to all loans acquired by us on or after April 1, 2012 and before January 1, 2022, and to continue to remit these amounts to Treasury on and after January 1, 2022 with respect to loans we acquired before this date until those loans are paid off or otherwise liquidated. The resulting fee revenue and expense are recorded in “Mortgage loans interest income” and “TCCA fees,” respectively, in our consolidated statements of operations and comprehensive income. We recognized $2.1 billion , $ 1.8 billion and $1.6 billion in TCCA fees during the years ended December 31, 2017 , 2016 and 2015 , respectively, of which $544 million and $487 million had not been remitted as of December 31, 2017 and 2016 , respectively. The GSE Act requires us to set aside certain funding obligations, a portion of which is attributable to Treasury’s Capital Magnet Fund. In prior years, a portion was also attributable to Treasury’s HOPE Reserve Fund. In December 2014, FHFA directed us to set aside amounts for these contributions during each fiscal year, except for any fiscal year for which a draw from Treasury was made under the terms of the senior preferred stock purchase agreement, or in which such allocation or transfer would cause such a draw. Although we will draw funds from Treasury under the senior preferred stock purchase agreement to eliminate our fourth quarter 2017 net worth deficit, FHFA has directed us to proceed with the transfer of allocated funds for 2017 in light of FHFA’s determination that this draw is triggered by a one-time charge relating to the enactment of the Tax Cuts and Jobs Act (the “Tax Act”) and does not relate to any financial instability. These expenses, recognized in “Other expenses, net” in our consolidated statements of operations and comprehensive income, were measured as the product of 4.2 basis points and the unpaid principal balance of our total new business purchases for the respective period. We recognized $84 million in “Other expenses, net” in connection with Treasury’s Capital Magnet Fund for the year ended December 31, 2017 . We recognized $137 million and $111 million in “Other expenses, net” in connection with Treasury’s Capital Magnet and HOPE Reserve Funds for the years ended December 31, 2016 and 2015 , respectively. These amounts had not been remitted as of the end of the respective periods. In addition to the transactions with Treasury mentioned above, we purchase and sell Treasury securities in the normal course of business. As of December 31, 2017 and 2016 , we held Treasury securities with a fair value of $29.2 billion and $32.3 billion , respectively, and accrued interest receivable of $77 million and $39 million , respectively. We recognized interest income on these securities held by us of $345 million , $157 million and $35 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. Transactions with Freddie Mac As of December 31, 2017 and 2016 , we held Freddie Mac mortgage-related securities with a fair value of $613 million and $1.4 billion , respectively, and accrued interest receivable of $2 million and $5 million , respectively. We recognized interest income on these securities held by us of $38 million , $112 million and $226 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. Freddie Mac may be an investor in variable interest entities (“VIEs”) that we have consolidated, and we may be an investor in VIEs that Freddie Mac has consolidated. Freddie Mac may also be an investor in our debt securities. Transactions with FHFA The GSE Act authorizes FHFA to establish an annual assessment for regulated entities, including Fannie Mae, which is payable on a semi-annual basis (April and October), for FHFA’s costs and expenses, as well as to maintain FHFA’s working capital. We recognized FHFA assessment fees, which are recorded in “Administrative expenses” in our consolidated statements of operations and comprehensive income, of $112 million , $114 million and $112 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. Transactions with CSS In connection with our jointly owned company with Freddie Mac, we contributed capital to CSS of $102 million , $118 million and $66 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. In November 2016, Fannie Mae, Freddie Mac and CSS entered into a Customer Services Agreement that sets forth the terms under which CSS will provide securitization services to us and Freddie Mac. No other transactions outside of normal business activities have occurred between us and Freddie Mac during the years ended December 31, 2017 , 2016 or 2015 . Use of Estimates Preparing consolidated financial statements in accordance with GAAP requires management to make estimates and assumptions that affect our reported amounts of assets and liabilities, and disclosure of contingent assets and liabilities as of the dates of our consolidated financial statements, as well as our reported amounts of revenues and expenses during the reporting periods. Management has made significant estimates in a variety of areas including, but not limited to, valuation of certain financial instruments, and allowance for loan losses. Actual results could be different from these estimates. In April 2012, FHFA issued Advisory Bulletin AB 2012-02, “Framework for Adversely Classifying Loans, Other Real Estate Owned, and Other Assets and Listing Assets for Special Mention” (the “Advisory Bulletin”), which prescribes, among other things, guidance on when a loan should be charged off. This change in estimate resulted in the recognition on January 1, 2015 of (1) $1.8 billion in charge-offs of held for investment loans, (2) $724 million in charge-offs of preforeclosure property taxes and insurance receivable and (3) a reduction to our allowance for loan losses and our allowance for preforeclosure property taxes and insurance receivable in amounts equal to charge-offs recognized in connection with held for investment loans and preforeclosure property taxes and insurance receivable. For the majority of our delinquent single-family loans, we charge off the loan at the date of foreclosure or other liquidation event (such as a deed-in-lieu of foreclosure or a short sale). For a subset of delinquent single-family loans, we charge off the portion of the loans that is deemed uncollectible prior to foreclosure when the loans have been delinquent for a specified length of time and meet specified mark-to-market loan-to-value (“LTV”) ratios. We continue to enhance our data collection and analysis efforts to further refine our loss estimates as we obtain incremental information on the performance of our loans. Principles of Consolidation Our consolidated financial statements include our accounts as well as the accounts of the other entities in which we have a controlling financial interest. All intercompany balances and transactions have been eliminated. The typical condition for a controlling financial interest is ownership of a majority of the voting interests of an entity. A controlling financial interest may also exist in entities through arrangements that do not involve voting interests, such as a VIE. VIE Assessment We have interests in various entities that are considered VIEs. A VIE is an entity (1) that has total equity at risk that is not sufficient to finance its activities without additional subordinated financial support from other entities, (2) where the group of equity holders does not have the power to direct the activities of the entity that most significantly impact the entity’s economic performance, or the obligation to absorb the entity’s expected losses or the right to receive the entity’s expected residual returns, or both, or (3) where the voting rights of some investors are not proportional to their obligations to absorb the expected losses of the entity, their rights to receive the expected residual returns of the entity, or both, and substantially all of the entity’s activities either involve or are conducted on behalf of an investor that has disproportionately few voting rights. We determine if an entity is a VIE by performing a qualitative analysis, which requires certain subjective decisions including, but not limited to, the design of the entity, the variability that the entity was designed to create and pass along to its interest holders, the rights of the parties and the purpose of the arrangement. If we cannot conclude after a qualitative analysis whether an entity is a VIE, we perform a quantitative analysis. The primary types of VIE entities with which we are involved are securitization trusts guaranteed by us via lender swap and portfolio securitization transactions, limited partnership investments in low-income housing tax credit (“LIHTC”) and other housing partnerships, as well as mortgage and asset-backed trusts that were not created by us. Primary Beneficiary Determination If an entity is a VIE, we consider whether our variable interest in that entity causes us to be the primary beneficiary. We are deemed to be the primary beneficiary of a VIE when we have both (1) the power to direct the activities of the VIE that most significantly impact the entity’s economic performance, and (2) exposure to benefits and/or losses that could potentially be significant to the entity. The primary beneficiary of the VIE is required to consolidate and account for the assets, liabilities, and noncontrolling interests of the VIE in its consolidated financial statements. The assessment of which party has the power to direct the activities of the VIE may require significant management judgment when (1) more than one party has power or (2) more than one party is involved in the design of the VIE but no party has the power to direct the ongoing activities that could be significant. We continually assess whether we are the primary beneficiary of the VIEs with which we are involved and therefore may consolidate or deconsolidate a VIE through the duration of our involvement. Examples of certain events that may change whether or not we consolidate the VIE include a change in the design of the entity or a change in our ownership in the entity such that we no longer hold substantially all of the certificates issued by a multi-class resecuritization trust. Measurement of Consolidated Assets and Liabilities When we are the transferor of assets into a VIE that we consolidate at the time of the transfer, we continue to recognize the assets and liabilities of the VIE at the amounts that they would have been recognized if we had not transferred them, and no gain or loss is recognized. For all other VIEs that we consolidate (that is, those for which we are not the transferor), we recognize the assets and liabilities of the VIE in our consolidated financial statements at fair value, and we recognize a gain or loss for the difference between (1) the fair value of the consideration paid, fair value of noncontrolling interests and the reported amount of any previously held interests, and (2) the net amount of the fair value of the assets and liabilities consolidated. However, for the securitization trusts established under our lender swap program, no gain or loss is recognized if the trust is consolidated at formation as there is no difference in the respective fair value of (1) and (2) above. We record gains or losses that are associated with the consolidation of VIEs as a component of “Investment gains, net” in our consolidated statements of operations and comprehensive income . If we cease to be deemed the primary beneficiary of a VIE, we deconsolidate the VIE. We use fair value to measure the initial cost basis for any retained interests that are recorded upon the deconsolidation of a VIE. Any difference between the fair value and the previous carrying amount of our investment in the VIE is recorded as “Investment gains, net” in our consolidated statements of operations and comprehensive income. Purchase/Sale of Fannie Mae Securities We actively purchase and may subsequently sell guaranteed MBS that have been issued through lender swap and portfolio securitization transactions. The accounting for the purchase and sale of our guaranteed MBS issued by the trusts differs based on the characteristics of the securitization trusts and whether the trusts are consolidated. Single-Class Securitization Trusts We create single-class securitization trusts to issue single-class Fannie Mae MBS that evidence an undivided interest in the mortgage loans held in the trust. Investors in single-class Fannie Mae MBS receive principal and interest payments in proportion to their percentage ownership of the MBS issuance. We guarantee to each single-class securitization trust that we will supplement amounts received by the single-class securitization trust as required to permit timely payments of principal and interest on the related Fannie Mae MBS. This guaranty exposes us to credit losses on the loans underlying Fannie Mae MBS. Single-class securitization trusts are used for lender swap and portfolio securitization transactions. A lender swap transaction occurs when a mortgage lender delivers a pool of single-family mortgage loans to us, which we immediately deposit into an MBS trust. The MBS are then issued to the lender in exchange for the mortgage loans. A portfolio securitization transaction occurs when we purchase mortgage loans from third-party sellers for cash and later deposit these loans into an MBS trust. The securities issued through a portfolio securitization are then sold to investors for cash. We consolidate single-class securitization trusts that are issued under these programs when our role as guarantor and master servicer provides us with the power to direct matters, such as the servicing of the mortgage loans, that impact the credit risk to which we are exposed. In contrast, we do not consolidate single-class securitization trusts when other organizations have the power to direct these activities ( e.g ., when the loan collateral is subject to a Federal Housing Administration guaranty and related Servicing Guide). When we purchase single-class Fannie Mae MBS issued from a consolidated trust, we account for the transaction as an extinguishment of the related debt in our consolidated financial statements. We record a gain or loss on the extinguishment of such debt to the extent that the purchase price of the MBS does not equal the carrying value of the related consolidated debt reported in our consolidated balance sheets (including unamortized premiums, discounts or the other cost basis adjustments) at the time of purchase. When we sell single-class Fannie Mae MBS that were issued from a consolidated trust, we account for the transaction as the issuance of debt in our consolidated financial statements. We amortize the related premiums, discounts and other cost basis adjustments into income over time. If a single-class securitization trust is not consolidated, we account for the purchase and subsequent sale of such securities as the transfer of an investment security in accordance with the accounting guidance for transfers of financial assets. Single-Class Resecuritization Trusts Single-class resecuritization trusts (Fannie Megas ® ) are created by depositing Fannie Mae MBS into a new securitization trust for the purpose of aggregating multiple MBS into a single larger security. The cash flows from the new security represent an aggregation of the cash flows from the underlying MBS. We guarantee to each single-class resecuritization trust that we will supplement amounts received by the trust as required to permit timely payments of principal and interest on the related Fannie Mae securities. However, we assume no additional credit risk in such a resecuritization transaction, because the underlying assets are MBS for which we have already provided a guaranty. Additionally, our involvement with these trusts does not provide any incremental rights or power that would enable Fannie Mae to direct any activities of the trusts. As a result, we have concluded that we are not the primary beneficiaries of, and therefore do not consolidate, our single-class resecuritization trusts. As our single-class resecuritization securities pass through all of the cash flows of the underlying MBS directly to the holders of the securities, they are deemed to be substantially the same as the underlying MBS. Therefore, we account for purchases of our single-class resecuritization securities as an extinguishment of the underlying MBS debt

Consolidations and Transfers of

Consolidations and Transfers of Financial Assets	12 Months Ended
	Dec. 31, 2017
Consolidations and Transfers of Financial Assets [Abstract]
Consolidations and Transfers of Financial Assets	Consolidations and Transfers of Financial Assets We have interests in various entities that are considered to be VIEs. The primary types of entities are securitization trusts guaranteed by us via lender swap and portfolio securitization transactions and mortgage-backed trusts that were not created by us, as well as housing partnerships that are established to finance the acquisition, construction, development or rehabilitation of affordable multifamily and single-family housing. These interests include investments in securities issued by VIEs, such as Fannie Mae MBS created pursuant to our securitization transactions and our guaranty to the entity. We consolidate the substantial majority of our single-class securitization trusts because our role as guarantor and master servicer provides us with the power to direct matters (primarily the servicing of mortgage loans) that impact the credit risk to which we are exposed. In contrast, we do not consolidate single-class securitization trusts when other organizations have the power to direct these activities. Types of VIEs Securitization Trusts Under our lender swap and portfolio securitization transactions, mortgage loans are transferred to a trust specifically for the purpose of issuing a single class of guaranteed securities that are collateralized by the underlying mortgage loans. The trust’s permitted activities include receiving the transferred assets, issuing beneficial interests, establishing the guaranty and servicing the underlying mortgage loans. In our capacity as issuer, master servicer, trustee and guarantor, we earn fees for our obligations to each trust. Additionally, we may retain or purchase a portion of the securities issued by each trust. We have securitized mortgage loans since 1981. In our structured securitization transactions, we earn fees for assisting lenders and dealers with the design and issuance of structured mortgage-related securities. The trusts created in these transactions have permitted activities that are similar to those for our lender swap and portfolio securitization transactions. The assets of these trusts may include mortgage-related securities and/or mortgage loans. The trusts created for Fannie Megas issue single-class securities while the trusts created for REMIC, grantor trust and stripped mortgage-backed securities (“SMBS”) issue single-class and multi-class securities, the latter of which separate the cash flows from underlying assets into separately tradable interests. Our obligations and continued involvement in these trusts are similar to those described for lender swap and portfolio securitization transactions. We have securitized mortgage assets in structured transactions since 1986. We also invest in mortgage-backed securities that have been issued via private-label trusts. These trusts are structured to provide investors with a beneficial interest in a pool of receivables or other financial assets, typically mortgage loans. The trusts act as vehicles to allow loan originators to securitize assets. Securities are structured from the underlying pool of assets to provide for varying degrees of risk. The originators of the financial assets or the underwriters of the transaction create the trusts and typically own the residual interest in the trusts’ assets. Our involvement in these entities is typically limited to our recorded investment in the beneficial interests that we have purchased. We have invested in these vehicles since 1987. Limited Partnerships We have historically made equity investments in various limited partnerships that sponsor affordable housing projects utilizing the low-income housing tax credit pursuant to Section 42 of the Internal Revenue Code. The purpose of these investments is to increase the supply of affordable housing in the United States and to serve communities in need. In addition, our investments in LIHTC partnerships generate both tax credits and net operating losses that may reduce our federal income tax liability. Our LIHTC investments primarily represent limited partnership interests in entities that have been organized by a fund manager who acts as the general partner. These fund investments seek out equity investments in LIHTC operating partnerships that have been established to identify, develop and operate multifamily housing that is leased to qualifying residential tenants. We no longer recognize net operating losses or impairment on our LIHTC partnership investments as the carrying value is zero . We did not make any LIHTC investments in 2017 , 2016 or 2015 , other than pursuant to existing prior commitments. Consolidated VIEs If an entity is a VIE, we consider whether our variable interest in that entity causes us to be the primary beneficiary. The primary beneficiary of the VIE is required to consolidate and account for the assets, liabilities and noncontrolling interests of the VIE in its consolidated financial statements. An enterprise is deemed to be the primary beneficiary when the enterprise has the power to direct the activities of the VIE that most significantly impact the entity’s economic performance and exposure to benefits and/or losses could potentially be significant to the entity. In general, the investors in the obligations of consolidated VIEs have recourse only to the assets of those VIEs and do not have recourse to us, except where we provide a guaranty to the VIE. We continually assess whether we are the primary beneficiary of the VIEs with which we are involved and therefore may consolidate or deconsolidate a VIE through the duration of our involvement. As of December 31, 2017 , we consolidated certain VIEs that were not consolidated as of December 31, 2016 . As a result of consolidating these entities, which had combined total assets of $17 million in unpaid principal balance as of December 31, 2017 , we derecognized our investment in these entities and recognized the assets and liabilities of the consolidated entities at fair value. As of December 31, 2017 , we also deconsolidated certain VIEs that were consolidated and had combined total assets of $258 million in unpaid principal balance as of December 31, 2016 . The majority of this activity related to the deconsolidation of multi-class resecuritization trusts containing consolidated Fannie Mae MBS, which resulted in the recognition of the debt issued to third parties of the MBS trusts we consolidated and the fair value of our retained interests as securities in our consolidated balance sheets. Unconsolidated VIEs We do not consolidate VIEs when we are not deemed to be the primary beneficiary. Our unconsolidated VIEs include securitization trusts and limited partnerships. The following table displays the carrying amount and classification of our assets and liabilities that relate to our involvement with unconsolidated mortgage-backed trusts. As of December 31, 2017 2016 (Dollars in millions) Assets and liabilities recorded in our consolidated balance sheets related to mortgage-backed trusts: Assets: Trading securities: Fannie Mae $ 3,809 $ 4,642 Non-Fannie Mae 1,580 3,473 Total trading securities 5,389 8,115 Available-for-sale securities: Fannie Mae 2,032 2,447 Non-Fannie Mae 2,062 4,879 Total available-for-sale securities 4,094 7,326 Other assets 74 77 Other liabilities (467 ) (528 ) Net carrying amount $ 9,090 $ 14,990 Our maximum exposure to loss generally represents the greater of our recorded investment in the entity or the unpaid principal balance of the assets covered by our guaranty. However, our securities issued by Fannie Mae multi-class resecuritization trusts that are not consolidated do not give rise to any additional exposure to loss as we already consolidate the underlying collateral. The maximum exposure to loss related to unconsolidated mortgage-backed trusts was approximately $15 billion and $21 billion as of December 31, 2017 and 2016 , respectively. The total assets of our unconsolidated mortgage-backed trusts were approximately $70 billion and $150 billion as of December 31, 2017 and 2016 , respectively. The maximum exposure to loss for our unconsolidated limited partnerships and similar legal entities, which consist of LIHTC investments, community investments and other entities, was $105 million and the related carrying value was $82 million as of December 31, 2017 . As of December 31, 2016 , the maximum exposure to loss was $118 million and the related carrying value was $92 million . The total assets of these limited partnership investments were $3.2 billion and $3.9 billion as of December 31, 2017 and 2016 , respectively. The unpaid principal balance of our multifamily loan portfolio wa s $265.1 billion as of December 31, 2017 . As our lending relationship does not provide us with a controlling financial interest in the borrower entity, we do not consolidate these borrowers regardless of their status as either a VIE or a voting interest entity. We have excluded these entities from our VIE disclosures. However, the disclosures we have provided in “ Note 3, Mortgage Loans ,” “ Note 4, Allowance for Loan Losses ” and “ Note 6, Financial Guarantees ” with respect to this population are consistent with the FASB’s stated objectives for the disclosures related to unconsolidated VIEs. Transfers of Financial Assets We issue Fannie Mae MBS through portfolio securitization transactions by transferring pools of mortgage loans or mortgage-related securities to one or more trusts or special purpose entities. We are considered to be the transferor when we transfer assets from our own retained mortgage portfolio in a portfolio securitization transaction. For the years ended December 31, 2017 , 2016 and 2015 , the unpaid principal balance of portfolio securitizations was $252.7 billion , $264.7 billion and $212.0 billion , respectively. We retain interests from the transfer and sale of mortgage-related securities to unconsolidated single-class and multi-class portfolio securitization trusts. As of December 31, 2017 , the unpaid principal balance of retained interests was $3.9 billion and its related fair value was $4.7 billion . The unpaid principal balance of retained interests was $4.4 billion and its related fair value was $5.8 billion as of December 31, 2016 . For the years ended December 31, 2017 , 2016 and 2015 , the principal and interest received on retained interests was $1.1 billion , $1.2 billion and $1.2 billion , respectively. Managed Loans Managed loans are on-balance sheet mortgage loans, as well as mortgage loans that we have securitized in unconsolidated portfolio securitization trusts. The unpaid principal balance of securitized loans in unconsolidated portfolio securitization trusts, which are primarily loans that are guaranteed or insured, in whole or in part, by the U.S. government, was $1.3 billion and $1.4 billion as of December 31, 2017 and 2016 , respectively. For information on our on-balance sheet mortgage loans, see “ Note 3, Mortgage Loans .”

Mortgage Loans

Mortgage Loans	12 Months Ended
	Dec. 31, 2017
Mortgage Loans on Real Estate [Abstract]
Mortgage Loans	Mortgage Loans We own single-family mortgage loans, which are secured by four or fewer residential dwelling units, and multifamily mortgage loans, which are secured by five or more residential dwelling units. We classify these loans as either HFI or HFS. We report the carrying value of HFI loans at the unpaid principal balance, net of unamortized premiums and discounts, other cost basis adjustments, and an allowance for loan losses. We report the carrying value of HFS loans at the lower of cost or fair value and record valuation changes in “Investment gains, net” in our consolidated statements of operations and comprehensive income. We define the recorded investment of HFI loans as unpaid principal balance, net of unamortized premiums and discounts, other cost basis adjustments, and accrued interest receivable. For purposes of the single-family mortgage loan disclosures below, we define “primary” class as mortgage loans that are not included in other loan classes; “government” class as mortgage loans that are guaranteed or insured, in whole or in part, by the U.S. government or one of its agencies, and that are not Alt-A; and “other” class as loans with higher-risk characteristics, such as interest-only loans and negative-amortizing loans, that are neither government nor Alt-A. The following table displays the carrying value of our mortgage loans. As of December 31, 2017 2016 (Dollars in millions) Single-family $ 2,890,634 $ 2,833,750 Multifamily 265,069 229,896 Total unpaid principal balance of mortgage loans 3,155,703 3,063,646 Cost basis and fair value adjustments, net 41,906 39,572 Allowance for loan losses for loans held for investment (19,084 ) (23,465 ) Total mortgage loans $ 3,178,525 $ 3,079,753 For the years ended December 31, 2017 , 2016 and 2015 , we redesignated loans with a carrying value of $12.9 billion , $3.9 billion and $8.6 billion , respectively, from HFI to HFS. For the year ended December 31, 2017 , we redesignated loans with a carrying value of $113 million from HFS to HFI. We sold loans with an unpaid principal balance of $12.2 billion , $6.7 billion and $3.6 billion , respectively, during the years ended December 31, 2017 , 2016 and 2015 . The realized gains on the sales of mortgage loans were $723 million , $54 million and $274 million as of December 31, 2017 , 2016 and 2015 , respectively. The recorded investment of single-family mortgage loans for which formal foreclosure proceedings are in process was $13.0 billion and $18.3 billion as of December 31, 2017 and 2016 , respectively. As a result of our various loss mitigation and foreclosure prevention efforts, we expect that a portion of the loans in the process of formal foreclosure proceedings will not ultimately foreclose. Aging Analysis The following tables display an aging analysis of the total recorded investment in our HFI mortgage loans by portfolio segment and class, excluding loans for which we have elected the fair value option. As of December 31, 2017 30 - 59 Days Delinquent 60 - 89 Days Delinquent Seriously Delinquent (1) Total Delinquent Current Total Recorded Investment in Loans 90 Days or More Delinquent and Accruing Interest Recorded Investment in Nonaccrual Loans (Dollars in millions) Single-family: Primary $ 35,582 $ 10,396 $ 23,999 $ 69,977 $ 2,732,818 $ 2,802,795 $ 87 $ 37,971 Government (2) 55 21 206 282 30,807 31,089 206 — Alt-A 3,186 1,147 3,418 7,751 59,475 67,226 5 5,094 Other 1,185 411 1,252 2,848 19,016 21,864 5 1,834 Total single-family 40,008 11,975 28,875 80,858 2,842,116 2,922,974 303 44,899 Multifamily (3) 26 N/A 276 302 266,699 267,001 — 424 Total $ 40,034 $ 11,975 $ 29,151 $ 81,160 $ 3,108,815 $ 3,189,975 $ 303 $ 45,323 As of December 31, 2016 30 - 59 Days Delinquent 60 - 89 Days Delinquent Seriously Delinquent (1) Total Delinquent Current Total Recorded Investment in Loans 90 Days or More Delinquent and Accruing Interest Recorded Investment in Nonaccrual Loans (Dollars in millions) Single-family: Primary $ 31,631 $ 7,910 $ 21,761 $ 61,302 $ 2,654,195 $ 2,715,497 $ 22 $ 33,448 Government (2) 56 22 256 334 36,814 37,148 256 — Alt-A 3,629 1,194 4,221 9,044 72,903 81,947 2 6,019 Other 1,349 438 1,582 3,369 25,974 29,343 5 2,238 Total single-family 36,665 9,564 27,820 74,049 2,789,886 2,863,935 285 41,705 Multifamily (3) 44 N/A 129 173 231,708 231,881 — 403 Total $ 36,709 $ 9,564 $ 27,949 $ 74,222 $ 3,021,594 $ 3,095,816 $ 285 $ 42,108 __________ (1) Single-family seriously delinquent loans are loans that are 90 days or more past due or in the foreclosure process. Multifamily seriously delinquent loans are loans that are 60 days or more past due. (2) Primarily consists of reverse mortgages, which due to their nature, are not aged and are included in the current column. (3) Multifamily loans 60 - 89 days delinquent are included in the seriously delinquent column. Credit Quality Indicators The following table displays the total recorded investment in our single-family HFI loans by class and credit quality indicator, excluding loans for which we have elected the fair value option. As of December 31, 2017 (1) 2016 (1) Primary Alt-A Other Primary Alt-A Other (Dollars in millions) Estimated mark-to-market LTV ratio: (2) Less than or equal to 80% $ 2,439,858 $ 51,903 $ 16,428 $ 2,321,201 $ 56,250 $ 19,382 Greater than 80% and less than or equal to 90% 238,038 6,680 2,277 244,231 9,787 3,657 Greater than 90% and less than or equal to 100% 106,076 4,044 1,443 114,412 6,731 2,627 Greater than 100% 18,823 4,599 1,716 35,653 9,179 3,677 Total $ 2,802,795 $ 67,226 $ 21,864 $ 2,715,497 $ 81,947 $ 29,343 __________ (1) Excludes $31.1 billion and $37.1 billion as of December 31, 2017 and 2016 , respectively, of mortgage loans guaranteed or insured, in whole or in part, by the U.S. government or one of its agencies, that are not Alt-A loans. The segment class is primarily reverse mortgages for which we do not calculate an estimated mark-to-market LTV ratio. (2) The aggregate estimated mark-to-market LTV ratio is based on the unpaid principal balance of the loan as of the end of each reported period divided by the estimated current value of the property, which we calculate using an internal valuation model that estimates periodic changes in home value. The following table displays the total recorded investment in our multifamily HFI loans by credit quality indicator, excluding loans for which we have elected the fair value option. As of December 31, 2017 2016 (Dollars in millions) Credit risk profile by internally assigned grade: Non-classified $ 263,416 $ 228,749 Classified: (1) Substandard 3,585 3,129 Doubtful — 3 Total classified 3,585 3,132 Total $ 267,001 $ 231,881 __________ (1) A loan classified as “Substandard” has a well-defined weakness that jeopardizes the timely full repayment. “Doubtful” refers to a loan with a weakness that makes collection or liquidation in full highly questionable and improbable based on existing conditions and values. Individually Impaired Loans Individually impaired loans include TDRs, acquired credit-impaired loans and multifamily loans that we have assessed as probable that we will not collect all contractual amounts due, regardless of whether we are currently accruing interest, excluding loans classified as HFS. The following tables display the total unpaid principal balance, recorded investment, related allowance, average recorded investment and interest income recognized for individually impaired loans. As of December 31, 2017 2016 Unpaid Principal Balance Total Recorded Investment Related Allowance for Loan Losses Unpaid Principal Balance Total Recorded Investment Related Allowance for Loan Losses (Dollars in millions) Individually impaired loans: With related allowance recorded: Single-family: Primary $ 91,194 $ 86,864 $ (11,652 ) $ 105,113 $ 99,825 $ (14,462 ) Government 276 279 (56 ) 302 305 (59 ) Alt-A 23,077 21,045 (4,046 ) 28,599 26,059 (5,365 ) Other 8,488 8,006 (1,493 ) 11,087 10,465 (2,034 ) Total single-family 123,035 116,194 (17,247 ) 145,101 136,654 (21,920 ) Multifamily 279 280 (42 ) 320 323 (33 ) Total individually impaired loans with related allowance recorded 123,314 116,474 (17,289 ) 145,421 136,977 (21,953 ) With no related allowance recorded: (1) Single-family: Primary 16,027 15,158 — 15,733 14,758 — Government 66 60 — 63 59 — Alt-A 3,253 2,870 — 3,511 3,062 — Other 988 909 — 1,159 1,065 — Total single-family 20,334 18,997 — 20,466 18,944 — Multifamily 308 310 — 266 266 — Total individually impaired loans with no related allowance recorded 20,642 19,307 — 20,732 19,210 — Total individually impaired loans (2) $ 143,956 $ 135,781 $ (17,289 ) $ 166,153 $ 156,187 $ (21,953 ) For the Year Ended December 31, 2017 2016 2015 Average Recorded Investment Total Interest Income Recognized (3) Interest Income Recognized on a Cash Basis Average Recorded Investment Total Interest Income Recognized (3) Interest Income Recognized on a Cash Basis Average Recorded Investment Total Interest Income Recognized (3) Interest Income Recognized on a Cash Basis (Dollars in millions) Individually impaired loans: With related allowance recorded: Single-family: Primary $ 92,893 $ 3,721 $ 319 $ 105,076 $ 4,004 $ 325 $ 114,737 $ 4,190 $ 318 Government 292 10 — 314 12 — 299 12 — Alt-A 23,536 929 56 27,512 1,010 54 30,453 1,034 54 Other 9,158 318 19 11,382 365 20 12,863 376 21 Total single-family 125,879 4,978 394 144,284 5,391 399 158,352 5,612 393 Multifamily 273 9 — 508 29 — 973 16 — Total individually impaired loans with related allowance recorded 126,152 4,987 394 144,792 5,420 399 159,325 5,628 393 With no related allowance recorded: (1) Single-family: Primary 15,166 1,107 96 15,293 1,236 91 15,796 1,039 91 Government 61 3 — 59 4 — 55 4 — Alt-A 3,000 270 13 3,293 309 9 3,647 218 11 Other 997 84 4 1,116 108 3 1,259 75 3 Total single-family 19,224 1,464 113 19,761 1,657 103 20,757 1,336 105 Multifamily 297 19 — 317 13 — 442 10 — Total individually impaired loans with no related allowance recorded 19,521 1,483 113 20,078 1,670 103 21,199 1,346 105 Total individually impaired loans $ 145,673 $ 6,470 $ 507 $ 164,870 $ 7,090 $ 502 $ 180,524 $ 6,974 $ 498 __________ (1) The discounted cash flows or collateral value equals or exceeds the carrying value of the loan and, as such, no valuation allowance is required. (2) Includes single-family loans restructured in a TDR with a recorded investment of $134.7 billion and $155.0 billion as of December 31, 2017 and 2016 , respectively. Includes multifamily loans restructured in a TDR with a recorded investment of $185 million and $248 million as of December 31, 2017 and 2016 , respectively. (3) Total single-family interest income recognized of $6.4 billion for the year ended December 31, 2017 consists of $5.5 billion of contractual interest and $925 million of effective yield adjustments. Total single-family interest income recognized of $7.0 billion for the year ended December 31, 2016 consists of $5.7 billion of contractual interest and $1.3 billion of effective yield adjustments. Total single-family interest income recognized of $6.9 billion for the year ended December 31, 2015 consists of $5.7 billion of contractual interest and $1.2 billion of effective yield adjustments. Troubled Debt Restructurings A modification to the contractual terms of a loan that results in granting a concession to a borrower experiencing financial difficulties is considered a TDR. In addition to formal loan modifications, we also engage in other loss mitigation activities with troubled borrowers, which include repayment plans and forbearance arrangements, both of which represent informal agreements with the borrower that do not result in the legal modification of the loan’s contractual terms. We account for these informal restructurings as a TDR if we defer more than three missed payments. We also classify loans to certain borrowers who have received bankruptcy relief as TDRs. The substantial majority of the loan modifications we complete result in term extensions, interest rate reductions or a combination of both. The average term extension of a single-family modified loan was 153 months , 157 months and 161 months for the years ended December 31, 2017 , 2016 and 2015 , respectively. The average interest rate reduction was 0.56 , 0.79 and 0.74 percentage points for the years ended December 31, 2017 , 2016 and 2015 , respectively. The following table displays the number of loans and recorded investment in loans restructured in a TDR. For the Year Ended December 31, 2017 2016 2015 Number of Loans Recorded Investment Number of Loans Recorded Investment Number of Loans Recorded Investment (Dollars in millions) Single-family: Primary 59,708 $ 8,247 61,586 $ 8,405 71,293 $ 9,713 Government 171 18 186 20 241 27 Alt-A 5,369 771 6,647 946 9,037 1,374 Other 1,158 207 1,381 244 1,835 333 Total single-family 66,406 9,243 69,800 9,615 82,406 11,447 Multifamily 8 99 11 66 12 40 Total TDRs 66,414 $ 9,342 69,811 $ 9,681 82,418 $ 11,487 The following table displays the number of loans and our recorded investment in these loans at the time of payment default for loans that were restructured in a TDR in the twelve months prior to the payment default. For purposes of this disclosure, we define loans that had a payment default as: single-family and multifamily loans with completed TDRs that liquidated during the period, either through foreclosure, deed-in-lieu of foreclosure or a short sale; single-family loans with completed modifications that are two or more months delinquent during the period; or multifamily loans with completed modifications that are one or more months delinquent during the period. For the Year Ended December 31, 2017 2016 2015 Number of Loans Recorded Investment Number of Loans Recorded Investment Number of Loans Recorded Investment (Dollars in millions) Single-family: Primary 19,539 $ 2,722 20,810 $ 2,938 26,206 $ 3,808 Government 91 10 95 11 118 16 Alt-A 2,588 400 3,131 500 4,128 706 Other 760 145 1,002 172 1,229 247 Total single-family 22,978 3,277 25,038 3,621 31,681 4,777 Multifamily 2 12 5 46 3 6 Total TDRs that subsequently defaulted 22,980 $ 3,289 25,043 $ 3,667 31,684 $ 4,783

Allowance for Loan Losses

Allowance for Loan Losses	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Allowance for Loan Losses	Allowance for Loan Losses We maintain an allowance for loan losses for HFI loans held by Fannie Mae and loans backing Fannie Mae MBS issued from consolidated trusts. When calculating our allowance for loan losses, we consider the unpaid principal balance, net of amortized premiums and discounts, and other cost basis adjustments of HFI loans at the balance sheet date. The following table displays changes in single-family, multifamily and total allowance for loan losses. As of December 31, 2017 2016 2015 (Dollars in millions) Single-family allowance for loan losses: Beginning balance $ (23,283 ) $ (27,709 ) $ (35,177 ) Benefit for loan losses (1) 1,994 1,704 68 Charge-offs (2) 2,795 3,254 9,731 Recoveries (326 ) (442 ) (1,136 ) Other (3) (29 ) (90 ) (1,195 ) Ending balance $ (18,849 ) $ (23,283 ) $ (27,709 ) Multifamily allowance for loan losses: Beginning balance $ (182 ) $ (242 ) $ (364 ) Benefit (provision) for loan losses (1) (53 ) 55 90 Charge-offs (2) 3 12 43 Recoveries (3 ) (7 ) (4 ) Other (3) — — (7 ) Ending balance $ (235 ) $ (182 ) $ (242 ) Total allowance for loan losses: Beginning balance $ (23,465 ) $ (27,951 ) $ (35,541 ) Benefit for loan losses (1) 1,941 1,759 158 Charge-offs (2) 2,798 3,266 9,774 Recoveries (329 ) (449 ) (1,140 ) Other (3) (29 ) (90 ) (1,202 ) Ending balance $ (19,084 ) $ (23,465 ) $ (27,951 ) __________ (1) Benefit (provision) for loan losses is included in “ Benefit for credit losses ” in our consolidated statements of operations and comprehensive income. (2) For the year ended December 31, 2015, includes charge-offs of (1) $1.8 billion in loans held for investment and $724 million in preforeclosure property taxes and insurance receivable in connection with our adoption of the Advisory Bulletin on January 1, 2015 and (2) $1.1 billion in accrued interest receivable in connection with our adoption of a change in accounting policy on January 1, 2015 related to the treatment of interest previously accrued, but not collected, at the date that loans are placed on nonaccrual status. (3) Amounts represent changes in other loss reserves which are reflected in benefit (provision) for loan losses, charge-offs, and recoveries. As of December 31, 2017, we included an estimate of incurred credit losses from Hurricanes Harvey, Irma and Maria (collectively, the “hurricanes”) of approximately $900 million in the allowance for loan losses. The following table displays the allowance for loan losses and recorded investment in our HFI loans by impairment or allowance methodology and portfolio segment, excluding loans for which we have elected the fair value option. As of December 31, 2017 2016 Single-Family Multifamily Total Single-Family Multifamily Total (Dollars in millions) Allowance for loan losses by segment: Individually impaired loans (1) $ (17,247 ) $ (42 ) $ (17,289 ) $ (21,920 ) $ (33 ) $ (21,953 ) Collectively reserved loans (1,602 ) (193 ) (1,795 ) (1,363 ) (149 ) (1,512 ) Total allowance for loan losses $ (18,849 ) $ (235 ) $ (19,084 ) $ (23,283 ) $ (182 ) $ (23,465 ) Recorded investment in loans by segment: Individually impaired loans (1) $ 135,191 $ 590 $ 135,781 $ 155,598 $ 589 $ 156,187 Collectively reserved loans 2,787,783 266,411 3,054,194 2,708,337 231,292 2,939,629 Total recorded investment in loans $ 2,922,974 $ 267,001 $ 3,189,975 $ 2,863,935 $ 231,881 $ 3,095,816 __________ (1) Includes acquired credit-impaired loans.

Investments in Securities

Investments in Securities	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Investments in Securities	Investments in Securities Trading Securities Trading securities are recorded at fair value with subsequent changes in fair value recorded as “ Fair value losses, net ” in our consolidated statements of operations and comprehensive income . The following table displays our investments in trading securities. As of December 31, 2017 2016 (Dollars in millions) Mortgage-related securities: Fannie Mae $ 3,876 $ 4,769 Other agency 1,118 2,058 Alt-A and subprime private-label securities 453 636 Commercial mortgage-backed securities (“CMBS”) 9 761 Mortgage revenue bonds 1 21 Total mortgage-related securities 5,457 8,245 U.S. Treasury securities 29,222 32,317 Total trading securities $ 34,679 $ 40,562 The following table displays information about our net trading gains and losses. For the Year Ended December 31, 2017 2016 2015 (Dollars in millions) Net trading gains (losses) $ 190 $ 28 $ (368 ) Net trading gains (losses) recognized in the period related to securities still held at period end 161 (19 ) (453 ) Available-for-Sale Securities We record AFS securities at fair value with unrealized gains and losses, recorded net of tax, as a component of “ Other comprehensive loss ” and we recognize realized gains and losses from the sale of AFS securities in “ Investment gains, net ” in our consolidated statements of operations and comprehensive income . The following table displays the gross realized gains, losses and proceeds on sales of AFS securities. For the Year Ended December 31, 2017 2016 2015 (Dollars in millions) Gross realized gains $ 487 $ 1,043 $ 1,066 Gross realized losses 1 17 70 Total proceeds (excludes initial sale of securities from new portfolio securitizations) 1,780 10,993 8,023 The following tables display the amortized cost, gross unrealized gains and losses, and fair value by major security type for AFS securities. As of December 31, 2017 Total Amortized Cost (1) Gross Unrealized Gains Gross Unrealized Losses (2) Total Fair Value (Dollars in millions) Fannie Mae $ 2,044 $ 102 $ (27 ) $ 2,119 Other agency 332 25 — 357 Alt-A and subprime private-label securities 662 652 — 1,314 CMBS 15 — — 15 Mortgage revenue bonds 655 20 (4 ) 671 Other mortgage-related securities 350 17 — 367 Total $ 4,058 $ 816 $ (31 ) $ 4,843 As of December 31, 2016 Total Amortized Cost (1) Gross Unrealized Gains Gross Unrealized Losses (2) Total Fair Value (Dollars in millions) Fannie Mae $ 2,445 $ 137 $ (28 ) $ 2,554 Other agency 508 39 — 547 Alt-A and subprime private-label securities 1,817 895 (3 ) 2,709 CMBS 815 4 — 819 Mortgage revenue bonds 1,245 36 (9 ) 1,272 Other mortgage-related securities 431 31 — 462 Total $ 7,261 $ 1,142 $ (40 ) $ 8,363 s __________ (1) Amortized cost consists of unpaid principal balance, unamortized premiums, discounts and other cost basis adjustments, as well as OTTI recognized in “Investment gains, net” in our consolidated statements of operations and comprehensive income. (2) Represents the gross unrealized losses on securities for which we have not recognized OTTI, as well as the noncredit component of OTTI and cumulative changes in fair value of securities for which we previously recognized the credit component of OTTI in “Accumulated other comprehensive income” in our consolidated balance sheets. The following tables display additional information regarding gross unrealized losses and fair value by major security type for AFS securities in an unrealized loss position. As of December 31, 2017 Less Than 12 Consecutive Months 12 Consecutive Months or Longer Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value (Dollars in millions) Fannie Mae $ (1 ) $ 134 $ (26 ) $ 461 Mortgage revenue bonds — — (4 ) 3 Total $ (1 ) $ 134 $ (30 ) $ 464 As of December 31, 2016 Less Than 12 Consecutive Months 12 Consecutive Months or Longer Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value (Dollars in millions) Fannie Mae $ (2 ) $ 139 $ (26 ) $ 477 Alt-A and subprime private-label securities — — (3 ) 73 Mortgage revenue bonds (7 ) 78 (2 ) 6 Total $ (9 ) $ 217 $ (31 ) $ 556 Other-Than-Temporary Impairments For AFS securities, OTTI is considered to have occurred when the fair value of a debt security is below its amortized cost basis and we intend to sell or it is more likely than not that we will be required to sell the security before recovery. Additionally, OTTI is considered to have occurred if we do not expect to recover the entire amortized cost basis of a debt security even if we do not intend to sell the security or it is not more likely than not we will be required to sell the security before recovery. We recognized $ 5 million , $ 35 million and $ 196 million of OTTI for the years ended December 31, 2017 , 2016 and 2015 , respectively, which are included in “ Investment gains, net ” in consolidated statements of operations and comprehensive income . OTTI recognized for the year ended December 31, 2015 was higher than OTTI recognized for the years ended December 31, 2017 and 2016 primarily due to a change in our intent to sell certain securities during 2015 . As a result, we recognized the entire difference between the amortized cost basis of these securities and their fair value as OTTI. The balance of the unrealized credit loss component of AFS debt securities held by us and recognized in our consolidated statements of operations and comprehensive income was $1.1 billion , $1.9 billion and $2.4 billion as of December 31, 2017 , 2016 and 2015 , respectively. The decrease for the years ended 2017 and 2016 was primarily driven by securities we intend to sell or that it is more likely than not we will be required to sell before recovery of our amortized cost basis. Maturity Information The following table displays the amortized cost and fair value of our AFS securities by major security type and remaining contractual maturity, assuming no principal prepayments. The contractual maturity of mortgage-backed securities is not a reliable indicator of their expected life because borrowers generally have the right to prepay their obligations at any time. As of December 31, 2017 Total Amortized Cost Total Fair Value One Year or Less After One Year Through Five Years After Five Years Through Ten Years After Ten Years Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value (Dollars in millions) Fannie Mae $ 2,044 $ 2,119 $ 2 $ 2 $ 12 $ 12 $ 59 $ 63 $ 1,971 $ 2,042 Other agency 332 357 2 2 15 15 57 61 258 279 Alt-A and subprime private-label securities 662 1,314 — — — — — — 662 1,314 CMBS 15 15 15 15 — — — — — — Mortgage revenue bonds 655 671 15 15 75 75 83 85 482 496 Other mortgage-related securities 350 367 — — — — 5 5 345 362 Total $ 4,058 $ 4,843 $ 34 $ 34 $ 102 $ 102 $ 204 $ 214 $ 3,718 $ 4,493 Weighted average yield (1) 6.84 % 4.18 % 6.60 % 6.59 % 6.88 % __________ (1) Yields are determined by dividing interest income (including amortization and accretion of premiums, discounts and other cost basis adjustments) by amortized cost balances as of year-end. Yields on tax-exempt obligations have been computed on a tax equivalent basis.

Financial Guarantees

Financial Guarantees	12 Months Ended
	Dec. 31, 2017
Guarantees [Abstract]
Financial Guarantees	Financial Guarantees We generate revenue by absorbing the credit risk of mortgage loans in unconsolidated trusts in exchange for a guaranty fee. We also provide credit enhancements on taxable or tax-exempt mortgage revenue bonds issued by state and local governmental entities to finance multifamily housing for low- and moderate-income families. Additionally, we issue long-term standby commitments that generally require us to purchase loans from lenders if the loans meet certain delinquency criteria. We recognize a guaranty obligation for our obligation to stand ready to perform on our guarantees to unconsolidated trusts and other guaranty arrangements. These off-balance sheet guarantees expose us to credit losses primarily relating to the unpaid principal balance of our unconsolidated Fannie Mae MBS and other financial guarantees. The remaining contractual terms of our guarantees range from 5 days to 35 years; however, the actual term of each guaranty may be significantly less than the contractual term based on the prepayment characteristics of the related mortgage loans. The following table displays our off-balance sheet maximum exposure, guaranty obligation recognized in our consolidated balance sheets and the potential maximum recovery from third parties through available credit enhancements and recourse related to our financial guarantees. As of December 31, 2017 2016 Maximum Exposure Guaranty Obligation Maximum Recovery (1) Maximum Exposure Guaranty Obligation Maximum Recovery (1) (Dollars in millions) Unconsolidated Fannie Mae MBS $ 10,876 $ 127 $ 7,340 $ 12,607 $ 143 $ 8,048 Other guaranty arrangements (2) 14,265 131 2,404 15,335 137 2,663 Total $ 25,141 $ 258 $ 9,744 $ 27,942 $ 280 $ 10,711 __________ (1) Recoverability of such credit enhancements and recourse is subject to, among other factors, our mortgage insurers’ and financial guarantors’ ability to meet their obligations to us. For information on our mortgage insurers and financial guarantors, see “ Note 13, Concentrations of Credit Risk .” (2) Primarily consists of credit enhancements and long-term standby commitments.

Short-Term and Long-Term Debt

Short-Term and Long-Term Debt	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Short-Term and Long-Term Debt	Short-Term and Long-Term Debt Short-Term Debt The following table displays our outstanding short-term debt (borrowings with an original contractual maturity of one year or less) and weighted-average interest rates of these borrowings. As of December 31, 2017 2016 Outstanding Weighted- Average Interest Rate (1) Outstanding Weighted- Average Interest Rate (1) (Dollars in millions) Short-term debt of Fannie Mae $ 33,377 1.18 % $ 34,995 0.49 % Debt of consolidated trusts 379 1.11 584 0.48 Total short-term debt $ 33,756 1.18 % $ 35,579 0.49 % __________ (1) Includes the effects of discounts, premiums and other cost basis adjustments. Intraday Line of Credit We use a secured intraday funding line of credit provided by a large financial institution. We post collateral which, in some circumstances, the secured party has the right to repledge to third parties. As this line of credit is an uncommitted intraday loan facility, we may be unable to draw on it if and when needed. The line of credit under this facility was $15.0 billion as of December 31, 2017 and 2016 . Long-Term Debt Long-term debt represents borrowings with an original contractual maturity of greater than one year. The following table displays our outstanding long-term debt. As of December 31, 2017 2016 Maturities Outstanding Weighted- Average Interest Rate (1) Maturities Outstanding Weighted- Average Interest Rate (1) (Dollars in millions) Senior fixed: Benchmark notes and bonds 2018 - 2030 $ 123,541 2.11 % 2017 - 2030 $ 153,983 2.16 % Medium-term notes (2) 2018 - 2026 75,901 1.41 2017 - 2026 82,230 1.40 Other (3) 2018 - 2038 7,421 4.84 2017 - 2038 12,800 6.74 Total senior fixed 206,863 1.95 249,013 2.14 Senior floating: Medium-term notes (2) 2018 - 2020 8,425 1.36 2017 - 2019 21,476 0.71 Connecticut Avenue Securities (4) 2023 - 2030 22,527 5.18 2023 - 2029 16,511 4.77 Other (5) 2020 - 2037 376 6.36 2020 - 2037 346 6.75 Total senior floating 31,328 4.14 38,333 2.48 Subordinated debentures 2019 5,106 9.93 2019 4,645 9.93 Secured borrowings (6) 2021 - 2022 78 1.70 2021 - 2022 111 1.44 Total long-term debt of Fannie Mae (7) 243,375 2.40 292,102 2.31 Debt of consolidated trusts 2018 - 2057 3,052,923 2.80 2017 - 2056 2,934,635 2.57 Total long-term debt $ 3,296,298 2.77 % $ 3,226,737 2.54 % __________ (1) Includes the effects of discounts, premiums and other cost basis adjustments. (2) Includes long-term debt with an original contractual maturity of greater than 1 year and up to 10 years, excluding zero-coupon debt. (3) Includes other long-term debt with an original contractual maturity of greater than 10 years and foreign exchange bonds. (4) Credit risk-sharing securities that transfer a portion of the credit risk on specified pools of single-family mortgage loans to the investors in these securities, a portion of which is reported at fair value. (5) Consists of structured debt instruments that are reported at fair value. (6) Represents our remaining liability resulting from the transfer of financial assets from our consolidated balance sheets that did not qualify as a sale under the accounting guidance for the transfer of financial instruments. (7) Includes unamortized discounts and premiums, other cost basis adjustments and fair value adjustments of $752 million and $1.8 billion as of December 31, 2017 and 2016 , respectively. Our long-term debt includes a variety of debt types. We issue fixed and floating-rate medium-term notes with maturities greater than one year that are issued through dealer banks. We also offer Benchmark Notes in regularly-scheduled issuances that provide increased efficiency, liquidity and tradability to the market. Additionally, we have issued notes and bonds denominated in several foreign currencies. We effectively convert all foreign currency-denominated transactions into U.S. dollars through the use of foreign currency swaps for the purpose of funding our mortgage assets. Our long-term debt also includes Connecticut Avenue Securities (“CAS”), which are credit risk-sharing securities that transfer a portion of the credit risk on specified pools of mortgage loans to investors in these securities. Our other long-term debt includes callable and non-callable securities, which include all long-term non-Benchmark securities, such as zero-coupon bonds, fixed rate and other long-term securities, and are generally negotiated underwritings with one or more dealers or dealer banks. Characteristics of Debt As of December 31, 2017 and 2016 , the face amount of our debt securities of Fannie Mae was $277.5 billion and $328.9 billion , respectively. As of December 31, 2017 and 2016 , we had zero-coupon debt with a face amount of $39.8 billion and $45.9 billion , respectively, which had an effective interest rate of 2.29% and 2.43% , respectively. We issue callable debt instruments to manage the duration and prepayment risk of expected cash flows of the mortgage assets we own. Our outstanding debt as of December 31, 2017 and 2016 included $72.3 billion and $77.3 billion , respectively, of callable debt that could be redeemed in whole or in part at our option any time on or after a specified date. The following table displays the amount of our long-term debt as of December 31, 2017 by year of maturity for each of the years 2018 through 2022 and thereafter. The first column assumes that we pay off this debt at maturity or on the call date if the call has been announced, while the second column assumes that we redeem our callable debt at the next available call date. Long-Term Debt by Year of Maturity Assuming Callable Debt Redeemed at Next Available Call Date (Dollars in millions) 2018 $ 53,932 $ 100,446 2019 61,760 45,015 2020 39,712 25,202 2021 23,945 14,184 2022 8,463 7,353 Thereafter 55,563 51,175 Total debt of Fannie Mae (1) 243,375 243,375 Debt of consolidated trusts (2) 3,052,923 3,052,923 Total long-term debt $ 3,296,298 $ 3,296,298 __________ (1) Includes unamortized discounts and premiums, other cost basis adjustments and fair value adjustments of $752 million . (2) Contractual maturity of debt of consolidated trusts is not a reliable indicator of expected maturity because borrowers of the underlying loans generally have the right to prepay their obligations at any time.

Derivative Instruments

Derivative Instruments	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments	Derivative Instruments Derivative instruments are an integral part of our strategy in managing interest rate risk. Derivative instruments may be privately-negotiated, bilateral contracts, or they may be listed and traded on an exchange. We refer to our derivative transactions made pursuant to bilateral contracts as our over-the-counter (“OTC”) derivative transactions and our derivative transactions accepted for clearing by a derivatives clearing organization as our cleared derivative transactions. We typically do not settle the notional amount of our risk management derivatives; rather, notional amounts provide the basis for calculating actual payments or settlement amounts. The derivative contracts we use for interest rate risk management purposes fall into these broad categories: • Interest rate swap contracts. An interest rate swap is a transaction between two parties in which each party agrees to exchange payments tied to different interest rates or indices for a specified period of time, generally based on a notional amount of principal. The types of interest rate swaps we use include pay-fixed swaps, receive-fixed swaps and basis swaps. • Interest rate option contracts. These contracts primarily include pay-fixed swaptions, receive-fixed swaptions, cancelable swaps and interest rate caps. A swaption is an option contract that allows us or a counterparty to enter into a pay-fixed or receive-fixed swap at some point in the future. • Foreign currency swaps. These swaps convert debt that we issue in foreign denominated currencies into U.S. dollars. We enter into foreign currency swaps only to the extent that we hold foreign currency debt. • Futures. These are standardized exchange-traded contracts that either obligate a buyer to buy an asset at a predetermined date and price or a seller to sell an asset at a predetermined date and price. The types of futures contracts we enter into include Eurodollar, U.S. Treasury and swaps. We enter into various forms of credit risk-sharing agreements, including credit risk transfer transactions, swap credit enhancements and mortgage insurance contracts, that we account for as derivatives. The majority of our credit-related derivatives are credit risk transfer transactions, whereby a portion of the credit risk associated with losses on a reference pool of mortgage loans is transferred to a third party. We enter into forward purchase and sale commitments that lock in the future delivery of mortgage loans and mortgage-related securities at a fixed price or yield. Certain commitments to purchase mortgage loans and purchase or sell mortgage-related securities meet the criteria of a derivative. We typically settle the notional amount of our mortgage commitments that are accounted for as derivatives. We recognize all derivatives as either assets or liabilities in our consolidated balance sheets at their fair value. See “ Note 15, Fair Value ” for additional information on derivatives recorded at fair value. Notional and Fair Value Position of our Derivatives The following table displays the notional amount and estimated fair value of our asset and liability derivative instruments. As of December 31, 2017 As of December 31, 2016 Asset Derivatives Liability Derivatives Asset Derivatives Liability Derivatives Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value (Dollars in millions) Risk management derivatives: Swaps: Pay-fixed $ 52,732 $ 772 $ 70,211 $ (2,120 ) $ 29,540 $ 660 $ 94,584 $ (4,396 ) Receive-fixed 31,671 2,391 138,852 (1,764 ) 30,207 2,696 135,470 (1,552 ) Basis 873 124 — — 1,624 115 15,600 (11 ) Foreign currency 234 59 236 (56 ) 214 40 216 (85 ) Swaptions: Pay-fixed 9,750 95 4,000 (20 ) 9,600 241 4,850 (82 ) Receive-fixed 250 13 9,250 (304 ) — — 10,100 (257 ) Other (1) 13,240 22 7,315 (1 ) 15,087 33 655 (2 ) Total gross risk management derivatives 108,750 3,476 229,864 (4,265 ) 86,272 3,785 261,475 (6,385 ) Accrued interest receivable (payable) — 835 — (814 ) — 785 — (937 ) Netting adjustment (2) — (4,272 ) — 4,979 — (4,514 ) — 6,844 Total net risk management derivatives $ 108,750 $ 39 $ 229,864 $ (100 ) $ 86,272 $ 56 $ 261,475 $ (478 ) Mortgage commitment derivatives: Mortgage commitments to purchase whole loans $ 4,143 $ 9 $ 1,570 $ (2 ) $ 4,753 $ 28 $ 3,039 $ (49 ) Forward contracts to purchase mortgage-related securities 45,925 108 21,099 (21 ) 31,635 198 27,297 (388 ) Forward contracts to sell mortgage-related securities 19,320 15 85,556 (205 ) 34,103 405 47,645 (300 ) Total mortgage commitment derivatives 69,388 132 108,225 (228 ) 70,491 631 77,981 (737 ) Derivatives at fair value $ 178,138 $ 171 $ 338,089 $ (328 ) $ 156,763 $ 687 $ 339,456 $ (1,215 ) __________ (1) Includes futures and swap credit enhancements, as well as credit risk transfer transactions and mortgage insurance contracts that we account for as derivatives. (2) The netting adjustment represents the effect of the legal right to offset under legally enforceable master netting arrangements to settle with the same counterparty on a net basis, including cash collateral posted and received. Cash collateral posted was $1.4 billion and $2.9 billion as of December 31, 2017 and 2016 , respectively. Cash collateral received was $649 million and $535 million as of December 31, 2017 and 2016 , respectively. We record all derivative gains and losses, including accrued interest, in “Fair value losses, net” in our consolidated statements of operations and comprehensive income. The following table displays, by type of derivative instrument, the fair value gains and losses, net on our derivatives. For the Year Ended December 31, 2017 2016 2015 (Dollars in millions) Risk management derivatives: Swaps: Pay-fixed $ 1,296 $ 757 $ (746 ) Receive-fixed (851 ) (751 ) 625 Basis 21 (21 ) 4 Foreign currency 49 (76 ) (60 ) Swaptions: Pay-fixed (161 ) 163 135 Receive-fixed (60 ) (230 ) (93 ) Other 13 160 (25 ) Net accrual of periodic settlements (889 ) (1,125 ) (960 ) Total risk management derivatives fair value losses, net (582 ) (1,123 ) (1,120 ) Mortgage commitment derivatives fair value gains (losses), net (603 ) 288 (393 ) Total derivatives fair value losses, net $ (1,185 ) $ (835 ) $ (1,513 ) Derivative Counterparty Credit Exposure Our derivative counterparty credit exposure relates principally to interest rate derivative contracts. We are exposed to the risk that a counterparty in a derivative transaction will default on payments due to us, which may require us to seek a replacement derivative from a different counterparty. This replacement may be at a higher cost, or we may be unable to find a suitable replacement. We manage our derivative counterparty credit exposure relating to our risk management derivative transactions mainly through enforceable master netting arrangements, which allow us to net derivative assets and liabilities with the same counterparty or clearing organization and clearing member. For our OTC derivative transactions, we require counterparties to post collateral, which may include cash, U.S. Treasury securities, agency debt and agency mortgage-related securities. See “ Note 14, Netting Arrangements ” for information on our rights to offset assets and liabilities as of December 31, 2017 and 2016 .

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Tax	Income Taxes Provision for Federal Income Taxes We are subject to federal income tax, but we are exempt from state and local income taxes. The following table displays the components of our provision for federal income taxes. For the Year Ended December 31, 2017 2016 2015 (Dollars in millions) Current income tax benefit (provision) $ 600 $ (2,014 ) $ 271 Deferred income tax provision (1) (16,584 ) (4,006 ) (5,524 ) Provision for federal income taxes $ (15,984 ) $ (6,020 ) $ (5,253 ) __________ (1) Amount excludes the current income tax effect of items recognized directly in “Fannie Mae stockholders’ equity (deficit).” The current income tax benefit for the year ended December 31, 2017 reflects the recognition of a $3.7 billion income tax receivable from amended federal income tax returns to claim tax deductions for bad debts. This amount was offset by a corresponding $3.7 billion decrease in our net deferred tax assets, resulting in an increase in our deferred income tax provision. The deferred income tax provision for the year ended December 31, 2017 also reflects the impact of the legislation enacted in the fourth quarter of 2017, which reduced the federal corporate income tax rate to 21% effective January 1, 2018. The effect of this legislation reduced the value of our net deferred tax assets, resulting in an increase in our deferred income tax provision. The following table displays the difference between the statutory corporate tax rate and our effective tax rate. For the Year Ended December 31, 2017 2016 2015 Statutory corporate tax rate 35.0 % 35.0 % 35.0 % Equity investments in affordable housing projects (1.4 ) (1.9 ) (2.6 ) Effect of corporate tax rate change 53.6 — — Other (0.6 ) (0.3 ) 0.9 Valuation allowance — — (0.9 ) Effective tax rate 86.6 % 32.8 % 32.4 % Our effective tax rate is the provision for federal income taxes expressed as a percentage of income or loss before federal income taxes. Our effective tax rate was different from the federal statutory corporate rate of 35% for the year ended December 31, 2017 primarily due to the effect of the remeasurement of our net deferred tax assets in the fourth quarter of 2017 as a result of the legislation discussed above. Our effective tax rates for the years 2017 , 2016 and 2015 were impacted by the benefits of our investments in housing projects eligible for low-income housing tax credits. The decrease in our deferred tax valuation allowance in 2015 reflects the utilization of our capital loss carryforwards due to recognition of net capital gains, which allowed us to release the corresponding valuation allowance against our capital loss carryforwards. Deferred Tax Assets and Liabilities We recognize deferred tax assets and liabilities for future tax consequences arising from differences between the carrying amounts of existing assets and liabilities under GAAP and their respective tax bases. We evaluate our deferred tax assets for recoverability using a consistent approach which considers the relative impact of negative and positive evidence, including our historical profitability and projections of future taxable income. As of December 31, 2017 , we continued to conclude that the positive evidence in favor of the recoverability of our deferred tax asset outweighed the negative evidence and that it is more likely than not that our deferred tax assets will be realized. Our framework for assessing the recoverability of deferred tax assets requires us to weigh all available evidence, including: • the sustainability of recent profitability required to realize the deferred tax assets; • the cumulative net income or losses in our consolidated statements of operations and comprehensive income in recent years; • unsettled circumstances that, if unfavorably resolved, would adversely affect future operations and profit levels on a continuing basis in future years; • the funding available to us under the senior preferred stock purchase agreement; and • the carryforward periods for any tax credits. The following table displays our deferred tax assets and deferred tax liabilities. The deferred tax assets and liabilities as of December 31, 2016 were measured at the applicable statutory corporate tax rate of 35% for the period. The deferred tax assets and liabilities as of December 31, 2017 have been remeasured using the 21% statutory corporate tax rate enacted in the fourth quarter of 2017 with an effective date of January 1, 2018. As of December 31, 2017 2016 (Dollars in millions) Deferred tax assets: Mortgage and mortgage-related assets $ 10,397 $ 17,130 Allowance for loan losses and basis in acquired property, net 2,286 9,496 Debt and derivative instruments 1,205 2,989 Partnership credits 1,695 1,968 Partnership and other equity investments 311 667 Other, net 1,621 1,665 Total deferred tax assets 17,515 33,915 Deferred tax liabilities: Unrealized gains on AFS securities, net 165 385 Total deferred tax liabilities 165 385 Deferred tax assets, net $ 17,350 $ 33,530 As of December 31, 2017 , we had no net operating loss carryforwards and no capital loss carryforwards. We had a remaining balance of $1.7 billion of partnership tax credit carryforwards that expire in various years through 2037 and $837 million of alternative minimum tax credit carryforwards that will be used by the year 2021. Unrecognized Tax Benefits The following table displays the changes in our unrecognized tax benefits. For the Year Ended December 31, 2017 2016 2015 (Dollars in millions) Unrecognized tax benefits as of January 1 $ — $ — $ 213 Gross increases—tax positions in current year 514 — — Gross decreases—tax positions in prior years — — (213 ) Unrecognized tax benefits as of December 31 (1) $ 514 $ — $ — __________ (1) Amount excludes tax credits of $220 million as of December 31, 2017 . We had $514 million of unrecognized tax benefits as of December 31, 2017 . If these positions were to resolve favorably, our effective tax would be reduced in future periods by $205 million . We had no unrecognized tax benefits as of December 31, 2016 or December 31, 2015. Our tax years 2007 through 2016 remain open to assessment by the IRS.

Segment Reporting

Segment Reporting	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Segment Reporting	Segment Reporting We have two reportable business segments: Single-Family and Multifamily. Our CEO is the chief operating decision maker and allocates resources and assesses performance based on these two business segments. Results of our two business segments are intended to reflect each segment as if it were a stand-alone business. The sum of the results for our two business segments equals our consolidated results of operations. The section below provides a discussion of our business segments. Single-Family Business Segment • Works with our lender customers to acquire and securitize single-family mortgage loans delivered to us by lenders into Fannie Mae MBS. • Issues structured Fannie Mae MBS backed by single-family mortgage assets and provides other services to our lender customers. • Prices and manages the credit risk on loans in our single-family guaranty book of business. Also enters into transactions that transfer a portion of the credit risk on some of the loans in our single-family guaranty book of business. • Works to reduce costs of defaulted single-family loans through home retention solutions and foreclosure alternatives, management of foreclosures and our REO inventory, selling nonperforming loans and pursuing contractual remedies from lenders, servicers and providers of credit enhancement. Multifamily Business Segment • Works with our lender customers to acquire and securitize multifamily mortgage loans delivered to us by lenders into Fannie Mae MBS. • Issues structured multifamily Fannie Mae MBS through our Fannie Mae Guaranteed Multifamily Structures (“Fannie Mae GeMS TM ”) program and provides other services to our lender customers. • Prices and manages the credit risk on loans in our multifamily guaranty book of business. Lenders retain a portion of the credit risk in most multifamily transactions. • Works to maintain credit quality of the book, prevent foreclosure, reduce costs of defaulted multifamily loans, manage our REO inventory, and pursue contractual remedies from lenders, servicers and providers of credit enhancement. The following table displays total assets by segment. As of December 31, 2017 2016 2015 (Dollars in millions) Single-Family $ 3,057,904 $ 3,029,727 $ 2,993,495 Multifamily 287,625 258,241 228,422 Total assets $ 3,345,529 $ 3,287,968 $ 3,221,917 We operate our business solely in the United States and its territories, and accordingly, we generate no revenue from and have no long-lived assets, other than financial instruments, in geographic locations other than the United States and its territories. Segment Allocations and Results The majority of our revenues and expenses are directly associated with each respective business segment and are included in determining its operating results. Other revenues and expenses, including administrative expenses, that are not directly attributable to a particular business segment are allocated based on the size of each segment’s total book of business. The substantial majority of our gains and losses associated with our risk management derivatives are allocated to our Single-Family business segment. The following tables display our segment results. For the Year Ended December 31, 2017 Single-Family Multifamily Total (Dollars in millions) Net interest income (1) $ 18,212 $ 2,521 $ 20,733 Fee and other income (2) 1,378 849 2,227 Net revenues 19,590 3,370 22,960 Investment gains, net (3) 1,352 170 1,522 Fair value losses, net (4) (1,188 ) (23 ) (1,211 ) Administrative expenses (2,391 ) (346 ) (2,737 ) Credit-related income (expense): (5) Benefit (provision) for credit losses 2,090 (49 ) 2,041 Foreclosed property income (expense) (540 ) 19 (521 ) Total credit-related income (expense) 1,550 (30 ) 1,520 TCCA fees (6) (2,096 ) — (2,096 ) Other expenses, net (1,004 ) (507 ) (1,511 ) Income before federal income taxes 15,813 2,634 18,447 Provision for federal income taxes (14,301 ) (1,683 ) (15,984 ) Net income $ 1,512 $ 951 $ 2,463 For the Year Ended December 31, 2016 Single-Family Multifamily Total (Dollars in millions) Net interest income (1) $ 19,010 $ 2,285 $ 21,295 Fee and other income (2) 521 445 966 Net revenues 19,531 2,730 22,261 Investment gains, net (3) 944 312 1,256 Fair value losses, net (4) (1,040 ) (41 ) (1,081 ) Administrative expenses (2,418 ) (323 ) (2,741 ) Credit-related income: (5) Benefit for credit losses 2,092 63 2,155 Foreclosed property income (expense) (653 ) 9 (644 ) Total credit-related income 1,439 72 1,511 TCCA fees (6) (1,845 ) — (1,845 ) Other expenses, net (1,012 ) (16 ) (1,028 ) Income before federal income taxes 15,599 2,734 18,333 Provision for federal income taxes (5,417 ) (603 ) (6,020 ) Net income $ 10,182 $ 2,131 $ 12,313 For the Year Ended December 31, 2015 Single-Family Multifamily Total (Dollars in millions) Net interest income (1) $ 19,301 $ 2,108 $ 21,409 Fee and other income (2) 636 712 1,348 Net revenues 19,937 2,820 22,757 Investment gains, net (3) 970 366 1,336 Fair value losses, net (4) (1,505 ) (262 ) (1,767 ) Administrative expenses (2,711 ) (339 ) (3,050 ) Credit-related income (expense): (5) Benefit for credit losses 688 107 795 Foreclosed property income (expense) (1,723 ) 94 (1,629 ) Total credit-related income (expense) (1,035 ) 201 (834 ) TCCA fees (6) (1,621 ) — (1,621 ) Other income (expenses), net (831 ) 218 (613 ) Income before federal income taxes 13,204 3,004 16,208 Provision for federal income taxes (4,593 ) (660 ) (5,253 ) Net income 8,611 2,344 10,955 Less: Net income attributable to noncontrolling interest — (1 ) (1 ) Net income attributable to Fannie Mae $ 8,611 $ 2,343 $ 10,954 __________ (1) Net interest income primarily consists of guaranty fees received as compensation for assuming and managing the credit risk on loans underlying Fannie Mae MBS held by third parties for the respective business segment, and the difference between the interest income earned on the respective business segment’s mortgage assets in our retained mortgage portfolio and the interest expense associated with the debt funding those assets. Revenues from single-family guaranty fees include revenues generated by the 10 basis point increase in guaranty fees we implemented in 2012 pursuant to TCCA. (2) Single-Family fee and other income primarily consists of compensation for engaging in structured transactions and providing other lender services, and income resulting from settlement agreements resolving certain claims relating to private-label securities we purchased or that we have guaranteed. Multifamily fee and other income consists of fees associated with multifamily business activities, including yield maintenance income. (3) Investment gains and losses primarily consists of gains and losses on the sale of mortgage assets for the respective business segment. (4) Single-Family fair value gains and losses primarily consist of fair value gains and losses on risk management and mortgage commitment derivatives, trading securities and other financial instruments associated with our single-family total book of business. Multifamily fair value gains and losses primarily consist of fair value gains and losses on MBS commitment derivatives, trading securities and other financial instruments associated with our multifamily total book of business. (5) Credit-related income or expense is based on the guaranty book of business of the respective business segment and consists of the applicable segment’s benefit or provision for credit losses and foreclosed property expense on loans underlying the segment’s guaranty book of business. (6) Consists of the portion of our single-family guaranty fees that is remitted to Treasury pursuant to the TCCA.

Equity (Deficit)

Equity (Deficit)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Equity (Deficit)	Equity (Deficit) Common Stock Shares of common stock outstanding, net of shares held as treasury stock, totaled 1.2 billion as of December 31, 2017 and 2016 . During conservatorship, the rights and powers of shareholders are suspended. Accordingly, our common shareholders have no ability to elect directors or to vote on other matters during the conservatorship unless FHFA elects to delegate this authority to them. The senior preferred stock purchase agreement with Treasury prohibits the payment of dividends on common stock without the prior written consent of Treasury. The conservator also has eliminated common stock dividends. In addition, we issued a warrant to Treasury that provides Treasury with the right to purchase for a nominal price shares of our common stock equal to 79.9% of the total number of shares of common stock outstanding on a fully diluted basis on the date of exercise, which would substantially dilute the ownership in Fannie Mae of our common stockholders at the time of exercise. Refer to the “Senior Preferred Stock and Common Stock Warrant” section of this note for more information. Preferred Stock The following table displays our senior preferred stock and preferred stock outstanding. Issued and Outstanding as of December 31, Annual Dividend Rate as of December 31, 2017 2017 2016 Stated Value per Share Title Issue Date Shares Amount Shares Amount Redeemable on or After (Dollars and shares in millions, except per share amounts) Senior Preferred Stock Series 2008-2 September 8, 2008 1 $ 117,149 1 $ 117,149 $ 117,149 (1) N/A (2) N/A (3) Preferred Stock Series D September 30, 1998 3 $ 150 3 $ 150 $ 50 5.250 % September 30, 1999 Series E April 15, 1999 3 150 3 150 50 5.100 April 15, 2004 Series F March 20, 2000 14 690 14 690 50 0.730 (4) March 31, 2002 (5) Series G August 8, 2000 6 288 6 288 50 0.610 (6) September 30, 2002 (5) Series H April 6, 2001 8 400 8 400 50 5.810 April 6, 2006 Series I October 28, 2002 6 300 6 300 50 5.375 October 28, 2007 Series L April 29, 2003 7 345 7 345 50 5.125 April 29, 2008 Series M June 10, 2003 9 460 9 460 50 4.750 June 10, 2008 Series N September 25, 2003 5 225 5 225 50 5.500 September 25, 2008 Series O December 30, 2004 50 2,500 50 2,500 50 7.000 (7) December 31, 2007 Convertible Series 2004-I (8) December 30, 2004 — 2,492 — 2,492 100,000 5.375 January 5, 2008 Series P September 28, 2007 40 1,000 40 1,000 25 4.500 (9) September 30, 2012 Series Q October 4, 2007 15 375 15 375 25 6.750 September 30, 2010 Series R (10) November 21, 2007 21 530 21 530 25 7.625 November 21, 2012 Series S December 11, 2007 280 7,000 280 7,000 25 7.750 (11) December 31, 2010 (12) Series T (13) May 19, 2008 89 2,225 89 2,225 25 8.250 May 20, 2013 Total 556 $ 19,130 556 $ 19,130 __________ (1) Initial stated value per share was $1,000 . Based on our draws of funds under the senior preferred stock purchase agreement with Treasury, the stated value per share on December 31, 2017 was $117,149 . (2) Beginning in 2013, dividends on the senior preferred stock are calculated based on our net worth as of the end of the immediately preceding fiscal quarter less an applicable capital reserve amount. The applicable capital reserve amount was $600 million for each dividend period in 2017; however, the dividend payment for the fourth quarter of 2017 was reduced by $2.4 billion from the otherwise payable amount pursuant to the December 2017 letter agreement with Treasury. For each dividend period beginning in 2018, the applicable capital reserve amount will be $3.0 billion . (3) Any liquidation preference of our senior preferred stock in excess of $1.0 billion may be repaid through an issuance of common or preferred stock, which would require the consent of the conservator and Treasury. The initial $1.0 billion liquidation preference may be repaid only in conjunction with termination of Treasury’s funding commitment under the senior preferred stock purchase agreement. (4) Rate effective March 31, 2016. Variable dividend rate resets every two years at a per annum rate equal to the two-year Constant Maturity U.S. Treasury Rate (“CMT”) minus 0.16% with a cap of 11% per year. (5) Represents initial call date. Redeemable every two years thereafter. (6) Rate effective September 30, 2016. Variable dividend rate resets every two years at a per annum rate equal to the two-year CMT rate minus 0.18% with a cap of 11% per year. (7) Rate effective December 31, 2017 . Variable dividend rate resets quarterly thereafter at a per annum rate equal to the greater of 7.00% or 10-year CMT rate plus 2.375% . (8) Issued and outstanding shares were 24,922 as of December 31, 2017 and 2016 . (9) Rate effective December 31, 2017 . Variable dividend rate resets quarterly thereafter at a per annum rate equal to the greater of 4.50% or 3-Month LIBOR plus 0.75% . (10) On November 21, 2007, we issued 20 million shares of preferred stock in the amount of $500 million . Subsequent to the initial issuance, we issued an additional 1.2 million shares in the amount of $30 million on December 14, 2007 under the same terms as the initial issuance. (11) Rate effective December 31, 2017 . Variable dividend rate resets quarterly thereafter at a per annum rate equal to the greater of 7.75% or 3-Month LIBOR plus 4.23% . (12) Represents initial call date. Redeemable every five years thereafter. (13) On May 19, 2008, we issued 80 million shares of preferred stock in the amount of $2.0 billion . Subsequent to the initial issuance, we issued an additional 8 million shares in the amount of $200 million on May 22, 2008 and 1 million shares in the amount of $25 million on June 4, 2008 under the same terms as the initial issuance. As described under “Senior Preferred Stock and Common Stock Warrant,” we issued senior preferred stock that ranks senior to all other series of preferred stock as to both dividends and distributions upon dissolution, liquidation or winding up of the company. The senior preferred stock purchase agreement with Treasury also prohibits the payment of dividends on preferred stock (other than the senior preferred stock) without the prior written consent of Treasury. The conservator also has eliminated preferred stock dividends, other than dividends on the senior preferred stock. Each series of our preferred stock has no par value, is non-participating, is non-voting and has a liquidation preference equal to the stated value per share. None of our preferred stock is convertible into or exchangeable for any of our other stock or obligations, with the exception of the Convertible Series 2004-1. Shares of the Convertible Series 2004-1 Preferred Stock are convertible at any time, at the option of the holders, into shares of Fannie Mae common stock at a conversion price of $94.31 per share of common stock (equivalent to a conversion rate of 1,060.3329 shares of common stock for each share of Series 2004-1 Preferred Stock). The conversion price is adjustable, as necessary, to maintain the stated conversion rate into common stock. Events which may trigger an adjustment to the conversion price include certain changes in our common stock dividend rate, subdivisions of our outstanding common stock into a greater number of shares, combinations of our outstanding common stock into a smaller number of shares and issuances of any shares by reclassification of our common stock. No such events have occurred. Holders of preferred stock (other than the senior preferred stock) are entitled to receive non-cumulative, quarterly dividends when, and if, declared by our Board of Directors, but have no right to require redemption of any shares of preferred stock. Payment of dividends on preferred stock (other than the senior preferred stock) is not mandatory, but has priority over payment of dividends on common stock, which are also declared by the Board of Directors. If dividends on the preferred stock are not paid or set aside for payment for a given dividend period, dividends may not be paid on our common stock for that period. There were no dividends declared or paid on preferred stock (other than the senior preferred stock) for the years ended December 31, 2017 or 2016 . After a specified period, we have the option to redeem preferred stock (other than the senior preferred stock) at its redemption price plus the dividend (whether or not declared) for the then-current period accrued to, but excluding, the date of redemption. The redemption price is equal to the stated value for all issues of preferred stock except Series O, which has a redemption price of $50 to $52.50 depending on the year of redemption and Convertible Series 2004-1, which has a redemption price of $105,000 per share. Our preferred stock is traded in the over-the-counter market. Senior Preferred Stock and Common Stock Warrant On September 8, 2008, we issued to Treasury one million shares of Variable Liquidation Preference Senior Preferred Stock, Series 2008-2 (“senior preferred stock”), with an aggregate stated value and initial liquidation preference of $1.0 billion . On September 7, 2008, we issued a warrant to purchase common stock to Treasury. The warrant gives Treasury the right to purchase shares of our common stock equal to 79.9% of the total number of shares of common stock outstanding on a fully diluted basis on the date of exercise. The senior preferred stock and the warrant were issued to Treasury as an initial commitment fee in consideration of the commitment from Treasury to provide funds to us under the terms and conditions set forth in the senior preferred stock purchase agreement. We did not receive any cash proceeds as a result of issuing these shares or the warrant. We have assigned a value of $4.5 billion to Treasury’s commitment, which has been recorded as a reduction to additional paid-in-capital and was partially offset by the aggregate fair value of the warrant. There was no impact to the total balance of stockholders’ equity as a result of the issuance. Variable Liquidation Preference Senior Preferred Stock, Series 2008-2 Shares of the senior preferred stock have no par value and have a stated value and initial liquidation preference equal to $1,000 per share, for an aggregate initial liquidation preference of $1.0 billion . The liquidation preference of the senior preferred stock is subject to adjustment: • Any amounts Treasury pays to us pursuant to its funding commitment under the senior preferred stock purchase agreement are added to the liquidation preference. Treasury had paid us a total of $116.1 billion pursuant to this commitment as of December 31, 2017 , and will pay us an additional $3.7 billion to eliminate our net worth deficit as of December 31, 2017 . • Any quarterly commitment fees that are payable but not paid in cash to Treasury will be added to the liquidation preference. • For any dividend period for which dividends are payable, to the extent that dividends are not paid, they will accumulate and be added to the liquidation preference, regardless of whether or not they are declared. • The December 2017 letter agreement increased the aggregate liquidation preference of the senior preferred stock by $3.0 billion as of December 31, 2017. As a result of the adjustments described above, the aggregate liquidation preference of the senior preferred stock was $120.1 billion as of December 31, 2017 , and will increase to $123.8 billion after we receive the $3.7 billion in additional funds from Treasury to eliminate our net worth deficit as of December 31, 2017. Treasury, as the holder of the senior preferred stock, is entitled to receive, when, as and if declared, out of legally available funds, cumulative quarterly cash dividends. The dividends we have paid to Treasury on the senior preferred stock during conservatorship have been declared by, and paid at the direction of, our conservator, acting as successor to the rights, titles, powers and privileges of the Board of Directors. Dividends declared and paid on the senior preferred stock were $12.0 billion , $9.6 billion and $10.3 billion for the years ended December 31, 2017 , 2016 and 2015 , respectively. The dividend provisions of the senior preferred stock have been amended twice since the senior preferred stock was originally issued: in August 2012 through an amendment to the senior preferred stock purchase agreement and in December 2017 through a letter agreement. • August 2012 Amendment to Dividend Provisions (2013-2017). The August 2012 amendment changed the dividend provisions of the senior preferred stock to a “net worth sweep” dividend. For each quarterly dividend period, the dividend amount would be the amount, if any, by which our net worth as of the end of the immediately preceding fiscal quarter exceeded an applicable capital reserve amount. Our net worth as defined by the agreement is the amount, if any, by which our total assets (excluding Treasury’s funding commitment and any unfunded amounts related to the commitment) exceed our total liabilities (excluding any obligation in respect of capital stock), in each case as reflected on our balance sheet prepared in accordance with GAAP. The applicable capital reserve amount was initially $3.0 billion for dividend periods in 2013 and decreased by $600 million each year; therefore, the applicable capital reserve amount was $1.2 billion for dividend periods in 2016 and $600 million for dividend periods in 2017. Under the terms of the August 2012 amendment, the applicable capital reserve amount would have decreased to zero for dividend periods beginning January 1, 2018. These provisions were applicable from the first quarter of 2013 through the fourth quarter of 2017; however, the fourth quarter 2017 dividend payment was modified by the December 2017 letter agreement as described below. • December 2017 Amendment to Dividend Provisions (2018 and thereafter). The December 2017 letter agreement further modified the dividend provisions of the senior preferred stock. The dividends payable on the senior preferred stock continue to be net worth sweep dividends calculated each quarter based on our net worth as of the immediately preceding fiscal quarter less an applicable capital reserve amount. However, the applicable capital reserve amount for dividend periods beginning January 1, 2018 was increased to $3.0 billion . If we do not declare and pay the dividend amount in full for any dividend period for which dividends are payable, then the applicable capital reserve amount will thereafter be zero. The December 2017 letter agreement also reduced by $2.4 billion the dividend amount otherwise payable for the fourth quarter 2017 (which was calculated based on our net worth as of September 30, 2017, less the applicable capital reserve amount of $600 million as described above). As a result of these amended dividend payment provisions, for each quarterly period beginning with the first quarter of 2018, dividends on the senior preferred stock accumulate and are payable based on the amount by which our net worth as of the end of the immediately preceding fiscal quarter exceeds $3.0 billion . If our net worth does not exceed the applicable capital reserve amount of $3.0 billion as of the end of the immediately preceding fiscal quarter, then dividends will neither accumulate nor be payable for such period. We recognize a liability on our balance sheet for senior preferred stock dividends only upon their declaration by our conservator, at which point they become payable to the shareholder. On December 29, 2017 , we paid Treasury a fourth quarter 2017 dividend of $648 million on the senior preferred stock, reflecting our net worth of $3.6 billion as of September 30, 2017 , less the applicable capital reserve amount of $600 million and further reduced by an additional $2.4 billion as provided in the December 2017 letter agreement. Because we had a net worth deficit of $ 3.7 billion as of December 31, 2017 , no dividend will be payable to Treasury on the senior preferred stock for the first quarter of 2018. The senior preferred stock ranks prior to our common stock and all other outstanding series of our preferred stock, as well as any capital stock we issue in the future, as to both dividends and rights upon liquidation. As a result, if we are liquidated, the holder of the senior preferred stock is entitled to its then-current liquidation preference (which includes any accumulated but unpaid dividends) before any distribution is made to the holders of our common stock or other preferred stock. The senior preferred stock provides that we may not declare or pay dividends on, make distributions with respect to, or redeem, purchase or acquire, or make a liquidation payment with respect to, any common stock or other securities ranking junior to the senior preferred stock unless (1) full cumulative dividends on the outstanding senior preferred stock (including any unpaid dividends added to the liquidation preference) have been declared and paid in cash, and (2) all amounts required to be paid with the net proceeds of any issuance of capital stock for cash (as described in the following paragraph) have been paid in cash. In addition, as described below under “Senior Preferred Stock Purchase Agreement with Treasury—Covenants,” the covenants under the senior preferred stock purchase agreement require that we obtain Treasury’s prior written consent before declaring or paying any dividends or other distributions with respect to our equity securities (other than the senior preferred stock or the warrant) and before redeeming, purchasing, retiring or otherwise acquiring any of our equity securities (other than the senior preferred stock or the warrant). Shares of the senior preferred stock are not convertible. Shares of the senior preferred stock have no general or special voting rights, other than those set forth in the certificate of designation for the senior preferred stock or otherwise required by law. The consent of holders of at least two-thirds of all outstanding shares of senior preferred stock is generally required to amend the terms of the senior preferred stock or to create any class or series of stock that ranks prior to or on parity with the senior preferred stock. We are not permitted to redeem the senior preferred stock prior to the termination of Treasury’s funding commitment under the senior preferred stock purchase agreement. Moreover, we are not permitted to pay down the liquidation preference of the outstanding shares of senior preferred stock except to the extent of (1) accumulated and unpaid dividends previously added to the liquidation preference and not previously paid down; and (2) quarterly commitment fees previously added to the liquidation preference and not previously paid down. In addition to these exceptions, if we issue any shares of capital stock for cash while the senior preferred stock is outstanding (which requires Treasury’s approval), we are required to use the net proceeds of the issuance to pay down the liquidation preference of the senior preferred stock; however, the liquidation preference of each share of senior preferred stock may not be paid down below $1,000 per share prior to the termination of Treasury’s funding commitment. Following the termination of Treasury’s funding commitment, we may pay down the liquidation preference of all outstanding shares of senior preferred stock at any time, in whole or in part. Common Stock Warrant The warrant gives Treasury the right to purchase shares of our common stock equal to 79.9% of the total number of shares of our common stock outstanding on a fully diluted basis on the date of exercise. The warrant may be exercised in whole or in part at any time on or before September 7, 2028, by delivery to Fannie Mae of: (a) a notice of exercise; (b) payment of the exercise price of $0.00001 per share; and (c) the warrant. If the market price of one share of common stock is greater than the exercise price, in lieu of exercising the warrant by payment of the exercise price, Treasury may elect to receive shares equal to the value of the warrant (or portion thereof being canceled) pursuant to the formula specified in the warrant. Upon exercise of the warrant, Treasury may assign the right to receive the shares of common stock issuable upon exercise to any other person. If the warrant is exercised, the stated value of the common stock issued will be reclassified as “Common stock” in our consolidated balance sheets. As of February 14, 2018 , Treasury has not exercised the warrant. Senior Preferred Stock Purchase Agreement with Treasury Funding Commitment Under the senior preferred stock purchase agreement, Treasury made a commitment to provide funding, under certain conditions, to eliminate deficits in our net worth. We have received a total of $116.1 billion from Treasury pursuant to the senior preferred stock purchase agreement as of December 31, 2017 . Because we had a net worth deficit of $ 3.7 billion as of December 31, 2017 , we expect the Director of FHFA will submit a request to Treasury on our behalf for $3.7 billion to eliminate our net worth deficit. After we receive these additional funds, we will have received a total of $119.8 billion from Treasury pursuant to the senior preferred stock. If we have another net worth deficit in a future quarter, we will be required to obtain additional funding from Treasury pursuant to the senior preferred stock purchase agreement to avoid being placed into receivership. After we receive the additional funds requested from Treasury to eliminate our net worth deficit as of December 31, 2017, the maximum amount of remaining funding under the agreement will be $113.9 billion . If we were to draw additional funds from Treasury under the agreement in respect of a future period, the amount of remaining funding under the agreement would be reduced by the amount of our draw. Dividend payments we make to Treasury do not restore or increase the amount of funding available to us under the agreement. The amount of remaining funding under the agreement also would not change if the full quarterly dividend amount were not declared and paid to Treasury. The senior preferred stock purchase agreement provides that the deficiency amount will be calculated differently if we become subject to receivership or other liquidation process. The deficiency amount may be increased above the otherwise applicable amount upon our mutual written agreement with Treasury. In addition, if the Director of FHFA determines that the Director will be mandated by law to appoint a receiver for us unless our capital is increased by receiving funds under the commitment in an amount up to the deficiency amount (subject to the maximum amount that may be funded under the agreement), then FHFA, in its capacity as our conservator, may request that Treasury provide funds to us in such amount. The senior preferred stock purchase agreement also provides that, if we have a deficiency amount as of the date of completion of the liquidation of our assets, we may request funds from Treasury in an amount up to the deficiency amount (subject to the maximum amount that may be funded under the agreement). Any amounts that we draw under the senior preferred stock purchase agreement will be added to the liquidation preference of the senior preferred stock. No additional shares of senior preferred stock are required to be issued under the senior preferred stock purchase agreement. Commitment Fee The senior preferred stock purchase agreement provides for the payment of an unspecified quarterly commitment fee to Treasury; however, the August 2012 amendment to the agreement provided that this commitment fee will not be set, accrue or be payable, as long as the dividend provisions of the senior preferred stock remain substantially the same in form and content. Covenants The senior preferred stock purchase agreement provides that, until the senior preferred stock is repaid or redeemed in full, we may not, without the prior written consent of Treasury: • Declare or pay any dividend (preferred or otherwise) or make any other distribution with respect to any Fannie Mae equity securities (other than with respect to the senior preferred stock or warrant); • Redeem, purchase, retire or otherwise acquire any Fannie Mae equity securities (other than the senior preferred stock or warrant); • Sell or issue any Fannie Mae equity securities (other than the common stock issuable upon exercise of the warrant or as required by the terms of any binding agreement in effect on the date of the senior preferred stock purchase agreement); • Terminate the conservatorship (other than in connection with a receivership); • Sell, transfer, lease or otherwise dispose of any assets, other than dispositions for fair market value: (a) to a limited life regulated entity (in the context of receivership); (b) of assets and properties in the ordinary course of business, consistent with past practice; (c) of assets and properties having fair market value individually or in aggregate less than $250 million in one transaction or a series of related transactions; (d) in connection with a liquidation of Fannie Mae by a receiver; (e) of cash or cash equivalents for cash or cash equivalents; or (f) to the extent necessary to comply with the covenant described below relating to the reduction of our mortgage assets; • Incur indebtedness that would result in our aggregate indebtedness exceeding $407.2 billion through December 31, 2017 . For every year thereafter, our debt cap will equal 120% of the amount of mortgage assets we are allowed to own under the senior preferred stock purchase agreement on December 31 of the immediately preceding calendar year; • Issue any subordinated debt; • Enter into a corporate reorganization, recapitalization, merger, acquisition or similar event; or • Engage in transactions with affiliates unless the transaction is (a) pursuant to the senior preferred stock purchase agreement, the senior preferred stock or the warrant, (b) upon arm’s-length terms or (c) a transaction undertaken in the ordinary course or pursuant to a contractual obligation or customary employment arrangement in existence on the date of the senior preferred stock purchase agreement. The agreement, as amended, also provides that we may not own mortgage assets in excess of $288.4 billion as of December 31, 2017 or in excess of $250 billion as of December 31, 2018 and thereafter. In 2014, FHFA requested that we revise our portfolio plan to cap the portfolio each year at 90% of the annual limit under our senior preferred stock purchase agreement with Treasury. FHFA’s request noted that we may seek FHFA permission to increase this cap up to 95% of the annual limit under our senior preferred stock purchase agreement with Treasury upon written request and with a documented basis for exception, such as changed market conditions. Under the agreement, the effect of changes in generally accepted accounting principles that occurred subsequent to the date of the agreement and that require us to recognize additional mortgage assets in our consolidated balance sheets are not considered for purposes of evaluating our compliance with the limitation on the amount of mortgage assets we may own. In addition, the definition of indebtedness in the agreement was revised to clarify that it also does not give effect to any change that may be made in respect of the FASB guidance on accounting for transfers of financial assets or any similar accounting guidance. In addition, the agreement provides that we may not enter into any new compensation arrangements with, or increase amounts or benefits payable under existing compensation arrangements of, any named executive officer or other executive officer (each as defined by SEC rules) without the consent of the Director of FHFA, in consultation with the Secretary of the Treasury. As of December 31, 2017 , we were in compliance with the senior preferred stock purchase agreement covenants. We are required to provide an annual risk management plan to Treasury each year we remain in conservatorship. Each plan is required to set out our strategy for reducing our risk profile, describe the actions we will take to reduce the financial and operational risk associated with each of our business segments, and include an assessment of our performance against the planned actions described in the prior year’s plan. We submitted our most recent annual risk management plan to Treasury in December 2017 . Termination Provisions The senior preferred stock purchase agreement provides that Treasury’s funding commitment will terminate under any the following circumstances: (1) the completion of our liquidation and fulfillment of Treasury’s obligations under its funding commitment at that time, (2) the payment in full of, or reasonable provision for, all of our liabilities (whether or not contingent, including mortgage guaranty obligations), or (3) the funding by Treasury of the maximum amount under the agreement. In addition, Treasury may terminate its funding commitment and declare the senior preferred stock purchase agreement null and void if a court vacates, modifies, amends, conditions, enjoins, stays or otherwise affects the appointment of the conservator or otherwise curtails the conservator’s powers. Treasury may not terminate its funding commitment solely by reason of our being in conservatorship, receivership or other insolvency proceeding, or due to our financial condition or any adverse change in our financial condition. Waivers and Amendments The senior preferred stock purchase agreement provides that most provisions of the agreement may be waived or amended by mutual written agreement of the parties. No waiver or amendment of the agreement, however, may decrease Treasury’s aggregate funding commitment or add conditions to Treasury’s funding commitment if the waiver or amendment would adversely affect in any material respect the holders of our debt securities or guaranteed Fannie Mae MBS. Third-party Enforcement Rights If we default on payments with respect to our debt securities or guaranteed Fannie Mae MBS and Treasury fails to perform its obligations under its funding commitment, and if we and/or the conservator are not diligently pursuing remedies in respect of that failure, the holders of these debt securities or Fannie Mae MBS may file a claim for relief in the United States Court of Federal Claims. The relief, if granted, would require Treasury to fund to us the lesser of (1) the amount necessary to cure the payment defaults on our debt and Fannie Mae MBS and (2) the lesser of (a) the deficiency amount and (b) the maximum amount available under the agreement less the aggregate amount of funding previously provided under the commitment. Any payment that Treasury makes under those circumstances would be treated for all purposes as a draw under the senior preferred stock purchase agreement that would increase the liquidation preference of the senior preferred stock. Accumulated Other Comprehensive Income The following table displays our accumulated other comprehensive income, net of tax, by major categories. As of December 31, 2017 2016 2015 (Dollars in millions) Net unrealized gains on AFS securities for which we have not recorded OTTI $ 87 $ 135 $ 455 Net unrealized gains on AFS securities for which we have recorded OTTI 423 581 903 Other 43 43 49 Accumulated other comprehensive income $ 553 $ 759 $ 1,407 The following table displays changes in accumulated other comprehensive income, net of tax. For the Year Ended December 31, 2017 2016 AFS (1) Other Total AFS (1) Other Total (Dollars in millions) Beginning balance $ 716 $ 43 $ 759 $ 1,358 $ 49 $ 1,407 Other comprehensive income (loss) before reclassifications 53 8 61 (55 ) 2 (53 ) Amounts reclassified from other comprehensive income (259 ) (8 ) (267 ) (587 ) (8 ) (595 ) Net other comprehensive loss (206 ) — (206 ) (642 ) (6 ) (648 ) Ending balance $ 510 $ 43 $ 553 $ 716 $ 43 $ 759 __________ (1) The amounts reclassified from accumulated other comprehensive income represent the gain or loss recognized in earnings due to a sale of an AFS security or the recognition of a net impairment recognized in earnings, which are recorded in “ Investment gains, net ” in our consolidated statements of operations and comprehensive income.

Regulatory Capital Requirements

Regulatory Capital Requirements	12 Months Ended
	Dec. 31, 2017
Regulatory Capital Requirements [Abstract]
Regulatory Capital Requirements	Regulatory Capital Requirements FHFA stated that, during conservatorship, our existing statutory and FHFA-directed regulatory capital requirements will not be binding and FHFA will not issue quarterly capital classifications. We submit capital reports to FHFA and FHFA monitors our capital levels. FHFA has stated that it does not intend to report our critical capital, risk-based capital or subordinated debt levels during the conservatorship. Our regulatory capital classification measures are determined based on guidance from FHFA, in which FHFA (1) directed us, for loans backing Fannie Mae MBS held by third parties, to continue reporting our minimum capital requirements based on 0.45% of the unpaid principal balance and critical capital based on 0.25% of the unpaid principal balance, regardless of whether these loans have been consolidated pursuant to accounting rules, and (2) issued a regulatory interpretation stating that our minimum capital requirements are not automatically affected by the consolidation accounting guidance. Additionally, our regulatory capital classification measures exclude the funds provided to us by Treasury pursuant to the senior preferred stock purchase agreement, as the senior preferred stock does not qualify as core capital due to its cumulative dividend provisions. FHFA has directed us, during the time we are under conservatorship, to focus on managing to a positive net worth. We had a net worth deficit of $3.7 billion as of December 31, 2017 . We had a positive net worth of $6.1 billion as of December 31, 2016 . The following table displays our regulatory capital classification measures. As of December 31, 2017 2016 (Dollars in millions) Core capital (1) $ (121,389 ) $ (111,836 ) Statutory minimum capital requirement (2) 23,007 24,351 Deficit of core capital over statutory minimum capital requirement $ (144,396 ) $ (136,187 ) __________ (1) The sum of (a) the stated value of our outstanding common stock (common stock less treasury stock); (b) the stated value of our outstanding non-cumulative perpetual preferred stock; (c) our paid-in capital; and (d) our retained earnings (accumulated deficit). Core capital does not include: (a) accumulated other comprehensive income or (b) senior preferred stock. (2) Generally, the sum of (a) 2.50% of on-balance sheet assets, except those underlying Fannie Mae MBS held by third parties; (b) 0.45% of the unpaid principal balance of outstanding Fannie Mae MBS held by third parties; and (c) up to 0.45% of other off-balance sheet obligations, which may be adjusted by the Director of FHFA under certain circumstances. Our critical capital requirement is generally equal to the sum of: (1) 1.25% of on-balance sheet assets, except those underlying Fannie Mae MBS held by third parties; (2) 0.25% of the unpaid principal balance of outstanding Fannie Mae MBS held by third parties; and (3) 0.25% of other off-balance sheet obligations, which may be adjusted by the Director of FHFA under certain circumstances. As of December 31, 2017 and 2016 , we had a minimum capital deficiency of $144.4 billion and $136.2 billion , respectively. See “ Note 1, Summary of Significant Accounting Policies ” and “ Note 11, Equity (Deficit) ” for more information on capital and the terms of our senior preferred stock purchase agreement with Treasury and the senior preferred stock we issued to Treasury. Set forth below are additional restrictions related to our capital requirements. Restrictions on Capital Distributions and Dividends Statutory Restrictions. Under the GSE Act, FHFA has authority to prohibit capital distributions, including payment of dividends, if we fail to meet our capital requirements. If FHFA classifies us as significantly undercapitalized, we must obtain the approval of the Director of FHFA for any dividend payment. Under the Charter Act and the GSE Act, we are not permitted to make a capital distribution if, after making the distribution, we would be undercapitalized. The Director of FHFA, however, may permit us to repurchase shares if the repurchase is made in connection with the issuance of additional shares or obligations in at least an equivalent amount and will reduce our financial obligations or otherwise improve our financial condition. Restrictions Relating to Conservatorship. Our conservator announced on September 7, 2008 that we would not pay any dividends on the common stock or on any series of preferred stock, other than the senior preferred stock. In addition, FHFA’s regulations relating to conservatorship and receivership operations prohibit us from paying any dividends while in conservatorship unless authorized by the Director of FHFA. The Director of FHFA has directed us to make dividend payments on the senior preferred stock on a quarterly basis for every dividend period for which dividends were payable. Restrictions Under Senior Preferred Stock Purchase Agreement. The senior preferred stock purchase agreement prohibits us from declaring or paying any dividends on Fannie Mae equity securities (other than the senior preferred stock) without the prior written consent of Treasury. In addition, pursuant to the dividend provisions of the senior preferred stock and quarterly directives from our conservator, we are obligated to pay Treasury each quarter any dividends declared consisting of the amount, if any, by which our net worth as of the end of the immediately preceding fiscal quarter exceeds an applicable capital reserve amount, which is $3.0 billion effective January 1, 2018. As a result, our net income is not available to common stockholders. For more information on the terms of the senior preferred stock purchase agreement and senior preferred stock, see “ Note 11, Equity (Deficit) .” Additional Restrictions Relating to Preferred Stock. Payment of dividends on our common stock is also subject to the prior payment of dividends on our preferred stock and our senior preferred stock. Payment of dividends on all outstanding preferred stock, other than the senior preferred stock, is also subject to the prior payment of dividends on the senior preferred stock.

Concentrations of Credit Risk

Concentrations of Credit Risk	12 Months Ended
	Dec. 31, 2017
Risks and Uncertainties [Abstract]
Concentrations of Credit Risk	Concentrations of Credit Risk Concentrations of credit risk arise when a number of customers and counterparties engage in similar activities or have similar economic characteristics that make them susceptible to similar changes in industry conditions, which could affect their ability to meet their contractual obligations. Based on our assessment of business conditions that could impact our financial results, we have determined that concentrations of credit risk exist among: • single-family and multifamily borrowers (including geographic concentrations and loans with certain higher-risk characteristics); • mortgage insurers; • mortgage sellers and servicers; • financial guarantors; • multifamily lenders with risk sharing; and • derivative counterparties and parties associated with our off-balance sheet transactions. Concentrations for each of these groups are discussed below. Single-Family Loan Borrowers Regional economic conditions may affect a borrower’s ability to repay his or her mortgage loan and the property value underlying the loan. Geographic concentrations increase the exposure of our portfolio to changes in credit risk. Single-family borrowers are primarily affected by home prices and interest rates. To manage credit risk and comply with legal requirements, we typically require primary mortgage insurance or other credit enhancements if the current LTV ratio ( i.e. , the ratio of the unpaid principal balance of a loan to the current value of the property that serves as collateral) of a single-family conventional mortgage loan is greater than 80% when the loan is delivered to us. Multifamily Loan Borrowers Numerous factors affect a multifamily borrower’s ability to repay the loan and the value of the property underlying the loan. Multifamily loans are generally non-recourse to the borrower. The most significant factors affecting credit risk are rental income, capitalization rates for the mortgaged property, and general economic conditions. The average unpaid principal balance for multifamily loans is significantly larger than for single-family borrowers and, therefore, individual defaults for multifamily borrowers can result in more significant losses. We continually monitor the performance and risk characteristics of our multifamily loans, underlying properties and borrowers on an ongoing basis. As part of our multifamily risk management activities, we perform detailed loan reviews that evaluate borrower and geographic concentrations, lender qualifications, counterparty risk, property performance and contract compliance. We generally require mortgage servicers to submit periodic property operating information and condition reviews, allowing us to monitor the performance of individual loans. We use this information to evaluate the credit quality of our portfolio, identify potential problem loans and initiate appropriate loss mitigation activities. The following table displays the regional geographic concentration of single-family and multifamily loans in our guaranty book of business, measured by the unpaid principal balance of the loans. Geographic Concentration (1) Percentage of Single-Family Conventional Guaranty Book of Business (2) Percentage of Multifamily Guaranty Book of Business (3) As of December 31, As of December 31, 2017 2016 2017 2016 Midwest 15 % 15 % 9 % 9 % Northeast 18 18 15 16 Southeast 22 22 26 25 Southwest 17 17 23 22 West 28 28 27 28 Total 100 % 100 % 100 % 100 % __________ (1) Midwest consists of IL, IN, IA, MI, MN, NE, ND, OH, SD, WI; Northeast consists of CT, DE, ME, MA, NH, NJ, NY, PA, PR, RI, VT, VI; Southeast consists of AL, DC, FL, GA, KY, MD, MS, NC, SC, TN, VA, WV; Southwest consists of AZ, AR, CO, KS, LA, MO, NM, OK, TX, UT; West consists of AK, CA, GU, HI, ID, MT, NV, OR, WA and WY. (2) Consists of the portion of our single-family conventional guaranty book of business for which we have detailed loan level information, which constituted over 99% of our total single-family conventional guaranty book of business as of December 31, 2017 and 2016 . (3) Consists of the portion of our multifamily guaranty book of business for which we have detailed loan level information, which constituted 99% of our total multifamily guaranty book of business as of December 31, 2017 and 2016 . Risk Characteristics of our Guaranty Book of Business One of the measures by which we gauge our performance risk under our guaranty is the delinquency status of the mortgage loans we hold in our retained mortgage portfolio, or in the case of mortgage-backed securities, the mortgage loans underlying the related securities. For single-family loans, management monitors the serious delinquency rate, which is the percentage of single-family loans 90 days or more past due or in the foreclosure process, and loans that have higher risk characteristics, such as high mark-to-market LTV ratios. For multifamily loans, management monitors the serious delinquency rate, which is the percentage of loans, based on unpaid principal balance, that are 60 days or more past due, and other loans that have higher risk characteristics, to determine our overall credit quality indicator. Higher risk characteristics include, but are not limited to, current DSCR below 1.0 and high original LTV ratios. We stratify multifamily loans into different internal risk categories based on the credit risk inherent in each individual loan. For single-family and multifamily loans, we use this information, in conjunction with housing market and economic conditions, to structure our pricing and our eligibility and underwriting criteria to reflect the current risk of loans with these higher-risk characteristics, and in some cases we decide to significantly reduce our participation in riskier loan product categories. Management also uses this data together with other credit risk measures to identify key trends that guide the development of our loss mitigation strategies. The following tables display the delinquency status and serious delinquency rates for specified loan categories of our single-family conventional and total multifamily guaranty book of business. As of December 31, 2017 (1) 2016 (1) 30 Days Delinquent 60 Days Delinquent Seriously Delinquent (2) 30 Days Delinquent 60 Days Delinquent Seriously Delinquent (2) Percentage of single-family conventional guaranty book of business (3) 1.42 % 0.43 % 1.15 % 1.30 % 0.36 % 1.18 % Percentage of single-family conventional loans (4) 1.63 0.50 1.24 1.51 0.41 1.20 As of December 31, 2017 (1) 2016 (1) Percentage of (3) Seriously Delinquent Rate (2) Percentage of (3) Seriously Delinquent Rate (2) Estimated mark-to-market loan-to-value ratio: Greater than 100% 1 % 11.70 % 2 % 10.44 % Geographical distribution: California 19 0.42 19 0.50 Florida 6 3.71 6 1.89 New Jersey 4 2.15 4 3.07 New York 5 2.02 5 2.65 All other states 66 1.09 66 1.11 Product distribution: Alt-A 2 4.95 3 5.00 Vintages: 2004 and prior 4 3.28 5 2.82 2005-2008 6 6.55 8 6.39 2009-2017 90 0.53 87 0.36 __________ (1) Consists of the portion of our single-family conventional guaranty book of business for which we have detailed loan level information, which constituted approximately 99% of our total single-family conventional guaranty book of business as of December 31, 2017 and 2016 . (2) Consists of single-family conventional loans that were 90 days or more past due or in the foreclosure process as of December 31, 2017 and 2016 . (3) Calculated based on the aggregate unpaid principal balance of single-family conventional loans for each category divided by the aggregate unpaid principal balance of loans in our single-family conventional guaranty book of business. (4) Calculated based on the number of single-family conventional loans that were delinquent divided by the total number of loans in our single-family conventional guaranty book of business. As of December 31, 2017 (1)(2) 2016 (1)(2) 30 Days Delinquent Seriously Delinquent (3) 30 Days Delinquent Seriously Delinquent (3) Percentage of multifamily guaranty book of business 0.03 % 0.11 % 0.02 % 0.05 % As of December 31, 2017 (1) 2016 (1) Percentage of Multifamily Guaranty Book of Business (2) Percentage Seriously Delinquent (3)(4) Percentage of Multifamily Guaranty Book of Business (2) Percentage Seriously Delinquent (3)(4) Original LTV ratio: Greater than 80% 2 % 0.21 % 2 % 0.22 % Less than or equal to 80% 98 0.11 98 0.05 Current DSCR less than 1.0 (5) 2 1.96 2 1.96 __________ (1) Consists of the portion of our multifamily guaranty book of business for which we have detailed loan level information, which constituted approximately 99% of our total multifamily guaranty book of business as of December 31, 2017 and 2016 , excluding loans that have been defeased. (2) Calculated based on the aggregate unpaid principal balance of multifamily loans for each category divided by the aggregate unpaid principal balance of loans in our multifamily guaranty book of business. (3) Consists of multifamily loans that were 60 days or more past due as of the dates indicated. (4) Calculated based on the unpaid principal balance of multifamily loans that were seriously delinquent divided by the aggregate unpaid principal balance of multifamily loans for each category included in our guaranty book of business. (5) Our estimates of current DSCRs are based on the latest available income information for these properties. Although we use the most recently available results of our multifamily borrowers, there is a lag in reporting, which typically can range from 3 to 6 months but in some cases may be longer. Other Concentrations Mortgage Insurers. Mortgage insurance “risk in force” refers to our maximum potential loss recovery under the applicable mortgage insurance policies. We had total mortgage insurance risk in force of $138.5 billion and $126.2 billion on the single-family mortgage loans in our guaranty book of business as of December 31, 2017 and 2016 , respectively, which represented 5% and 4% of our single-family guaranty book of business as of December 31, 2017 and December 31, 2016 , respectively. Our primary mortgage insurance risk in force was $137.9 billion and $125.6 billion as of December 31, 2017 and 2016 , respectively. Our pool mortgage insurance risk in force was $519 million and $617 million as of December 31, 2017 and 2016 , respectively. Our top three mortgage insurance companies provided 65% of our mortgage insurance risk in force as of December 31, 2017 and 66% as of December 31, 2016 . Mortgage insurance does not protect us from all losses on covered loans. For example, mortgage insurance does not cover us from default risk for properties that suffered damages that were not covered by the hazard insurance we require. Specifically, a property damaged by a flood that was outside a flood hazard area, where we require coverage, or a property damaged by an earthquake are the most likely scenarios where property damage may result in a default not covered by hazard insurance. Three of our mortgage insurer counterparties that are currently not approved to write new business are in run-off: PMI Mortgage Insurance Co. (“PMI”), Triad Guaranty Insurance Corporation (“Triad”) and Republic Mortgage Insurance Company (“RMIC”). Entering run-off may close off a source of profits and liquidity that may have otherwise assisted a mortgage insurer in paying claims under insurance policies, and could also cause the quality and speed of its claims processing to deteriorate. These three mortgage insurers provided a combined $6.1 billion , or 4% , of our risk in force mortgage insurance coverage of our single-family guaranty book of business as of December 31, 2017 . PMI and Triad have been paying only a portion of policyholder claims and deferring the remaining portion. PMI is currently paying 71.5% of claims under its mortgage insurance policies in cash and is deferring the remaining 28.5% , and Triad is currently paying 75% of claims in cash and deferring the remaining 25% . It is uncertain whether PMI or Triad will be permitted in the future to pay any remaining deferred policyholder claims and/or increase or decrease the amount of cash they pay on claims. RMIC is no longer deferring payments on policyholder claims and has paid us its previously outstanding deferred payment obligations as well as interest on those obligations; however, RMIC remains in run-off. We have counterparty credit risk relating to the potential insolvency of, or non-performance by, mortgage insurers that insure single-family loans we purchase or guarantee. There is risk that these counterparties may fail to fulfill their obligations to pay our claims under insurance policies. If we determine that it is probable that we will not collect all of our claims from one or more of our mortgage insurer counterparties, it could increase our loss reserves, which could adversely affect our results of operations, liquidity, financial condition and net worth. When we estimate the credit losses that are inherent in our mortgage loans and under the terms of our guaranty obligations we also consider the recoveries that we will receive on primary mortgage insurance, as mortgage insurance recoveries would reduce the severity of the loss associated with defaulted loans. We evaluate the financial condition of our mortgage insurer counterparties and adjust the contractually due recovery amounts to ensure that only probable losses as of the balance sheet date are included in our loss reserve estimate. As a result, if our assessment of one or more of our mortgage insurer counterparties’ ability to fulfill their respective obligations to us worsens, it could increase our combined loss reserves. As of December 31, 2017 and 2016 , the amount by which our estimated benefit from mortgage insurance reduced our combined loss reserves was $989 million and $1.4 billion , respectively. When an insured loan held in our retained mortgage portfolio subsequently goes into foreclosure, we charge off the loan, eliminating any previously-recorded loss reserves, and record REO and a mortgage insurance receivable for the claim proceeds deemed probable of recovery, as appropriate. However, if a mortgage insurer rescinds, cancels or denies insurance coverage, the initial receivable becomes due from the mortgage seller or servicer. We had outstanding receivables of $858 million recorded in “Other assets” in our consolidated balance sheets as of December 31, 2017 and $1.0 billion as of December 31, 2016 related to amounts claimed on insured, defaulted loans excluding government insured loans. Of this amount, $75 million as of December 31, 2017 and $141 million as of December 31, 2016 was due from our mortgage sellers or servicers. We assessed the total outstanding receivables for collectibility, and they are recorded net of a valuation allowance of $593 million as of December 31, 2017 and $638 million as of December 31, 2016 . The valuation allowance reduces our claim receivable to the amount which is considered probable of collection as of December 31, 2017 and 2016 . Mortgage Servicers and Sellers. Mortgage servicers collect mortgage and escrow payments from borrowers, pay taxes and insurance costs from escrow accounts, monitor and report delinquencies, and perform other required activities on our behalf. Our mortgage sellers and servicers may also be obligated to repurchase loans or foreclosed properties, reimburse us for losses or provide other remedies under certain circumstances, such as if it is determined that the mortgage loan did not meet our underwriting or eligibility requirements, if certain loan representations and warranties are violated or if mortgage insurers rescind coverage. However, under our revised representation and warranty framework, we no longer require repurchase for loans that have breaches of certain selling representations and warranties if they have met specified criteria for relief. Our business with mortgage servicers is concentrated. Our five largest depository single-family mortgage servicers, including their affiliates, serviced approximately 35% of our single-family guaranty book of business as of December 31, 2017 , compared with approximately 36% as of December 31, 2016 . Our five largest non-depository single-family mortgage servicers, including their affiliates, serviced approximately 20% of our single-family guaranty book of business as of December 31, 2017 , compared with approximately 16% as of December 31, 2016 . Our five largest multifamily mortgage servicers, including their affiliates, serviced approximately 48% of our multifamily guaranty book of business as of December 31, 2017 , compared with approximately 47% as of December 31, 2016 . If a significant mortgage seller or servicer counterparty, or a number of mortgage sellers or servicers, fails to meet their obligations to us, it could increase our credit losses and credit-related expense, and adversely affect our results of operations and financial condition. Financial Guarantors. We are the beneficiary of non-governmental financial guarantees on non-agency securities held in our retained mortgage portfolio and on non-agency securities that have been resecuritized to include a Fannie Mae guaranty and sold to third parties. The total unpaid principal balance of guaranteed non-agency securities in our retained mortgage portfolio was $849 million and $1.4 billion as of December 31, 2017 and 2016 , respectively. If a financial guarantor fails to meet its obligations to us with respect to the securities for which we have obtained financial guarantees, it could reduce the fair value of our mortgage-related securities and result in financial losses to us, which could have an adverse effect on our earnings, liquidity, financial condition and net worth. With the exception of Ambac Assurance Corporation (“Ambac”), which is operating under a deferred payment obligation and paying 45% on policyholder claims, none of our remaining non-governmental financial guarantor counterparties has failed to repay us for claims under guaranty contracts. Ambac provided coverage on $308 million , or 36% , of our total non-governmental financial guarantees on non-agency securities held in our retained mortgage portfolio as of December 31, 2017 . When assessing our securities for impairment, we consider the benefit of non-governmental financial guarantees from those guarantors that we determine are creditworthy, although we continue to seek collection of any amounts due to us from all counterparties. We are also the beneficiary of financial guarantees included in securities issued by Freddie Mac, the federal government and its agencies that totaled $9.5 billion as of December 31, 2017 and $11.6 billion as of December 31, 2016 . Multifamily Lenders with Risk Sharing. We enter into risk sharing agreements with lenders pursuant to which the lenders agree to bear all or some portion of the credit losses on the covered loans. Our maximum potential loss recovery from lenders under these risk sharing agreements on both Delegated Underwriting and Servicing (“DUS”) and non-DUS multifamily loans was $63.4 billion as of December 31, 2017 , compared with $54.8 billion as of December 31, 2016 . As of December 31, 2017 and December 31, 2016 , 43% of our maximum potential loss recovery on multifamily loans was from four DUS lenders. Derivatives Counterparties. For information on credit risk associated with our derivative transactions and repurchase agreements see “ Note 8, Derivative Instruments ” and “ Note 14, Netting Arrangements .”

Netting Arrangements

Netting Arrangements	12 Months Ended
	Dec. 31, 2017
Offsetting [Abstract]
Netting Arrangements	Netting Arrangements We use master netting arrangements, which allow us to offset certain financial instruments and collateral with the same counterparty, to minimize counterparty credit exposure. The tables below display information related to derivatives, securities purchased under agreements to resell or similar arrangements, and securities sold under agreements to repurchase or similar arrangements, which are subject to an enforceable master netting arrangement or similar agreement that are either offset or not offset in our consolidated balance sheets. As of December 31, 2017 Gross Amount Offset (1) Net Amount Presented in our Consolidated Balance Sheets Amounts Not Offset in our Consolidated Balance Sheets Gross Amount Financial Instruments (2) Collateral (3) Net Amount (Dollars in millions) Assets: OTC risk management derivatives $ 2,479 $ (2,464 ) $ 15 $ — $ — $ 15 Cleared risk management derivatives 1,811 (1,808 ) 3 — — 3 Mortgage commitment derivatives 132 — 132 (117 ) (1 ) 14 Total derivative assets 4,422 (4,272 ) 150 (4 ) (117 ) (1 ) 32 Securities purchased under agreements to resell or similar arrangements (5) 44,670 — 44,670 — (44,670 ) — Total assets $ 49,092 $ (4,272 ) $ 44,820 $ (117 ) $ (44,671 ) $ 32 Liabilities: OTC risk management derivatives $ (3,045 ) $ 2,957 $ (88 ) $ — $ — $ (88 ) Cleared risk management derivatives (2,033 ) 2,022 (11 ) — 11 — Mortgage commitment derivatives (228 ) — (228 ) 117 93 (18 ) Total derivative liabilities (5,306 ) 4,979 (327 ) (4 ) 117 104 (106 ) Total liabilities $ (5,306 ) $ 4,979 $ (327 ) $ 117 $ 104 $ (106 ) As of December 31, 2016 Gross Amount Offset (1) Net Amount Presented in our Consolidated Balance Sheets Amounts Not Offset in our Consolidated Balance Sheets Gross Amount Financial Instruments (2) Collateral (3) Net Amount (Dollars in millions) Assets: OTC risk management derivatives $ 3,688 $ (3,667 ) $ 21 $ — $ — $ 21 Cleared risk management derivatives 849 (847 ) 2 — — 2 Mortgage commitment derivatives 631 — 631 (357 ) (22 ) 252 Total derivative assets 5,168 (4,514 ) 654 (4 ) (357 ) (22 ) 275 Securities purchased under agreements to resell or similar arrangements (5) 51,115 — 51,115 — (51,115 ) — Total assets $ 56,283 $ (4,514 ) $ 51,769 $ (357 ) $ (51,137 ) $ 275 Liabilities: OTC risk management derivatives $ (4,905 ) $ 4,520 $ (385 ) $ — $ — $ (385 ) Cleared risk management derivatives (2,415 ) 2,324 (91 ) — 91 — Mortgage commitment derivatives (737 ) — (737 ) 357 16 (364 ) Total derivative liabilities (8,057 ) 6,844 (1,213 ) (4 ) 357 107 (749 ) Total liabilities $ (8,057 ) $ 6,844 $ (1,213 ) $ 357 $ 107 $ (749 ) ________ (1) Represents the effect of the right to offset under legally enforceable master netting arrangements to settle with the same counterparty on a net basis, including cash collateral posted and received and accrued interest. (2) Mortgage commitment derivative amounts reflect where we have recognized both an asset and a liability with the same counterparty under an enforceable master netting arrangement but we have not elected to offset the related amounts in our consolidated balance sheets. (3) Represents collateral received that has not been recognized and not offset in our consolidated balance sheets as well as collateral posted which has been recognized but not offset in our consolidated balance sheets. Does not include collateral held or posted in excess of our exposure. The fair value of non-cash collateral we pledged was $747 million and $1.3 billion as of December 31, 2017 and December 31, 2016 , respectively, which the counterparty was permitted to sell or repledge. The fair value of non-cash collateral received was $44.7 billion and $51.2 billion , of which $42.5 billion and $45.5 billion could be sold or repledged as of December 31, 2017 and December 31, 2016 , respectively. None of the underlying collateral was sold or repledged as of December 31, 2017 and December 31, 2016 . (4) Excludes derivative assets of $21 million and $33 million as of December 31, 2017 and 2016 , respectively, and derivative liabilities of $1 million and $2 million recognized in our consolidated balance sheets as of December 31, 2017 and 2016 , respectively, that are not subject to enforceable master netting arrangements. (5) Includes $25.2 billion and $20.7 billion of securities purchased under agreements to resell classified as “Cash and cash equivalents” in our consolidated balance sheets as of December 31, 2017 and 2016 , respectively. Derivative instruments are recorded at fair value and securities purchased under agreements to resell or similar arrangements are recorded at amortized cost in our consolidated balance sheets. We determine our rights to offset the assets and liabilities presented above with the same counterparty, including collateral posted or received, based on the contractual arrangements entered into with our individual counterparties and various rules and regulations that would govern the insolvency of a derivative counterparty. The following is a description, under various agreements, of the nature of those rights and their effect or potential effect on our financial position. The terms of the majority of our contracts for OTC risk management derivatives are governed under master agreements of the International Swaps and Derivatives Association Inc. (“ISDA”). These agreements provide that all transactions entered into under the agreement with the counterparty constitute a single contractual relationship. An event of default by the counterparty allows the early termination of all outstanding transactions under the same ISDA agreement and we may offset all outstanding amounts related to the terminated transactions including collateral posted or received. The terms of our contracts for cleared derivatives are governed under the rules of the clearing organization and the agreement between us and the clearing member of that clearing organization. In the event of a clearing organization default, all open positions at the clearing organization are closed and a net position (on a clearing member by clearing member basis) is calculated. Unless otherwise transferred, in the event of a clearing member default, all open positions cleared through that clearing member are closed and a net position is calculated. The terms of our contracts for mortgage commitment derivatives are primarily governed by the Fannie Mae Single-Family Selling Guide (“Guide”), for Fannie Mae-approved lenders, or Master Securities Forward Transaction Agreements (“MSFTA”), for counterparties that are not Fannie Mae-approved lenders. In the event of default by the counterparty, both the Guide and the MSFTA allow us to terminate all outstanding transactions under the applicable agreement and offset all outstanding amounts related to the terminated transactions including collateral posted or received. Under the Guide, upon a lender event of default, we generally may offset any amounts owed to a lender against any amounts a lender may owe us under any other existing agreement, regardless of whether or not such other agreements are in default or payments are immediately due. The terms of our contracts for securities purchased under agreements to resell and securities sold under agreements to repurchase are governed by Master Repurchase Agreements, which are based on the guidelines prescribed by the Securities Industry and Financial Markets Association. Master Repurchase Agreements provide that all transactions under the agreement constitute a single contractual relationship. An event of default by the counterparty allows the early termination of all outstanding transactions under the same agreement and we may offset all outstanding amounts related to the terminated transactions including collateral posted or received. We also have securities purchased under agreements to resell which we transact through the Fixed Income Clearing Corporation (“FICC”). Under the rules of the FICC, all agreements for securities purchased under agreements to resell that are submitted to the FICC for clearing become transactions with the FICC that are subject to FICC clearing rules. In the event of a FICC default, all open positions at the FICC are closed and a net position is calculated.

Fair Value

Fair Value	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value	Fair Value We use fair value measurements for the initial recording of certain assets and liabilities and periodic remeasurement of certain assets and liabilities on a recurring or nonrecurring basis. Fair Value Measurement Fair value measurement guidance defines fair value, establishes a framework for measuring fair value and sets forth disclosures around fair value measurements. This guidance applies whenever other accounting guidance requires or permits assets or liabilities to be measured at fair value. The guidance establishes a three-level fair value hierarchy that prioritizes the inputs into the valuation techniques used to measure fair value. The fair value hierarchy gives the highest priority, Level 1, to measurements based on unadjusted quoted prices in active markets for identical assets or liabilities. The next highest priority, Level 2, is given to measurements of assets and liabilities based on limited observable inputs or observable inputs for similar assets and liabilities. The lowest priority, Level 3, is given to measurements based on unobservable inputs. Recurring Changes in Fair Value The following tables display our assets and liabilities measured in our consolidated balance sheets at fair value on a recurring basis subsequent to initial recognition, including instruments for which we have elected the fair value option. Fair Value Measurements as of December 31, 2017 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Netting Adjustment (1) Estimated Fair Value (Dollars in millions) Recurring fair value measurements: Assets: Trading securities: Mortgage-related securities: Fannie Mae $ — $ 2,905 $ 971 $ — $ 3,876 Other agency — 1,083 35 — 1,118 Alt-A and subprime private-label securities — 259 194 — 453 CMBS — 9 — — 9 Mortgage revenue bonds — — 1 — 1 Non-mortgage-related securities: U.S. Treasury securities 29,222 — — — 29,222 Total trading securities 29,222 4,256 1,201 — 34,679 Available-for-sale securities: Mortgage-related securities: Fannie Mae — 1,911 208 — 2,119 Other agency — 357 — — 357 Alt-A and subprime private-label securities — 1,237 77 — 1,314 CMBS — 15 — — 15 Mortgage revenue bonds — — 671 — 671 Other — 10 357 — 367 Total available-for-sale securities — 3,530 1,313 — 4,843 Mortgage loans — 9,480 1,116 — 10,596 Other assets: Risk management derivatives: Swaps — 4,035 146 — 4,181 Swaptions — 108 — — 108 Other — — 22 — 22 Netting adjustment — — — (4,272 ) (4,272 ) Mortgage commitment derivatives — 131 1 — 132 Total other assets — 4,274 169 (4,272 ) 171 Total assets at fair value $ 29,222 $ 21,540 $ 3,799 $ (4,272 ) $ 50,289 Fair Value Measurements as of December 31, 2017 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Netting Adjustment (1) Estimated Fair Value (Dollars in millions) Liabilities: Long-term debt: Of Fannie Mae: Senior floating $ — $ 7,810 $ 376 $ — $ 8,186 Total of Fannie Mae — 7,810 376 — 8,186 Of consolidated trusts — 29,911 582 — 30,493 Total long-term debt — 37,721 958 — 38,679 Other liabilities: Risk management derivatives: Swaps — 4,721 33 — 4,754 Swaptions — 324 — — 324 Other — — 1 — 1 Netting adjustment — — — (4,979 ) (4,979 ) Mortgage commitment derivatives — 227 1 — 228 Total other liabilities — 5,272 35 (4,979 ) 328 Total liabilities at fair value $ — $ 42,993 $ 993 $ (4,979 ) $ 39,007 Fair Value Measurements as of December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Netting Adjustment (1) Estimated Fair Value (Dollars in millions) Assets: Trading securities: Mortgage-related securities: Fannie Mae $ — $ 3,934 $ 835 $ — $ 4,769 Other agency — 2,058 — — 2,058 Alt-A and subprime private-label securities — 365 271 — 636 CMBS — 761 — — 761 Mortgage revenue bonds — — 21 — 21 Non-mortgage-related securities: U.S. Treasury securities 32,317 — — — 32,317 Total trading securities 32,317 7,118 1,127 — 40,562 Available-for-sale securities: Mortgage-related securities: Fannie Mae — 2,324 230 — 2,554 Other agency — 542 5 — 547 Alt-A and subprime private-label securities — 2,492 217 — 2,709 CMBS — 819 — — 819 Mortgage revenue bonds — — 1,272 — 1,272 Other — 33 429 — 462 Total available-for-sale securities — 6,210 2,153 — 8,363 Mortgage loans — 10,860 1,197 — 12,057 Other assets: Risk management derivatives: Swaps — 4,159 137 — 4,296 Swaptions — 241 — — 241 Other — — 33 — 33 Netting adjustment — — — (4,514 ) (4,514 ) Mortgage commitment derivatives — 619 12 — 631 Total other assets — 5,019 182 (4,514 ) 687 Total assets at fair value $ 32,317 $ 29,207 $ 4,659 $ (4,514 ) $ 61,669 Fair Value Measurements as of December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Netting Adjustment (1) Estimated Fair Value (Dollars in millions) Liabilities: Long-term debt: Of Fannie Mae: Senior floating $ — $ 9,235 $ 347 $ — $ 9,582 Total of Fannie Mae — 9,235 347 — 9,582 Of consolidated trusts — 36,283 241 — 36,524 Total long-term debt — 45,518 588 — 46,106 Other liabilities: Risk management derivatives: Swaps — 6,933 48 — 6,981 Swaptions — 339 — — 339 Other — — 2 — 2 Netting adjustment — — — (6,844 ) (6,844 ) Mortgage commitment derivatives — 649 88 — 737 Total other liabilities — 7,921 138 (6,844 ) 1,215 Total liabilities at fair value $ — $ 53,439 $ 726 $ (6,844 ) $ 47,321 __________ (1) Derivative contracts are reported on a gross basis by level. The netting adjustment represents the effect of the legal right to offset under legally enforceable master netting arrangements to settle with the same counterparty on a net basis, including cash collateral posted and received. The following tables display a reconciliation of all assets and liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3). The tables also display gains and losses due to changes in fair value, including both realized and unrealized gains and losses, recognized in our consolidated statements of operations and comprehensive income for Level 3 assets and liabilities. When assets and liabilities are transferred between levels, we recognize the transfer as of the end of the period. Fair Value Measurements Using Significant Unobservable Inputs (Level 3) For the Year Ended December 31, 2017 Total Gains (Losses) (Realized/Unrealized) Net Unrealized Gains (Losses) Included in Net Income Related to Assets and Liabilities Still Held as of December 31, 2017 (5)(6) Balance, December 31, 2016 Included in Net Income Included in Total Other Comprehensive Income (Loss) (1) Purchases (2) Sales (2) Issues (3) Settlements (3) Transfers out of Level 3 (4) Transfers into Level 3 (4) Balance, December 31, 2017 (Dollars in millions) Trading securities: Mortgage-related: Fannie Mae $ 835 $ 41 $ — $ 64 $ — $ — $ (5 ) $ (991 ) $ 1,027 $ 971 $ 6 Other agency — — — 35 — — — — — 35 — Alt-A and subprime private-label securities 271 15 — — (60 ) — (32 ) — — 194 5 Mortgage revenue bonds 21 3 — — (21 ) — (2 ) — — 1 — Total trading securities $ 1,127 $ 59 (6)(7) $ — $ 99 $ (81 ) $ — $ (39 ) $ (991 ) $ 1,027 $ 1,201 $ 11 Available-for-sale securities: Mortgage-related: Fannie Mae $ 230 $ 2 $ (1 ) $ — $ — $ — $ (9 ) $ (72 ) $ 58 $ 208 $ — Other agency 5 — — — (1 ) — — (4 ) — — — Alt-A and subprime private-label securities 217 54 (53 ) — (105 ) — (36 ) — — 77 — Mortgage revenue bonds 1,272 35 (11 ) — (392 ) — (233 ) — — 671 — Other 429 8 (11 ) — (5 ) — (64 ) — — 357 — Total available-for-sale securities $ 2,153 $ 99 (7)(8) $ (76 ) $ — $ (503 ) $ — $ (342 ) $ (76 ) $ 58 $ 1,313 $ — Mortgage loans $ 1,197 $ 45 (6)(7) $ — $ 5 $ — $ — $ (233 ) $ (70 ) $ 172 $ 1,116 $ 25 Net derivatives 44 111 (6) — — — — (22 ) 6 (5 ) 134 13 Long-term debt: Of Fannie Mae: Senior floating $ (347 ) $ (29 ) (6) $ — $ — $ — $ — $ — $ — $ — $ (376 ) $ (29 ) Of consolidated trusts (241 ) (9 ) (6)(7) — — — (2 ) 66 388 (784 ) (582 ) (11 ) Total long-term debt $ (588 ) $ (38 ) $ — $ — $ — $ (2 ) $ 66 $ 388 $ (784 ) $ (958 ) $ (40 ) Fair Value Measurements Using Significant Unobservable Inputs (Level 3) For the Year Ended December 31, 2016 Total Gains (Losses) (Realized/Unrealized) Net Unrealized Gains (Losses) Included in Net Income Related to Assets and Liabilities Still Held as of December 31, 2016 (5)(6) Balance, December 31, 2015 Included in Net Income Included in Total Other Comprehensive Income (Loss) (1) Purchases (2) Sales (2) Issues (3) Settlements (3) Transfers out of Level 3 (4) Transfers into Level 3 (4) Balance, December 31, 2016 (Dollars in millions) Trading securities: Mortgage-related: Fannie Mae $ — $ — $ — $ — $ — $ — $ (1 ) $ (24 ) $ 860 $ 835 $ — Other agency — — — — — — — (1 ) 1 — — Alt-A and subprime private-label securities 949 (33 ) — — (231 ) — (51 ) (363 ) — 271 (1 ) Mortgage revenue bonds 449 33 — — (448 ) — (13 ) — — 21 (2 ) Total trading securities $ 1,398 $ — (6)(7) $ — $ — $ (679 ) $ — $ (65 ) $ (388 ) $ 861 $ 1,127 $ (3 ) Available-for-sale securities: Mortgage-related: Fannie Mae $ — $ — $ — $ — $ — $ — $ — $ (1 ) $ 231 $ 230 $ — Other agency 4 — — — — — — (4 ) 5 5 — Alt-A and subprime private-label securities 4,322 184 (233 ) — (997 ) — (220 ) (2,839 ) — 217 — Mortgage revenue bonds 2,701 132 (34 ) — (1,129 ) — (398 ) — — 1,272 — Other 1,404 — (12 ) — (605 ) — (74 ) (284 ) — 429 — Total available-for-sale securities $ 8,431 $ 316 (7)(8) $ (279 ) $ — $ (2,731 ) $ — $ (692 ) $ (3,128 ) $ 236 $ 2,153 $ — Mortgage loans $ 1,477 $ 129 (6)(7) $ — $ 36 $ (392 ) $ — $ (255 ) $ (77 ) $ 279 $ 1,197 $ 17 Net derivatives 157 15 (6) — — — (8 ) (122 ) 2 — 44 (132 ) Long-term debt: Of Fannie Mae: Senior floating $ (369 ) $ 22 (6) $ — $ — $ — $ — $ — $ — $ — $ (347 ) $ 22 Of consolidated trusts (496 ) (75 ) (6)(7) — — — (74 ) 378 215 (189 ) (241 ) (9 ) Total long-term debt $ (865 ) $ (53 ) $ — $ — $ — $ (74 ) $ 378 $ 215 $ (189 ) $ (588 ) $ 13 Fair Value Measurements Using Significant Unobservable Inputs (Level 3) For the Year Ended December 31, 2015 Total Gains (Losses) (Realized/Unrealized) Net Unrealized Gains (Losses) Included in Net Income Related to Assets and Liabilities Still Held as of December 31, 2015 (5)(6) Balance, December 31, 2014 Included in Net Income Included in Total Other Comprehensive Income (Loss) (1) Purchases (2) Sales (2) Issues (3) Settlements (3) Transfers out of Level 3 (4) Transfers into Level 3 (4) Balance, December 31, 2015 (Dollars in millions) Trading securities: Mortgage-related: Fannie Mae $ 305 $ (27 ) $ — $ — $ (2 ) $ — $ — $ (278 ) $ 2 $ — $ — Alt-A and subprime private-label securities 1,904 72 — — (878 ) — (133 ) (44 ) 28 949 25 Mortgage revenue bonds 722 (41 ) — — (220 ) — (12 ) — — 449 (33 ) Other 99 4 — — (100 ) — (3 ) — — — — Total trading securities $ 3,030 $ 8 (6)(7) $ — $ — $ (1,200 ) $ — $ (148 ) $ (322 ) $ 30 $ 1,398 $ (8 ) Available-for-sale securities: Mortgage-related: Fannie Mae $ — $ — $ — $ 421 $ (425 ) $ — $ (8 ) $ — $ 12 $ — $ — Other agency 6 — — — — — (1 ) (2 ) 1 4 — Alt-A and subprime private-label securities 8,380 814 (555 ) — (3,079 ) — (1,037 ) (538 ) 337 4,322 — Mortgage revenue bonds 4,023 51 (104 ) — (410 ) — (859 ) — — 2,701 — Other 2,671 (26 ) (2 ) — (1,012 ) — (227 ) — — 1,404 — Total available-for-sale securities $ 15,080 $ 839 (7)(8) $ (661 ) $ 421 $ (4,926 ) $ — $ (2,132 ) $ (540 ) $ 350 $ 8,431 $ — Mortgage loans $ 1,833 $ 57 (6)(7) $ — $ 5 $ — $ — $ (350 ) $ (377 ) $ 309 $ 1,477 $ (20 ) Net derivatives 45 (55 ) (6) — — — (4 ) 169 (7 ) 9 157 (2 ) Long-term debt: Of Fannie Mae: Senior floating $ (363 ) $ (6 ) (6) $ — $ — $ — $ — $ — $ — $ — $ (369 ) $ (6 ) Of consolidated trusts (527 ) (9 ) (6)(7) — — — (66 ) 57 228 (179 ) (496 ) 17 Total long-term debt $ (890 ) $ (15 ) $ — $ — $ — $ (66 ) $ 57 $ 228 $ (179 ) $ (865 ) $ 11 __________ (1) Losses included in other comprehensive income are included in “Changes in unrealized gains on available-for-sale securities, net of reclassification adjustments and taxes” in our consolidated statements of operations and comprehensive income. (2) Purchases and sales include activity related to the consolidation and deconsolidation of assets of securitization trusts. (3) Issues and settlements include activity related to the consolidation and deconsolidation of liabilities of securitization trusts. (4) Transfers into and out of Level 3 consisted primarily of Fannie Mae securities backed by private-label mortgage-related securities. Prices for these securities are based on inputs that were not readily observable. Transfers out of Level 3 also occurred for private-label mortgage-related securities backed by Alt-A loans and subprime loans. Prices for these securities were available from multiple third-party vendors and demonstrated an increased and sustained level of observability over time. (5) Amount represents temporary changes in fair value. Amortization, accretion and OTTI are not considered unrealized and are not included in this amount. (6) Gains (losses) are included in “Fair value losses, net” in our consolidated statements of operations and comprehensive income. (7) Gains (losses) are included in “Net interest income” in our consolidated statements of operations and comprehensive income. (8) Gains (losses) are included in “Investment gains, net” in our consolidated statements of operations and comprehensive income. The following tables display valuation techniques and the range and the weighted average of significant unobservable inputs for our Level 3 assets and liabilities measured at fair value on a recurring basis. Fair Value Measurements as of December 31, 2017 Fair Value Significant Valuation Techniques Significant Unobservable Inputs (1) Range (1) Weighted - Average (1) (Dollars in millions) Recurring fair value measurements: Trading securities: Mortgage-related securities: Agency (2) $ 971 Single Vendor Prepayment Speed (%) 0.0 - 177.0 160.0 Spreads (bps) 51.5 - 375.0 200.1 35 Various Total agency 1,006 Alt-A and subprime private-label securities 154 Consensus 40 Various Total Alt-A and subprime private-label securities 194 Mortgage revenue bonds 1 Various Total trading securities $ 1,201 Fair Value Measurements as of December 31, 2017 Fair Value Significant Valuation Techniques Significant Unobservable Inputs (1) Range (1) Weighted - Average (1) (Dollars in millions) Available-for-sale securities: Mortgage-related securities: Agency (2) $ 112 Single Vendor Prepayment Speed (%) 0.0 - 175.7 147.1 Spreads (bps) 150.0 - 210.0 182.3 96 Various Total agency 208 Alt-A and subprime private-label securities 77 Various Mortgage revenue bonds 475 Single Vendor Spreads (bps) (17.0 ) - 248.0 39.0 196 Various Total mortgage revenue bonds 671 Other 325 Discounted Cash Flow Prepayment Speed (%) 1.6 - 2.5 2.5 Severity (%) 50.0 - 88.0 86.6 Spreads (bps) 84.8 - 607.0 577.9 32 Various Total other 357 Total available-for-sale securities $ 1,313 Mortgage loans: Single-family $ 406 Build-Up 344 Consensus 208 Various Total single-family 958 Multifamily 155 Build-Up Spreads (bps) 29.0 - 267.2 105.8 3 Various Total multifamily $ 158 Total mortgage loans $ 1,116 Net derivatives $ 113 Dealer Mark 21 Various Total net derivatives $ 134 Long-term debt: Of Fannie Mae: Senior floating $ (376 ) Discounted Cash Flow Of consolidated trusts (3) (401 ) Discounted Cash Flow Default Rate (%) 1.6 - 6.3 4.6 Prepayment Speed (%) 5.4 - 100.0 98.9 Severity (%) 28.0 - 95.0 71.5 Spreads (bps) 42.0 - 228.3 78.7 (181 ) Various Total of consolidated trusts (582 ) Total long-term debt $ (958 ) Fair Value Measurements as of December 31, 2016 Fair Value Significant Valuation Techniques Significant Unobservable Inputs (1) Range (1) Weighted - Average (1) (Dollars in millions) Recurring fair value measurements: Trading securities: Mortgage-related securities: Agency (2) $ 809 Consensus 26 Various Total agency 835 Alt-A and subprime private-label securities 232 Consensus Default Rate (%) 0.4 - 10.9 8.2 Prepayment Speed (%) 4.3 - 7.4 6.6 Severity (%) 71.0 - 95.0 88.9 Spreads (bps) 244.6 - 253.9 251.5 39 Consensus Total Alt-A and subprime private-label securities 271 Mortgage revenue bonds 19 Discounted Cash Flow Spreads (bps) 13.0 - 268.2 252.2 2 Various Total mortgage revenue bonds 21 Total trading securities $ 1,127 Available-for-sale securities: Mortgage-related securities: Agency (2) $ 129 Single Vendor Prepayment Speed (%) 124.8 - 165.5 142.4 Spreads (bps) 175.0 - 210.0 182.5 72 Consensus 34 Various Total agency 235 Alt-A and subprime private-label securities 93 Single Vendor Default Rate (%) 2.5 - 8.0 3.8 Prepayment Speed (%) 3.0 - 11.0 4.9 Severity (%) 38.0 - 80.0 48.1 Spreads (bps) 266.1 - 306.8 297.1 45 Discounted Cash Flow Spreads (bps) 361.0 - 450.0 406.0 79 Various Total Alt-A and subprime private-label securities 217 Mortgage revenue bonds 684 Single Vendor Spreads (bps) (16.8 ) - 336.9 44.3 126 Single Vendor 435 Discounted Cash Flow Spreads (bps) (16.8 ) - 391.1 260.0 27 Various Total mortgage revenue bonds 1,272 Other 47 Consensus Default Rate (%) 0.5 - 3.5 3.5 Prepayment Speed (%) 2.5 - 6.0 2.5 Severity (%) 20.0 - 88.0 87.5 Spreads (bps) 221.6 - 300.2 237.7 348 Discounted Cash Flow Default Rate (%) 2.3 2.3 Prepayment Speed (%) 0.5 0.5 Severity (%) 95.0 95.0 Spreads (bps) 190.0 - 450.0 449.1 34 Various Total other 429 Total available-for-sale securities $ 2,153 Fair Value Measurements as of December 31, 2016 Fair Value Significant Valuation Techniques Significant Unobservable Inputs (1) Range (1) Weighted - Average (1) (Dollars in millions) Mortgage loans: Single-family $ 516 Build-Up 300 Consensus 218 Various Total single-family 1,034 Multifamily 163 Build-Up Spreads (bps) 55.0 - 305.2 140.2 Total mortgage loans $ 1,197 Net derivatives $ 10 Internal Model 89 Dealer Mark 21 Discounted Cash Flow (76 ) Various Total net derivatives $ 44 Long-term debt: Of Fannie Mae: Senior floating $ (347 ) Discounted Cash Flow Of consolidated trusts (241 ) Various Total long-term debt $ (588 ) _________ (1) Valuation techniques for which no unobservable inputs are disclosed generally reflect the use of third-party pricing services or dealers, and the range of unobservable inputs applied by these sources is not readily available or cannot be reasonably estimated. Where we have disclosed unobservable inputs for consensus and single vendor techniques, those inputs are based on our validations performed at the security level using discounted cash flows. The prepayment speed used for available-for-sale agency securities is the Public Securities Association (“PSA”) prepayment speed, which can be greater than 100%. For all other securities, the Conditional Prepayment Rate (“CPR”) is used as the prepayment speed, which can be between 0% and 100%. (2) Includes Fannie Mae and Freddie Mac securities. (3) Includes instruments for which the prepayment speed represents the estimated annualized rate of prepayment after all prepayment penalty provisions have expired and also instruments for which prepayment speed represents the estimated rate of prepayment over the remaining life of the instrument. In our consolidated balance sheets certain assets and liabilities are measured at fair value on a nonrecurring basis; that is, the instruments are not measured at fair value on an ongoing basis but are subject to fair value adjustments in certain circumstances (for example, when we evaluate loans for impairment). We did not have any Level 1 assets or liabilities that were measured at fair value on a nonrecurring basis as of December 31, 2017 or December 31, 2016 . We held $14 million and $250 million in Level 2 assets, comprised of mortgage loans held for sale, and no Level 2 liabilities that were measured at fair value on a nonrecurring basis as of December 31, 2017 and December 31, 2016 , respectively. The following table displays valuation techniques for our Level 3 assets measured at fair value on a nonrecurring basis. The significant unobservable inputs related to these techniques primarily relate to collateral dependent valuations. The related ranges and weighted averages are not meaningful when aggregated as they vary significantly from property to property. Fair Value Measurements as of December 31, Valuation Techniques 2017 2016 (Dollars in millions) Nonrecurring fair value measurements: Mortgage loans held for sale, at lower of cost or fair value Consensus $ 1,113 $ 1,025 Single Vendor 1,880 54 Various — 9 Total mortgage loans held for sale, at lower of cost or fair value 2,993 1,088 Single-family mortgage loans held for investment, at amortized cost Internal Model 1,623 2,816 Multifamily mortgage loans held for investment, at amortized cost Broker Price Opinions 28 25 Asset Manager Estimate 163 170 Various 4 3 Total multifamily mortgage loans held for investment, at amortized cost 195 198 Acquired property, net: (1) Single-family Accepted Offers 218 340 Appraisals 438 571 Walk Forwards 222 306 Internal Model 319 476 Various 113 99 Total single-family 1,310 1,792 Multifamily Various 19 — Other assets Various 2 12 Total nonrecurring assets at fair value $ 6,142 $ 5,906 _________ (1) The most commonly used techniques in our valuation of acquired property are proprietary home price model and third-party valuations (both current and walk forward). Based on the number of properties measured as of December 31, 2017 , these methodologies comprised approximately 77% of our valuations, while accepted offers comprised approximately 18% of our valuations. Based on the number of properties measured as of December 31, 2016 , these methodologies comprised approximately 75% of our valuations, while accepted offers comprised approximately 19% of our valuations. We use valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs. The following is a description of the valuation techniques we use for fair value measurement and disclosure as well as our basis for classifying these measurements as Level 1, Level 2 or Level 3 of the valuation hierarchy in more specific situations. Instruments Valuation Techniques Classification U.S Treasury Securities We classify securities whose values are based on quoted market prices in active markets for identical assets as Level 1 of the valuation hierarchy. Level 1 Trading Securities and Available-for-Sale Securities We classify securities in active markets as Level 2 of the valuation hierarchy if quoted market prices in active markets for identical assets are not available. For all valuation techniques used for securities where there is limited activity or less transparency around these inputs to the valuation, these securities are classified as Level 3 of the valuation hierarchy. Single Vendor: Uses one vendor price to estimate fair value. We generally validate these observations of fair value through the use of a discounted cash flow technique whose unobservable inputs (for example, default rates) are disclosed in the table above. Dealer Mark: Uses one dealer price to estimate fair value. We generally validate these observations of fair value through the use of a discounted cash flow technique whose unobservable inputs (for example, default rates) are disclosed in the table above. Consensus: Uses an average of two or more vendor prices for similar securities. We generally validate these observations of fair value through the use of a discounted cash flow technique whose unobservable inputs (for example, default rates) are disclosed in the table above. Level 2 and 3 Discounted Cash Flow: In the absence of prices provided by third-party pricing services supported by observable market data, we estimate the fair value of a portion of our securities using a discounted cash flow technique that uses inputs such as default rates, prepayment speeds, loss severity and spreads based on market assumptions where available. For private-label securities, an increase in unobservable prepayment speeds in isolation would generally result in an increase in fair value, and an increase in unobservable spreads, severity rates or default rates in isolation would generally result in a decrease in fair value. For mortgage revenue bonds classified as Level 3 of the valuation hierarchy, an increase in unobservable spreads would result in a decrease in fair value. Although the sensitivities of the fair value of our recurring Level 3 securities of the valuation hierarchy to various unobservable inputs are discussed above in isolation, interrelationships exist among these inputs such that a change in one unobservable input typically results in a change to one or more of the other inputs. Mortgage Loans Held for Investment Build-up: We derive the fair value of performing mortgage loans using a build-up valuation technique starting with the base value for our Fannie Mae MBS with similar characteristics and then add or subtract the fair value of the associated guaranty asset, guaranty obligation (“GO”) and master servicing arrangement. We set the GO equal to the estimated fair value we would receive if we were to issue our guaranty to an unrelated party in a stand-alone arm’s length transaction at the measurement date. The fair value of the GO is estimated based on our current guaranty pricing for loans underwritten after 2008 and our internal valuation models considering management’s best estimate of key loan characteristics for loans underwritten before 2008. Our performing loans are generally classified as Level 2 of the valuation hierarchy to the extent that significant inputs are observable. To the extent that unobservable inputs are significant, the loans are classified as Level 3 of the valuation hierarchy. Level 2 and 3 Consensus: Calculated through the extrapolation of indicative sample bids obtained from multiple active market participants plus the estimated value of any applicable mortgage insurance, the estimated fair value using the Consensus method represents an estimate of the prices we would receive if we were to sell these single-family nonperforming and certain reperforming loans in the whole-loan market. The fair value of any mortgage insurance is estimated by taking the loan level coverage and adjusting it by the expected claims paying ability of the associated mortgage insurer. These loans are classified as Level 3 of the valuation hierarchy because significant inputs are unobservable. We estimate the fair value for a portion of our senior-subordinated trust structures using the average of two or more vendor prices at the security level as a proxy for estimating loan fair value. These loans are classified as Level 3 of the valuation hierarchy because significant inputs are unobservable. Single Vendor: We estimate the fair value of our reverse mortgages using the single vendor valuation technique. Internal Model: The internal model used in this process applies one of following two approaches when valuing the collateral depending on the historical accuracy of the two approaches. (1) The comparable foreclosed property sales approach is used in the majority of the internal model valuations. The comparable foreclosed property sales approach uses various factors such as geographic distance, transaction time and the value difference. (2) The median Metropolitan Statistical Area (“MSA”) approach is based on the median of all the foreclosure sales of REOs in a specific MSA or state when there is not enough REO sales in a specific MSA. These loans are classified as Level 3 of the valuation hierarchy because significant inputs are unobservable. Instruments Valuation Techniques Classification Mortgage Loans Held for Investment Appraisals: Uses appraisals to estimate the fair value for a portion of our multifamily loans based on either estimated replacement cost, the present value of future cash flows, or sales of similar properties. Significant unobservable inputs include estimated replacement or construction costs, property net operating income, capitalization rates, and adjustments made to sales of comparable properties based on characteristics such as financing, conditions of sale, and physical characteristics of the property. Broker Price Opinion (“BPO”): Uses BPO to estimate the fair value for a portion of our multifamily loans. This technique uses both current property value and the property value adjusted for stabilization and market conditions. The unobservable inputs used in this technique are property net operating income and market capitalization rates to estimate property value. Asset Manager Estimate (“AME”): This technique uses the net operating income and tax assessments of the specific property as well as MSA-specific market capitalization rates and average per unit sales values to estimate property fair value. Level 2 and 3 An increase in prepayment speeds in isolation would generally result in an increase in the fair value of our mortgage loans classified as Level 3 of the valuation hierarchy, and an increase in severity rates, default rates or spreads in isolation would generally result in a decrease in fair value. Although the sensitivities of the fair value of mortgage loans classified as Level 3 of the valuation hierarchy to various unobservable inputs are discussed above in isolation, interrelationships exist among these inputs such that a change in one unobservable input typically results in a change to one or more of the other inputs. Acquired Property, Net and Other Assets Single-family acquired property valuation techniques Appraisal: An appraisal is an estimate based on recent historical data of the value of a specific property by a certified or licensed appraiser. Adjustments are made for differences between comparable properties for unobservable inputs such as square footage, location, and condition of the property. Broker Price Opinion: This technique provides an estimate of what the property is worth based upon a real estate broker’s use of specific market research and a sales comparison approach that is similar to the appraisal process. This information, all of which is unobservable, is used along with recent and pending sales and current listings of similar properties to arrive at an estimate of value. Level 3 Appraisal and Broker Price Opinion Walk Forwards (“Walk Forwards”): We use these techniques to adjust appraisal and broker price opinion valuations for changing market conditions by applying a walk forward factor based on local price movements since the time the third-party value was obtained. Internal Model: We use an internal model to estimate fair value for distressed properties. The valuation methodology and inputs used are described under “Mortgage Loans Held for Investment.” Multifamily acquired property valuation techniques Appraisals: We use this method to estimate property values for distressed properties. The valuation methodology and inputs used are described under “Mortgage Loans Held for Investment.” Broker Price Opinions: We use this method to estimate property values for distressed properties. The valuation methodology and inputs used are described under “Mortgage Loans Held for Investment.” Asset Manager Estimate (“AME”): We use this method to estimate property values for distressed properties. The valuation methodology and inputs used are described under “Mortgage Loans Held for Investment.” Derivatives Assets and Liabilities (collectively “Derivatives”) The valuation process for the majority of our risk management derivatives uses observable market data provided by third-party sources, resulting in Level 2 classification of the valuation hierarchy. Internal Model: We use internal models to value interest rate swaps which are valued by referencing yield curves derived from observable interest rates and spreads to project and discount swap cash flows to present value. Option-based derivatives use an internal model that projects the probability of various levels of interest rates by referencing swaption volatilities provided by market makers/dealers. The projected cash flows of the underlying swaps of these option-based derivatives are discounted to present value using yield curves derived from observable interest rates and spreads. Dealer Mark: Certain highly complex structured swaps primarily use a single dealer mark due to lack of transparency in the market and may be modeled using observable interest rates and volatility levels as well as significant unobservable assumptions, resulting in Level 3 classification of the valuation hierarchy. Mortgage commitment deriva

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies We are party to various types of legal actions and proceedings, including actions brought on behalf of various classes of claimants. We also are subject to regulatory examinations, inquiries and investigations, and other information gathering requests. In some of the matters, indeterminate amounts are sought. Modern pleading practice in the U.S. permits considerable variation in the assertion of monetary damages or other relief. Jurisdictions may permit claimants not to specify the monetary damages sought or may permit claimants to state only that the amount sought is sufficient to invoke the jurisdiction of the trial court. This variability in pleadings, together with our and our counsel’s actual experience in litigating or settling claims, leads us to conclude that the monetary relief that may be sought by plaintiffs bears little relevance to the merits or disposition value of claims. On a quarterly basis, we review relevant information about all pending legal actions and proceedings for the purpose of evaluating and revising our contingencies, accruals and disclosures. We have substantial and valid defenses to the claims in the proceedings described below and intend to defend these matters vigorously. However, legal actions and proceedings of all types are subject to many uncertain factors that generally cannot be predicted with assurance. Accordingly, the outcome of any given matter and the amount or range of potential loss at particular points in time is frequently difficult to ascertain. Uncertainties can include how fact finders will evaluate documentary evidence and the credibility and effectiveness of witness testimony, and how courts will apply the law. Disposition valuations are also subject to the uncertainty of how opposing parties and their counsel may view the evidence and applicable law. We establish an accrual for matters when a loss is probable and we can reasonably estimate the amount of such loss. For legal actions or proceedings where the likelihood of a loss is not probable or cannot be reasonably estimated, we do not establish an accrual. We are often unable to estimate the possible losses or ranges of losses, particularly for proceedings that are in their early stages of development, where plaintiffs seek indeterminate or unspecified damages, where there may be novel or unsettled legal questions relevant to the proceedings, or where settlement negotiations have not occurred or progressed. Given the uncertainties involved in any action or proceeding, regardless of whether we have established an accrual, the ultimate resolution of certain of these matters may be material to our operating results for a particular period, depending on, among other factors, the size of the loss or liability imposed and the level of our net income or loss for that period. In addition to the matters specifically described in this report, we are involved in a number of legal and regulatory proceedings that arise in the ordinary course of business that we do not expect will have a material impact on our business or financial condition. We have also advanced fees and expenses of certain current and former officers and directors in connection with various legal proceedings pursuant to our bylaws and indemnification agreements. Senior Preferred Stock Purchase Agreements Litigation A consolidated class action and two non-class action lawsuits filed by Fannie Mae and Freddie Mac shareholders are pending in the U.S. District Court for the District of Columbia against us, FHFA as our conservator, and Freddie Mac that challenge the August 2012 amendment to each company’s senior preferred stock purchase agreement with Treasury. In the consolidated class action (“ In re Fannie Mae/Freddie Mac Senior Preferred Stock Purchase Agreement Class Action Litigations ”), plaintiffs filed an amended complaint on November 1, 2017 that alleges the net worth sweep dividend provisions of the senior preferred stock that were implemented pursuant to the August 2012 amendments nullified certain of the shareholders’ rights, particularly the right to receive dividends. Plaintiffs allege claims for breach of contract, breach of the implied covenant of good faith and fair dealing, breach of fiduciary duties, and violations of Delaware and Virginia corporate law against us, FHFA and Freddie Mac, and breach of fiduciary duties claims derivatively on our and Freddie Mac’s behalf against FHFA. Plaintiffs seek to represent several classes of preferred and/or common shareholders of Fannie Mae and/or Freddie Mac who held stock as of the public announcement of the August 2012 amendments. Plaintiffs seek unspecified damages, equitable and injunctive relief, and costs and expenses, including attorneys’ fees. The defendants moved to dismiss the amended complaint on January 10, 2018. In the two non-class action suits, Arrowood Indemnity Company v. Fannie Mae and Fairholme Funds v. FHFA , the plaintiffs, Fannie Mae and Freddie Mac preferred shareholders, filed amended complaints on November 1, 2017 against us, FHFA as our conservator, the Director of FHFA (in his official capacity) and Freddie Mac alleging that the net worth sweep dividend provisions nullified certain rights of the preferred shareholders, particularly the right to receive dividends, and exceeded FHFA’s statutory authority. Plaintiffs bring claims for breach of contract, breach of the implied covenant of good faith and fair dealing, breach of fiduciary duties and violations of Delaware and Virginia corporate law. They also assert claims for violation of the Administrative Procedure Act against FHFA. Plaintiffs seek damages, equitable and injunctive relief, and costs and expenses, including attorneys’ fees. The defendants moved to dismiss both amended complaints on January 10, 2018. Plaintiffs in all three cases filed the amended complaints after the U.S. Court of Appeals for the D.C. Circuit issued a ruling on February 21, 2017 that affirmed in part and reversed in part the district court’s dismissal of the plaintiffs’ original complaints. In addition to filing the amended complaints, plaintiffs also filed petitions for certiorari with the United States Supreme Court on October 16, 2017 seeking review of the Court of Appeals’ rulings that plaintiffs could not pursue claims alleging violation of the Administrative Procedure Act and no conflict existed in allowing FHFA to decide whether to pursue derivative claims on behalf of Fannie Mae and Freddie Mac while they are in conservatorship. On August 2, 2017, shareholder David J. Voacolo filed a lawsuit, Voacolo v. Fannie Mae , in the U.S. District Court for the District of New Jersey against Fannie Mae and the United States alleging that the net worth sweep dividend provisions of the senior preferred stock that were implemented pursuant to the August 2012 amendments to the senior preferred stock purchase agreements were a violation of due process and an illegal exaction. Plaintiff seeks damages only. Given the stage of these lawsuits, the substantial and novel legal questions that remain, and our substantial defenses, we are currently unable to estimate the reasonably possible loss or range of loss arising from this litigation. Unconditional Purchase and Lease Commitments We have unconditional commitments related to the purchase of loans and mortgage-related securities. These include both on- and off-balance sheet commitments. A portion of these have been recorded as derivatives in our consolidated balance sheets. We lease certain premises and equipment under agreements that expire at various dates through 2033 . Some of these leases provide for payment by the lessee of property taxes, insurance premiums, cost of maintenance and other costs. Rental expenses for operating leases were $61 million , $50 million and $47 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. The following table summarizes by remaining maturity, non-cancelable future commitments related to loan and mortgage purchases, operating leases and other agreements. As of December 31, 2017 Loans and Mortgage-Related Securities (1) Operating Leases (2) Other (3) (Dollars in millions) 2018 $ 73,130 $ 41 $ 98 2019 — 48 57 2020 — 56 73 2021 — 56 14 2022 — 58 1 Thereafter — 609 — Total $ 73,130 $ 868 $ 243 __________ (1) Primarily includes $72.7 billion that has been accounted for as mortgage commitment derivatives. (2) Includes amounts related to office buildings and equipment leases. (3) Includes purchase commitments for certain telecommunications services, computer software and services, and other agreements and commitments.

Selected Quarterly Financial In

Selected Quarterly Financial Information (Unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Information (Unaudited)	Selected Quarterly Financial Information (Unaudited) The consolidated statements of operations for the quarterly periods in 2017 and 2016 are unaudited and in the opinion of management include all adjustments, consisting of normal recurring adjustments, necessary for a fair presentation of our consolidated statements of operations. Certain prior period amounts have been reclassified to conform to the current period presentation. The operating results for the interim periods are not necessarily indicative of the operating results to be expected for a full year or for other interim periods. For the 2017 Quarter Ended March 31 June 30 September 30 December 31 (Dollars and shares in millions, except per share amounts) Interest income: Trading securities $ 142 $ 176 $ 195 $ 193 Available-for-sale securities 101 91 77 66 Mortgage loans 27,047 27,011 27,047 27,214 Other 94 115 142 145 Total interest income 27,384 27,393 27,461 27,618 Interest expense: Short-term debt (44 ) (57 ) (72 ) (77 ) Long-term debt (21,994 ) (22,334 ) (22,115 ) (22,430 ) Total interest expense (22,038 ) (22,391 ) (22,187 ) (22,507 ) Net interest income 5,346 5,002 5,274 5,111 Benefit (provision) for credit losses 396 1,267 (182 ) 560 Net interest income after benefit (provision) for credit losses 5,742 6,269 5,092 5,671 Investment gains (losses), net (9 ) 385 313 833 Fair value gains (losses), net (40 ) (691 ) (289 ) (191 ) Fee and other income 249 353 1,194 431 Non-interest income 200 47 1,218 1,073 Administrative expenses: Salaries and employee benefits (344 ) (332 ) (331 ) (321 ) Professional services (229 ) (234 ) (218 ) (252 ) Other administrative expenses (111 ) (120 ) (115 ) (130 ) Total administrative expenses (684 ) (686 ) (664 ) (703 ) Foreclosed property expense (217 ) (34 ) (140 ) (130 ) TCCA fees (503 ) (518 ) (531 ) (544 ) Other expenses, net (382 ) (291 ) (427 ) (411 ) Total expenses (1,786 ) (1,529 ) (1,762 ) (1,788 ) Income before federal income taxes 4,156 4,787 4,548 4,956 Provision for federal income taxes (1,383 ) (1,587 ) (1,525 ) (11,489 ) Net income (loss) attributable to Fannie Mae 2,773 3,200 3,023 (6,533 ) Dividends distributed or available for distribution to senior preferred stockholder (1) (2,779 ) (3,117 ) (3,048 ) — Net income (loss) attributable to common stockholders $ (6 ) $ 83 $ (25 ) $ (6,533 ) Earnings (loss) per share: Basic $ 0.00 $ 0.01 $ 0.00 $ (1.13 ) Diluted 0.00 0.01 0.00 (1.13 ) Weighted-average common shares outstanding: Basic 5,762 5,762 5,762 5,762 Diluted 5,762 5,893 5,762 5,762 For the 2016 Quarter Ended March 31 June 30 September 30 December 31 (Dollars and shares in millions, except per share amounts) Interest income: Trading securities $ 120 $ 128 $ 140 $ 128 Available-for-sale securities 203 170 134 113 Mortgage loans 26,961 26,256 25,611 25,814 Other 48 46 66 83 Total interest income 27,332 26,600 25,951 26,138 Interest expense: Short-term debt (51 ) (57 ) (56 ) (42 ) Long-term debt (22,512 ) (21,257 ) (20,460 ) (20,291 ) Total interest expense (22,563 ) (21,314 ) (20,516 ) (20,333 ) Net interest income 4,769 5,286 5,435 5,805 Benefit (provision) for credit losses 1,184 1,601 673 (1,303 ) Net interest income after benefit (provision) for credit losses 5,953 6,887 6,108 4,502 Investment gains, net 69 398 467 322 Fair value gains (losses), net (2,813 ) (1,667 ) (491 ) 3,890 Fee and other income 203 174 175 414 Non-interest income (loss) (2,541 ) (1,095 ) 151 4,626 Administrative expenses: Salaries and employee benefits (364 ) (331 ) (322 ) (319 ) Professional services (215 ) (232 ) (237 ) (271 ) Other administrative expenses (109 ) (115 ) (102 ) (124 ) Total administrative expenses (688 ) (678 ) (661 ) (714 ) Foreclosed property expense (334 ) (63 ) (110 ) (137 ) TCCA fees (440 ) (453 ) (465 ) (487 ) Other expenses, net (264 ) (254 ) (300 ) (210 ) Total expenses (1,726 ) (1,448 ) (1,536 ) (1,548 ) Income before federal income taxes 1,686 4,344 4,723 7,580 Provision for federal income taxes (550 ) (1,398 ) (1,527 ) (2,545 ) Net income attributable to Fannie Mae 1,136 2,946 3,196 5,035 Dividends distributed or available for distribution to senior preferred stockholder (919 ) (2,869 ) (2,977 ) (5,471 ) Net income (loss) attributable to common stockholders (Note 11) $ 217 $ 77 $ 219 $ (436 ) Earnings (loss) per share: Basic $ 0.04 $ 0.01 $ 0.04 $ (0.08 ) Diluted 0.04 0.01 0.04 (0.08 ) Weighted-average common shares outstanding: Basic 5,762 5,762 5,762 5,762 Diluted 5,893 5,893 5,893 5,762 __________ (1) Subsequent to the filing of our quarterly report on Form 10-Q for the quarter ended September 30, 2017 on November 2, 2017, the dividend provisions of our senior preferred stock were amended. As a result, the amount available for distribution as of September 30, 2017 was not the amount ultimately distributed upon payment of our fourth quarter 2017 dividend. See “ Note 11, Equity (Deficit) ” for further information regarding the changes to the dividend provisions of our senior preferred stock and the dividends we paid on the senior preferred stock during 2017.

Summary of Significant Accoun26

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Segment Reporting, Policy [Policy Text Block]	We have two reportable business segments: Single-Family and Multifamily. The Single-Family business operates in the secondary mortgage market relating to loans secured by properties containing four or fewer residential dwelling units. The Multifamily business operates in the secondary mortgage market relating primarily to loans secured by properties containing five or more residential units. We describe the management reporting and allocation process used to generate our segment results in “ Note 10, Segment Reporting .” We have two reportable business segments: Single-Family and Multifamily. Our CEO is the chief operating decision maker and allocates resources and assesses performance based on these two business segments. Results of our two business segments are intended to reflect each segment as if it were a stand-alone business. The sum of the results for our two business segments equals our consolidated results of operations.
Basis of Presentation [Policy Text Block]	Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). To conform to our current period presentation, we have reclassified certain amounts reported in our prior periods’ consolidated financial statements.
Single-Family Guaranty Fees 10 Basis Points Increase due to the Temporary Payroll Tax Cut Continuation Act of 2011 Provision [Policy Text Block]	Effective April 1, 2012, the guaranty fee on all single-family residential mortgages delivered to Fannie Mae on or after that date was increased by 10 basis points. FHFA and Treasury have advised us to remit this fee increase to Treasury with respect to all loans acquired by us on or after April 1, 2012 and before January 1, 2022, and to continue to remit these amounts to Treasury on and after January 1, 2022 with respect to loans we acquired before this date until those loans are paid off or otherwise liquidated. The resulting fee revenue and expense are recorded in “Mortgage loans interest income” and “TCCA fees,” respectively, in our consolidated statements of operations and comprehensive income.
Use of Estimates, Policy [Policy Text Block]	Use of Estimates Preparing consolidated financial statements in accordance with GAAP requires management to make estimates and assumptions that affect our reported amounts of assets and liabilities, and disclosure of contingent assets and liabilities as of the dates of our consolidated financial statements, as well as our reported amounts of revenues and expenses during the reporting periods. Management has made significant estimates in a variety of areas including, but not limited to, valuation of certain financial instruments, and allowance for loan losses. Actual results could be different from these estimates.
Consolidations, Policy [Policy Text Block]	Principles of Consolidation Our consolidated financial statements include our accounts as well as the accounts of the other entities in which we have a controlling financial interest. All intercompany balances and transactions have been eliminated. The typical condition for a controlling financial interest is ownership of a majority of the voting interests of an entity. A controlling financial interest may also exist in entities through arrangements that do not involve voting interests, such as a VIE. We have interests in various entities that are considered to be VIEs. The primary types of entities are securitization trusts guaranteed by us via lender swap and portfolio securitization transactions and mortgage-backed trusts that were not created by us, as well as housing partnerships that are established to finance the acquisition, construction, development or rehabilitation of affordable multifamily and single-family housing. These interests include investments in securities issued by VIEs, such as Fannie Mae MBS created pursuant to our securitization transactions and our guaranty to the entity. We consolidate the substantial majority of our single-class securitization trusts because our role as guarantor and master servicer provides us with the power to direct matters (primarily the servicing of mortgage loans) that impact the credit risk to which we are exposed. In contrast, we do not consolidate single-class securitization trusts when other organizations have the power to direct these activities. Unconsolidated VIEs We do not consolidate VIEs when we are not deemed to be the primary beneficiary.
Consolidation, Variable Interest Entity, Policy [Policy Text Block]	VIE Assessment We have interests in various entities that are considered VIEs. A VIE is an entity (1) that has total equity at risk that is not sufficient to finance its activities without additional subordinated financial support from other entities, (2) where the group of equity holders does not have the power to direct the activities of the entity that most significantly impact the entity’s economic performance, or the obligation to absorb the entity’s expected losses or the right to receive the entity’s expected residual returns, or both, or (3) where the voting rights of some investors are not proportional to their obligations to absorb the expected losses of the entity, their rights to receive the expected residual returns of the entity, or both, and substantially all of the entity’s activities either involve or are conducted on behalf of an investor that has disproportionately few voting rights. We determine if an entity is a VIE by performing a qualitative analysis, which requires certain subjective decisions including, but not limited to, the design of the entity, the variability that the entity was designed to create and pass along to its interest holders, the rights of the parties and the purpose of the arrangement. If we cannot conclude after a qualitative analysis whether an entity is a VIE, we perform a quantitative analysis. The primary types of VIE entities with which we are involved are securitization trusts guaranteed by us via lender swap and portfolio securitization transactions, limited partnership investments in low-income housing tax credit (“LIHTC”) and other housing partnerships, as well as mortgage and asset-backed trusts that were not created by us. Primary Beneficiary Determination If an entity is a VIE, we consider whether our variable interest in that entity causes us to be the primary beneficiary. We are deemed to be the primary beneficiary of a VIE when we have both (1) the power to direct the activities of the VIE that most significantly impact the entity’s economic performance, and (2) exposure to benefits and/or losses that could potentially be significant to the entity. The primary beneficiary of the VIE is required to consolidate and account for the assets, liabilities, and noncontrolling interests of the VIE in its consolidated financial statements. The assessment of which party has the power to direct the activities of the VIE may require significant management judgment when (1) more than one party has power or (2) more than one party is involved in the design of the VIE but no party has the power to direct the ongoing activities that could be significant. We continually assess whether we are the primary beneficiary of the VIEs with which we are involved and therefore may consolidate or deconsolidate a VIE through the duration of our involvement. Examples of certain events that may change whether or not we consolidate the VIE include a change in the design of the entity or a change in our ownership in the entity such that we no longer hold substantially all of the certificates issued by a multi-class resecuritization trust. Measurement of Consolidated Assets and Liabilities When we are the transferor of assets into a VIE that we consolidate at the time of the transfer, we continue to recognize the assets and liabilities of the VIE at the amounts that they would have been recognized if we had not transferred them, and no gain or loss is recognized. For all other VIEs that we consolidate (that is, those for which we are not the transferor), we recognize the assets and liabilities of the VIE in our consolidated financial statements at fair value, and we recognize a gain or loss for the difference between (1) the fair value of the consideration paid, fair value of noncontrolling interests and the reported amount of any previously held interests, and (2) the net amount of the fair value of the assets and liabilities consolidated. However, for the securitization trusts established under our lender swap program, no gain or loss is recognized if the trust is consolidated at formation as there is no difference in the respective fair value of (1) and (2) above. We record gains or losses that are associated with the consolidation of VIEs as a component of “Investment gains, net” in our consolidated statements of operations and comprehensive income . If we cease to be deemed the primary beneficiary of a VIE, we deconsolidate the VIE. We use fair value to measure the initial cost basis for any retained interests that are recorded upon the deconsolidation of a VIE. Any difference between the fair value and the previous carrying amount of our investment in the VIE is recorded as “Investment gains, net” in our consolidated statements of operations and comprehensive income. Purchase/Sale of Fannie Mae Securities We actively purchase and may subsequently sell guaranteed MBS that have been issued through lender swap and portfolio securitization transactions. The accounting for the purchase and sale of our guaranteed MBS issued by the trusts differs based on the characteristics of the securitization trusts and whether the trusts are consolidated. Single-Class Securitization Trusts We create single-class securitization trusts to issue single-class Fannie Mae MBS that evidence an undivided interest in the mortgage loans held in the trust. Investors in single-class Fannie Mae MBS receive principal and interest payments in proportion to their percentage ownership of the MBS issuance. We guarantee to each single-class securitization trust that we will supplement amounts received by the single-class securitization trust as required to permit timely payments of principal and interest on the related Fannie Mae MBS. This guaranty exposes us to credit losses on the loans underlying Fannie Mae MBS. Single-class securitization trusts are used for lender swap and portfolio securitization transactions. A lender swap transaction occurs when a mortgage lender delivers a pool of single-family mortgage loans to us, which we immediately deposit into an MBS trust. The MBS are then issued to the lender in exchange for the mortgage loans. A portfolio securitization transaction occurs when we purchase mortgage loans from third-party sellers for cash and later deposit these loans into an MBS trust. The securities issued through a portfolio securitization are then sold to investors for cash. We consolidate single-class securitization trusts that are issued under these programs when our role as guarantor and master servicer provides us with the power to direct matters, such as the servicing of the mortgage loans, that impact the credit risk to which we are exposed. In contrast, we do not consolidate single-class securitization trusts when other organizations have the power to direct these activities ( e.g ., when the loan collateral is subject to a Federal Housing Administration guaranty and related Servicing Guide). When we purchase single-class Fannie Mae MBS issued from a consolidated trust, we account for the transaction as an extinguishment of the related debt in our consolidated financial statements. We record a gain or loss on the extinguishment of such debt to the extent that the purchase price of the MBS does not equal the carrying value of the related consolidated debt reported in our consolidated balance sheets (including unamortized premiums, discounts or the other cost basis adjustments) at the time of purchase. When we sell single-class Fannie Mae MBS that were issued from a consolidated trust, we account for the transaction as the issuance of debt in our consolidated financial statements. We amortize the related premiums, discounts and other cost basis adjustments into income over time. If a single-class securitization trust is not consolidated, we account for the purchase and subsequent sale of such securities as the transfer of an investment security in accordance with the accounting guidance for transfers of financial assets. Single-Class Resecuritization Trusts Single-class resecuritization trusts (Fannie Megas ® ) are created by depositing Fannie Mae MBS into a new securitization trust for the purpose of aggregating multiple MBS into a single larger security. The cash flows from the new security represent an aggregation of the cash flows from the underlying MBS. We guarantee to each single-class resecuritization trust that we will supplement amounts received by the trust as required to permit timely payments of principal and interest on the related Fannie Mae securities. However, we assume no additional credit risk in such a resecuritization transaction, because the underlying assets are MBS for which we have already provided a guaranty. Additionally, our involvement with these trusts does not provide any incremental rights or power that would enable Fannie Mae to direct any activities of the trusts. As a result, we have concluded that we are not the primary beneficiaries of, and therefore do not consolidate, our single-class resecuritization trusts. As our single-class resecuritization securities pass through all of the cash flows of the underlying MBS directly to the holders of the securities, they are deemed to be substantially the same as the underlying MBS. Therefore, we account for purchases of our single-class resecuritization securities as an extinguishment of the underlying MBS debt and the sale of these securities as an issuance of the underlying MBS debt. Multi-Class Resecuritization Trusts Multi-class resecuritization trusts are trusts we create to issue multi-class Fannie Mae securities, including Real Estate Mortgage Investment Conduit (“REMIC”) and interest-only and principal-only strip securities, in which the cash flows of the underlying mortgage assets are divided, creating several classes of securities, each of which represents a beneficial ownership interest in a separate portion of cash flows. We guarantee to each multi-class resecuritization trust that we will supplement amounts received by the trusts as required to permit timely payments of principal and interest, as applicable, on the related Fannie Mae securities. However, we assume no additional credit risk in such a resecuritization transaction because the underlying assets are Fannie Mae MBS for which we have already provided a guaranty. Although we may be exposed to prepayment risk via our ownership of the securities issued by these trusts, we do not have the ability via our involvement with a multi-class resecuritization trust to impact the economic risk to which we are exposed. Therefore, we do not consolidate such a multi-class resecuritization trust until we hold a substantial portion of the outstanding beneficial interests that have been issued by the trust and are therefore considered the primary beneficiary of the trust. In contrast to our single-class resecuritization trust, the cash flows from the underlying MBS are divided between the debt securities issued by the multi-class resecuritization trust, and therefore, the debt issued by a multi-class resecuritization trust is not substantially the same as the consolidated MBS debt. As a result, if a multi-class resecuritization trust is not consolidated, we account for the purchase and sale of such securities as the transfer of an investment security in accordance with the accounting guidance for the transfers of financial assets rather than the issuance or extinguishment of the related multi-class debt. However, if a multi-class resecuritization trust is consolidated, we account for the purchase of the securities issued by consolidated multi-class resecuritization trusts as an extinguishment of the debt issued by these trusts and the subsequent sale of such securities as the issuance of multi-class debt. When we do not consolidate a multi-class resecuritization trust, we recognize in our consolidated financial statements both our investment in the trust and the mortgage loans of the Fannie Mae MBS trusts that we consolidate that underlie the multi-class resecuritization trust. Additionally, we recognize the unsecured corporate debt issued to third parties to fund the purchase of our investments in the multi-class resecuritization trusts and the debt issued to third parties of the MBS trusts we consolidate that underlie the multi-class resecuritization trusts. This results in the recognition of interest income from investments in multi-class resecuritization trusts and interest expense from the unsecured debt issued to third parties to fund the purchase of the investments in multi-class resecuritization trusts, as well as interest income from the mortgage loans and interest expense from the debt issued to third parties from the MBS trusts we consolidate that underlie the multi-class resecuritization trusts.
Transfers and Servicing of Financial Assets, Policy [Policy Text Block]	Transfers of Financial Assets We evaluate a transfer of financial assets to determine whether the transfer qualifies as a sale. If the transfer does not meet the criteria for sale treatment, the transferred assets remain in our consolidated balance sheets and we record a liability to the extent of any proceeds received in connection with such a transfer. Transfers of financial assets for which we surrender control of the transferred assets are recorded as sales. When a transfer that qualifies as a sale is completed, we derecognize all assets transferred and recognize all assets obtained and liabilities incurred at fair value. The difference between the carrying basis of the assets transferred and the fair value of the proceeds from the sale is recorded as a component of “Investment gains, net” in our consolidated statements of operations and comprehensive income. Retained interests are primarily derived from transfers associated with our portfolio securitizations in the form of Fannie Mae MBS, REMIC certificates, guaranty assets and master servicing assets. We separately describe the subsequent accounting, as well as how we determine fair value, for our retained interests in the Fannie Mae MBS included in the “Investments in Securities” section of this note. We enter into repurchase agreements that involve contemporaneous trades to purchase and sell securities. These transactions are accounted for as secured financings since the transferor has not relinquished control over the transferred assets. These transactions are reported as securities purchased under agreements to resell and securities sold under agreements to repurchase in our consolidated balance sheets except for securities purchased under agreements to resell on an overnight basis, which are included in cash and cash equivalents in our consolidated balance sheets. Transfers of Financial Assets We issue Fannie Mae MBS through portfolio securitization transactions by transferring pools of mortgage loans or mortgage-related securities to one or more trusts or special purpose entities. We are considered to be the transferor when we transfer assets from our own retained mortgage portfolio in a portfolio securitization transaction.
Cash and Cash Equivalents, Policy [Policy Text Block]	Cash and Cash Equivalents and Statements of Cash Flows Short-term investments that have a maturity at the date of acquisition of three months or less and are readily convertible to known amounts of cash are generally considered cash equivalents. We also include securities purchased under agreements to resell on an overnight basis in cash and cash equivalents in our consolidated balance sheets. We may pledge as collateral certain short-term investments classified as cash equivalents. In the presentation of our consolidated statements of cash flows, we present cash flows from derivatives that do not contain financing elements and mortgage loans held for sale at acquisition as operating activities. We present cash flows from federal funds sold and securities purchased under agreements to resell or similar arrangements as investing activities and cash flows from federal funds purchased and securities sold under agreements to repurchase as financing activities. We classify cash flows from trading securities based on their nature and purpose. We classify all cash flows from trading securities (U.S. Treasury securities and mortgage-related securities purchased subsequent to December 31, 2013) as operating activities as we do not intend to hold the securities for investment. We classify cash flows from mortgage-related trading securities purchased prior to January 1, 2014 that we intend to hold for investment as investing activities. For consolidated trusts, we classify cash flows related to mortgage loans held by our consolidated trusts as either investing activities (for principal repayments) or operating activities (for interest received from borrowers included as a component of our net income). Cash flows related to debt securities issued by consolidated trusts are classified as either financing activities (for repayments of principal to certificateholders) or operating activities (for interest payments to certificateholders included as a component of our net income). We distinguish between the payments and proceeds related to the debt of Fannie Mae and the debt of consolidated trusts, as applicable. We present our non-cash activities in the consolidated statements of cash flows at the associated unpaid principal balance.
Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block]	Restricted Cash We and our servicers advance payments on delinquent loans to consolidated Fannie Mae MBS trusts. We recognize the cash advanced as “Restricted cash” in our consolidated balance sheets to the extent such amounts are due to, but have not yet been remitted to, the MBS certificateholders. In addition, when we or our servicers collect and hold cash that is due to certain Fannie Mae MBS trusts in advance of our requirement to remit these amounts to the trusts, we recognize the collected cash amounts as “Restricted cash.” We also recognize “Restricted cash” as a result of restrictions related to certain consolidated partnership funds as well as for certain collateral arrangements for which we do not have the right to use the cash.
Marketable Securities, Policy [Policy Text Block]	Investments in Securities Securities Classified as Available-for-Sale or Trading We classify and account for our securities as either available-for-sale (“AFS”) or trading. We measure AFS securities at fair value in our consolidated balance sheets, with unrealized gains and losses included in “Accumulated other comprehensive income” (“AOCI”), net of income taxes. We recognize realized gains and losses on AFS securities when securities are sold. We calculate the gains and losses using the specific identification method and record them in “Investment gains, net” in our consolidated statements of operations and comprehensive income. We measure trading securities at fair value in our consolidated balance sheets with unrealized and realized gains and losses included as a component of “Fair value losses, net” in our consolidated statements of operations and comprehensive income. We include interest and dividends on securities in our consolidated statements of operations and comprehensive income. Interest income includes the amortization of cost basis adjustments, including premiums and discounts, recognized as a yield adjustment using the interest method over the contractual term of the security. As of December 31, 2017 , we did not have any securities classified as held-to-maturity. Fannie Mae MBS included in “Investments in securities” When we own Fannie Mae MBS issued by unconsolidated trusts, we do not derecognize any components of the guaranty assets, guaranty obligations, or any other outstanding recorded amounts associated with the guaranty transaction because our contractual obligation to the MBS trust remains in force until the trust is liquidated. We determine the fair value of Fannie Mae MBS based on observable market prices because most Fannie Mae MBS are actively traded. Fannie Mae MBS receive high credit quality ratings primarily because of our guaranty. The fair value of the guaranty obligation, net of deferred profit, associated with Fannie Mae MBS included in “Investments in securities” approximates the fair value of the credit risk that exists on these Fannie Mae MBS absent our guaranty. We record the aggregate amount of Fannie Mae MBS held as “Investments in securities” in our consolidated balance sheets. The unamortized obligation to stand ready to perform over the term of our guaranty and any incurred credit losses that relate to Fannie Mae MBS held as “Investments in securities” is included in “Other liabilities.” Upon subsequent sale of a Fannie Mae MBS, we continue to account for any outstanding recorded amounts associated with the guaranty transaction on the same basis of accounting as prior to the sale of Fannie Mae M
Available-for-sale Securities, Policy [Policy Text Block]	Other-Than-Temporary Impairment of Debt Securities We evaluate AFS securities for other-than-temporary impairment (“OTTI”) on a quarterly basis. OTTI is considered to have occurred when the fair value of a debt security is below its amortized cost basis and we intend to sell or it is more likely than not that we will be required to sell the security before recovery. In such cases, we recognize in “Investment gains, net” in our consolidated statements of operations and comprehensive income the entire difference between the amortized cost basis of the security and its fair value. OTTI is also considered to have occurred if we do not expect to recover the entire amortized cost basis of a debt security even if we do not intend to sell the security or it is not more likely than not we will be required to sell the security before recovery. We separate the difference between the amortized cost basis of the security and its fair value into the amount representing the credit loss, which we recognize in “Investment gains, net” in our consolidated statements of operations and comprehensive income, and the amount related to all other factors, which we recognize in “Total other comprehensive loss,” net of taxes, in our consolidated statements of operations and comprehensive income. We consider guarantees, insurance contracts or other credit enhancements (such as collateral) in determining our best estimate of cash flows expected to be collected only if (1) such guarantees, insurance contracts or other credit enhancements provide for payments to be made solely to reimburse us for failure of the issuer to satisfy its required payment obligations; (2) such guarantees, insurance contracts or other credit enhancements are contractually attached to the security; and (3) collection of the amounts receivable under these agreements is deemed probable. Guarantees, insurance contracts or other credit enhancements are considered contractually attached if they are part of and trade with the security upon transfer of the security to a third party. In periods after we recognize OTTI of debt securities, we use the prospective interest method to recognize interest income. Under the prospective interest method, we calculate a new effective yield for subsequent recognition of interest income and measurement of impairment when we determine that there has been a significant increase in expected or actual cash flows. We consider a significant increase in cash flows to be at least a 10% increase over two consecutive quarters of the expected or actual cash flows. We calculate the new effective yield by using the new cost basis and the significantly increased actual or expected cash flows. Available-for-Sale Securities We record AFS securities at fair value with unrealized gains and losses, recorded net of tax, as a component of “ Other comprehensive loss ” and we recognize realized gains and losses from the sale of AFS securities in “ Investment gains, net ” in our consolidated statements of operations and comprehensive income . Other-Than-Temporary Impairments For AFS securities, OTTI is considered to have occurred when the fair value of a debt security is below its amortized cost basis and we intend to sell or it is more likely than not that we will be required to sell the security before recovery. Additionally, OTTI is considered to have occurred if we do not expect to recover the entire amortized cost basis of a debt security even if we do not intend to sell the security or it is not more likely than not we will be required to sell the security before recovery.
Finance, Loan and Lease Receivables, Held-for-sale, Policy [Policy Text Block]	Loans Held for Sale When we acquire mortgage loans that we intend to sell or securitize via trusts that will not be consolidated, we classify the loans as held for sale (“HFS”). We report the carrying value of HFS loans at the lower of cost or fair value. Any excess of an HFS loan’s cost over its fair value is recognized as a valuation allowance, with changes in the valuation allowance recognized as “Investment gains, net” in our consolidated statements of operations and comprehensive income. We recognize interest income on HFS loans on an accrual basis, unless we determine that the ultimate collection of contractual principal or interest payments in full is not reasonably assured. Purchased premiums, discounts and other cost basis adjustments on HFS loans are deferred upon loan acquisition, included in the cost basis of the loan, and not amortized. We determine any lower of cost or fair value adjustment on HFS loans at an individual loan level. In the event that we reclassify held for investment (“HFI”) loans to HFS loans, based upon a change in our intent, we record the loans at lower of cost or fair value on the date of redesignation. If the amounts charged off upon redesignation exceed the allowance related to the loans, we record a provision for credit losses. If the amounts charged off are less than the allowance related to the loans, we recognize a benefit for credit losses. We recognize recoveries of previously charged-off amounts as a reduction to charge-offs. We report the carrying value of HFS loans at the lower of cost or fair value and record valuation changes in “Investment gains, net” in our consolidated statements of operations and comprehensive income.
Finance, Loan and Lease Receivables, Held-for-investment, Policy [Policy Text Block]	Loans Held for Investment When we acquire mortgage loans that we have the ability and the intent to hold for the foreseeable future or until maturity, we classify the loans as HFI. When we consolidate a trust, we recognize the loans underlying the trust in our consolidated balance sheets. The trusts do not have the ability to sell mortgage loans and the use of such loans is limited exclusively to the settlement of obligations of the trusts. Therefore, mortgages acquired when we have the intent to securitize via trusts that are consolidated will generally be classified as HFI in our consolidated balance sheets both prior to and subsequent to their securitization. We report the carrying value of HFI loans at the unpaid principal balance, net of unamortized premiums and discounts, other cost basis adjustments, and allowance for loan losses. We recognize interest income on HFI loans on an accrual basis using the interest method over the contractual life of the loan, including the amortization of any deferred cost basis adjustments, such as the premium or discount at acquisition, unless we determine that the ultimate collection of contractual principal or interest payments in full is not reasonably assured. We report the carrying value of HFI loans at the unpaid principal balance, net of unamortized premiums and discounts, other cost basis adjustments, and an allowance for loan losses. We define the recorded investment of HFI loans as unpaid principal balance, net of unamortized premiums and discounts, other cost basis adjustments, and accrued interest receivable.
Nonaccrual Loans [Policy Text Block]	Nonaccrual Loans We discontinue accruing interest on loans when we believe collectibility of principal or interest is not reasonably assured, which for a single-family loan we have determined, based on our historical experience, to be when the loan becomes two months or more past due according to its contractual terms. Interest previously accrued but not collected is reversed through interest income at the date a loan is placed on nonaccrual status. We return a non-modified single-family loan to accrual status at the point that the borrower brings the loan current. We return a modified single-family loan to accrual status at the point that the borrower successfully makes all required payments during the trial period (generally three to four months) and the modification is made permanent. We place a multifamily loan on nonaccrual status when the loan becomes three months or more past due according to its contractual terms or is deemed to be individually impaired, unless the loan is well secured such that collectibility of principal and accrued interest is reasonably assured. We return a multifamily loan to accrual status when the borrower cures the delinquency of the loan or we otherwise determine that the loan is well secured such that collectibility is reasonably assured.
Troubled Debt Restructurings [Policy Text Block]	Restructured Loans A modification to the contractual terms of a loan that results in granting a concession to a borrower experiencing financial difficulties is considered a troubled debt restructuring (“TDR”). Our loss mitigation programs primarily include modifications that result in the capitalization of past due amounts in combination with interest rate reductions and/or the extension of the loan’s maturity date. Such restructurings are granted to borrowers in financial difficulty on either a permanent or contingent basis, as in the case of modifications with a trial period. We consider these types of loan restructurings to be TDRs. We generally do not include principal or past due interest forgiveness as part of our loss mitigation programs, and, as a result, we generally do not charge off any outstanding principal or accrued interest amounts at the time of loan modification. We believe that the loan underwriting activities we perform as a part of our loan modification process coupled with the borrower’s successful performance during any required trial period provide us reasonable assurance regarding the collectibility of the principal and interest due in accordance with the loan’s modified terms, which include any past due interest amounts that are capitalized as principal at the time of modification. As such, the loan is returned to accrual status when the loan modification is completed ( i.e ., at the end of the trial period), and we accrue interest thereafter in accordance with our interest accrual policy. If the loan was on nonaccrual status prior to entering the trial period, it remains on nonaccrual status until the borrower demonstrates performance via the trial period and the modification is finalized. In addition to these loan modifications, we also engage in other loss mitigation activities with troubled borrowers, which include repayment plans, forbearance arrangements, and the capitalization only of past due amounts. Repayment plans and forbearance arrangements are informal agreements with the borrower that do not result in the legal modification of the loan. For all of these activities, we consider the deferral or capitalization of three or fewer missed payments to represent only an insignificant delay, and thus not a TDR. If we defer or capitalize more than three missed payments, the delay is no longer considered insignificant, and the restructuring is accounted for as a TDR. We measure impairment of a loan restructured in a TDR individually based on the excess of the recorded investment in the loan over the present value of the expected future cash inflows discounted at the loan’s original effective interest rate. Costs incurred to complete a TDR are expensed as incurred. However, when foreclosure is probable on an individually impaired loan, we measure impairment based on the difference between our recorded investment in the loan and the fair value of the underlying property, adjusted for the estimated costs to sell the property and estimated insurance or other proceeds we expect to receive. A modification to the contractual terms of a loan that results in granting a concession to a borrower experiencing financial difficulties is considered a TDR. In addition to formal loan modifications, we also engage in other loss mitigation activities with troubled borrowers, which include repayment plans and forbearance arrangements, both of which represent informal agreements with the borrower that do not result in the legal modification of the loan’s contractual terms. We account for these informal restructurings as a TDR if we defer more than three missed payments. We also classify loans to certain borrowers who have received bankruptcy relief as TDRs.
Allowance for Loan Losses [Policy Text Block]	Allowance for Loan Losses and Reserve for Guaranty Losses Our allowance for loan losses is a valuation allowance that reflects an estimate of incurred credit losses related to our recorded investment in both single-family and multifamily HFI loans. This population includes both HFI loans held by Fannie Mae and by consolidated Fannie Mae MBS trusts. When calculating our allowance for loan losses, we consider only our net recorded investment in the loan at the balance sheet date, which includes the loan’s unpaid principal balance and any applicable cost basis adjustments. We record charge-offs as a reduction to the allowance for loan losses when losses are confirmed through the receipt of assets in satisfaction of a loan, such as the underlying collateral upon foreclosure or cash upon completion of a short sale. Additionally, we record charge-offs as a reduction to our allowance for loan losses when a loan is determined to be uncollectible, upon the redesignation of loans from HFI to HFS and pursuant to the charge-off provisions of the Advisory Bulletin. The reserve for guaranty losses is a liability account which is a component of “Other liabilities” in our consolidated balance sheets that reflects an estimate of incurred credit losses related to our guaranty to each unconsolidated Fannie Mae MBS trust that we will supplement amounts received by the Fannie Mae MBS trust as required to permit timely payments of principal and interest on the related Fannie Mae MBS and our agreements to purchase credit-impaired loans from lenders under the terms of our long-term standby commitments. As a result, the reserve for guaranty losses considers not only the principal and interest due on the loan at the current balance sheet date, but also any additional interest payments due to the trust from the current balance sheet date until the point of loan acquisition or foreclosure. We maintain an allowance for loan losses for HFI loans held by Fannie Mae and loans backing Fannie Mae MBS issued from consolidated trusts. When calculating our allowance for loan losses, we consider the unpaid principal balance, net of amortized premiums and discounts, and other cost basis adjustments of HFI loans at the balance sheet date.
Impaired Financing Receivable, Policy [Policy Text Block]	Single-Family Loans We recognize credit losses related to groups of similar single-family HFI loans that are not individually impaired when (1) available information as of each balance sheet date indicates that it is probable a loss has occurred and (2) the amount of the loss can be reasonably estimated. We aggregate such loans, based on similar risk characteristics, for purposes of estimating incurred credit losses and establish a collective single-family loss reserve using an econometric model that derives an overall loss reserve estimate. The estimate takes into account multiple factors which include but are not limited to origination year, loan product type, mark-to-market LTV ratio, and delinquency status. Once loans are aggregated, there typically is not a single, distinct event that would result in an individual loan or pool of loans being impaired. In determining our collective reserve, we base our allowance methodology on historical events and trends, such as loss severity (in event of default), default rates, and recoveries from mortgage insurance contracts and other credit enhancements that provide loan level loss coverage and are either contractually attached to a loan or that were entered into contemporaneously with and in contemplation of a guaranty or loan purchase transaction. We use recent regional historical sales and appraisal information, including the sales of our own foreclosed properties, to develop our loss severity estimates for all loan categories. Our allowance calculation also incorporates a loss confirmation period (the anticipated time lag between a credit loss event and the confirmation of the credit loss resulting from that event) to ensure our allowance estimate captures credit losses that have been incurred as of the balance sheet date but have not been confirmed. In addition, management performs a review of the observable data used in its estimate to ensure it is representative of prevailing economic conditions and other events existing as of the balance sheet date. We record charge-offs as a reduction to the allowance for loan losses when losses are confirmed through the receipt of assets in full satisfaction of a loan, such as the underlying collateral upon foreclosure or cash upon completion of a short sale. Additionally, we record charge-offs as a reduction to our allowance for loan losses when a loan is determined to be uncollectible, upon the redesignation of loans from HFI to HFS and pursuant to the charge-off provisions of the Advisory Bulletin. The excess of a loan’s unpaid principal balance, accrued interest, and any applicable cost basis adjustments (“our total exposure”) over the fair value of the assets is treated as a charge-off loss that is deducted from the allowance for loan losses. The amount charged off also considers estimated proceeds from primary mortgage insurance or other credit enhancements that are either contractually attached to a loan or that were entered into contemporaneously with and in contemplation of a guaranty or loan purchase transaction as a recovery of our total exposure, up to the amount of loss recognized as a charge-off. We record additional proceeds from primary mortgage insurance and credit enhancements in excess of our total exposure as a recovery of any forgone contractually past due interest, and then as an offset to the expenses recorded in “Foreclosed property expense” in our consolidated statements of operations and comprehensive income when received. Individually Impaired Single-Family Loans Individually impaired single-family loans currently include those we restructure in troubled debt restructurings. We consider a loan to be impaired when, based on current information, it is probable that we will not receive all amounts due, including interest, in accordance with the contractual terms of the loan agreement. When making our assessment as to whether a loan is impaired, we also take into account more than insignificant delays in payment and shortfalls in amounts received. Determination of whether a delay in payment or shortfall in amount is more than insignificant requires management’s judgment as to the facts and circumstances surrounding the loan. Our measurement of impairment on an individually impaired loan follows the method that is most consistent with our expectations of recovery of our recorded investment in the loan. When a loan has been restructured, we measure impairment using a cash flow analysis discounted at the loan’s original effective interest rate. If we expect to recover our recorded investment in an individually impaired loan through probable foreclosure of the underlying collateral, we measure impairment based on the difference between our recorded investment in the loan and the fair value of the underlying property, adjusted for the estimated costs to sell the property and estimated insurance or other proceeds we expect to receive. For individually impaired loans that we believe are probable of foreclosure, we take into consideration the sales prices of foreclosed properties in determining the value of the underlying real estate collateral. We use internal models to project cash flows used to assess impairment of individually impaired loans, and generally update the market and loan characteristic inputs we use in these models monthly, using month-end data. Market inputs include information such as interest rates, volatility and spreads, while loan characteristic inputs include information such as mark-to-market LTV ratios and delinquency status. The loan characteristic inputs are key factors that affect the predicted rate of default for loans evaluated for impairment through our internal cash flow models. For example, loans with an unsuccessful trial modification, which are often accompanied by high delinquency rates, have much higher predicted default rates compared to performing loans with completed modifications, particularly those with a significant payment reduction in the borrower’s required monthly payment. We evaluate the reasonableness of our models by comparing the results with actual performance and our assessment of current market conditions. In addition, we review our models at least annually for reasonableness and predictive ability in accordance with our corporate model review policy. Accordingly, we believe the projected cash flows generated by our models that we use to assess impairment appropriately reflect the expected future performance of the loans. Multifamily Loans We identify multifamily loans for evaluation for impairment through a credit risk assessment process. If we determine that a multifamily loan is individually impaired, we generally measure impairment on that loan based on the fair value of the underlying collateral less estimated costs to sell the property. For groups of smaller-balance homogeneous multifamily loans, we evaluate collectively for impairment. We establish a collective multifamily loss reserve for all loans in our multifamily guaranty book of business, that are not individually impaired, using an internal model that applies loss factors to loans in similar risk categories. We categorize loan credit risk based on relevant observable data about a borrower’s ability to pay, including multifamily market fundamentals such as vacancy rates and rents, review of available current borrower financial information, operating statements on the underlying collateral, current debt service coverage ratios (“DSCRs”), historical payment experience, estimates of the current collateral values and other related credit documentation. For each risk category, certain observed default probability and loss severity (in event of default) factors, based on historical performance of loans in the same risk category, are applied against our recorded investment in the loans to determine an appropriate allowance. Such performance data reflect historical delinquencies and charge-offs, as well as loan size. In addition, we consider any credit enhancements such as letters of credit or loss sharing arrangements with our lenders.
Advances to Lenders [Policy Text Block]	Advances to Lenders Advances to lenders represent our payments of cash in exchange for the receipt of mortgage loans from lenders in a transfer that is accounted for as a secured lending arrangement. These transfers primarily occur when we provide early funding to lenders for loans that they will subsequently either sell to us or securitize into a Fannie Mae MBS that they will deliver to us. We individually negotiate early lender funding advances with our lender customers. Early lender funding advances have terms up to 60 days and earn a short-term market rate of interest. We report cash outflows from advances to lenders as an investing activity in our consolidated statements of cash flows. Settlements of the advances to lenders, other than through lender repurchases of loans, are not collected in cash, but rather in the receipt of either loans or Fannie Mae MBS. Accordingly, this activity is reflected as a non-cash transfer in our consolidated statements of cash flows in the line item entitled “Transfers from advances to lenders to loans held for investment of consolidated trusts.”
Finance, Loan and Lease Receivables, Held for Investments, Foreclosed Assets Policy [Policy Text Block]	Acquired Property, Net We recognize foreclosed property ( i.e. , “Acquired property, net”) upon the earlier of the loan foreclosure event or when we take physical possession of the property ( i.e. , through a deed-in-lieu of foreclosure transaction). We initially measure foreclosed property at its fair value less its estimated costs to sell. We treat any excess of our recorded investment in the loan over the fair value less estimated costs to sell the property as a charge-off to the “Allowance for loan losses” in our consolidated balance sheets. Any excess of the fair value less estimated costs to sell the property over our recorded investment in the loan is recognized first to recover any forgone, contractually due interest, then to “Foreclosed property expense” in our consolidated statements of operations and comprehensive income. We classify foreclosed properties as HFS when we intend to sell the property and the following conditions are met at either acquisition or within a relatively short period thereafter: we are actively marketing the property and it is available for immediate sale in its current condition such that the sale is reasonably expected to take place within one year. We report these properties at the lower of their carrying amount or fair value less estimated selling costs. We do not depreciate these properties. We recognize a loss for any subsequent write-down of the property to its fair value less its estimated costs to sell through a valuation allowance with an offsetting charge to “Foreclosed property expense” in our consolidated statements of operations and comprehensive income. We recognize a recovery for any subsequent increase in fair value less estimated costs to sell up to the cumulative loss previously recognized through the valuation allowance. We recognize gains or losses on sales of foreclosed property through “Foreclosed property expense” in our consolidated statements of operations and comprehensive income. Properties that do not meet the criteria to be classified as HFS are classified as held for use and are recorded in “Other assets” in our consolidated balance sheets. These properties are depreciated and are evaluated for impairment when circumstances indicate that the carrying amount of the property is no longer recoverable.
Commitments to Purchase and Sell Mortgage Loans and Securities [Policy Text Block]	Commitments to Purchase and Sell Mortgage Loans and Securities We enter into commitments to purchase and sell mortgage-backed securities and to purchase single-family and multifamily mortgage loans. Certain commitments to purchase or sell mortgage-backed securities and to purchase single-family mortgage loans are generally accounted for as derivatives. Our commitments to purchase multifamily loans are not accounted for as derivatives because they do not meet the criteria for net settlement. When derivative purchase commitments settle, we include the fair value on the settlement date in the cost basis of the loan or unconsolidated security we purchase. When derivative commitments to sell securities settle, we include the fair value of the commitment on the settlement date in the cost basis of the security we sell. Purchases and sales of securities issued by our consolidated MBS trusts are treated as extinguishment or issuance of debt, respectively. For commitments to purchase and sell securities issued by our consolidated MBS trusts, we recognize the fair value of the commitment on the settlement date as a component of debt extinguishment gains and losses or in the cost basis of the debt issued, respectively. Regular-way securities trades provide for delivery of securities within the time generally established by regulations or conventions in the market in which the trade occurs and are exempt from application of derivative accounting. Commitments to purchase or sell securities that we account for on a trade-date basis are also exempt from the derivative accounting requirements. We record the purchase and sale of an existing security on its trade date when the commitment to purchase or sell the existing security settles within the period of time that is customary in the market in which those trades take place. Additionally, contracts for the forward purchase or sale of when-issued and to-be-announced (“TBA”) securities are exempt from the derivative accounting requirements if there is no other way to purchase or sell that security, delivery of that security and settlement will occur within the shortest period possible for that type of security, and it is probable at inception and throughout the term of the individual contract that physical delivery of the security will occur. Since our commitments for the purchase of when-issued and TBA securities can be net settled and we do not document that physical settlement is probable, we account for all such commitments as derivatives.
Derivatives, Policy [Policy Text Block]	Derivative Instruments We recognize all derivatives as either assets or liabilities in our consolidated balance sheets at their fair value on a trade date basis. We report derivatives in a gain position after offsetting by counterparty in “Other assets” and derivatives in a loss position after offsetting by counterparty in “Other liabilities” in our consolidated balance sheets. • Interest rate swap contracts. An interest rate swap is a transaction between two parties in which each party agrees to exchange payments tied to different interest rates or indices for a specified period of time, generally based on a notional amount of principal. The types of interest rate swaps we use include pay-fixed swaps, receive-fixed swaps and basis swaps. • Interest rate option contracts. These contracts primarily include pay-fixed swaptions, receive-fixed swaptions, cancelable swaps and interest rate caps. A swaption is an option contract that allows us or a counterparty to enter into a pay-fixed or receive-fixed swap at some point in the future. • Foreign currency swaps. These swaps convert debt that we issue in foreign denominated currencies into U.S. dollars. We enter into foreign currency swaps only to the extent that we hold foreign currency debt. • Futures. These are standardized exchange-traded contracts that either obligate a buyer to buy an asset at a predetermined date and price or a seller to sell an asset at a predetermined date and price. The types of futures contracts we enter into include Eurodollar, U.S. Treasury and swaps.
Derivatives, Offsetting Fair Value Amounts, Policy [Policy Text Block]	We offset the carrying amounts of certain derivatives that are in gain positions and loss positions with the same counterparty as well as cash collateral receivables and payables associated with derivative positions under master netting arrangements. We offset these amounts only when we have the legal right to offset under the contract and we have met all of the offsetting conditions. We determine our rights to offset the assets and liabilities presented above with the same counterparty, including collateral posted or received, based on the contractual arrangements entered into with our individual counterparties and various rules and regulations that would govern the insolvency of a derivative counterparty. Derivative instruments are recorded at fair value and securities purchased under agreements to resell or similar arrangements are recorded at amortized cost in our consolidated balance sheets.
Derivatives, Embedded Derivatives [Policy Text Block]	We evaluate financial instruments that we purchase or issue and other financial and non-financial contracts for embedded derivatives. To identify embedded derivatives that we must account for separately, we determine if: (1) the economic characteristics of the embedded derivative are not clearly and closely related to the economic characteristics of the financial instrument or other contract ( i.e ., the host contract); (2) the financial instrument or other contract itself is not already measured at fair value with changes in fair value included in earnings; and (3) a separate instrument with the same terms as the embedded derivative would meet the definition of a derivative. If the embedded derivative meets all three of these conditions we elect to carry the hybrid contract in its entirety at fair value with changes in fair value recorded in earnings.
Repurchase Agreements, Collateral, Policy [Policy Text Block]	Collateral We enter into various transactions where we pledge and accept collateral, the most common of which are our derivative transactions. Required collateral levels vary depending on the credit rating and type of counterparty. We also pledge and receive collateral under our repurchase and reverse repurchase agreements. In order to reduce potential exposure to repurchase counterparties, a third-party custodian typically maintains the collateral and any margin. We monitor the fair value of the collateral received from our counterparties, and we may require additional collateral from those counterparties, as we deem appropriate. Cash Collateral We record cash collateral accepted from a counterparty that we have the right to use as “Cash and cash equivalents” and cash collateral accepted from a counterparty that we do not have the right to use as “Restricted cash” in our consolidated balance sheets. We net our obligation to return cash collateral pledged to us against the fair value of derivatives in a gain position recorded in “Other assets” in our consolidated balance sheets as part of our counterparty netting calculation. For derivative positions with the same counterparty under master netting arrangements where we pledge cash collateral, we remove it from “Cash and cash equivalents” and net the right to receive it against the fair value of derivatives in a loss position recorded in “Other liabilities” in our consolidated balance sheets as a part of our counterparty netting calculation. Non-Cash Collateral We classify securities pledged to counterparties as either “Investments in securities” or “Cash and cash equivalents” in our consolidated balance sheets. Securities pledged to counterparties that have been consolidated with the underlying assets recognized as loans are included as “Mortgage loans” in our consolidated balance sheets. Our liability to third party holders of Fannie Mae MBS that arises as the result of a consolidation of a securitization trust is collateralized by the underlying loans and/or mortgage-related securities.
Debt, Policy [Policy Text Block]	Debt Our consolidated balance sheets contain debt of Fannie Mae as well as debt of consolidated trusts. We report debt issued by us as “Debt of Fannie Mae” and by consolidated trusts as “Debt of consolidated trusts.” Debt issued by us represents debt that we issue to third parties to fund our general business activities and our credit risk-sharing securities. The debt of consolidated trusts represents the amount of Fannie Mae MBS issued from such trusts which is held by third-party certificateholders and prepayable without penalty at any time. We report deferred items, including premiums, discounts and other cost basis adjustments, as adjustments to the related debt balances in our consolidated balance sheets. When we purchase a Fannie Mae MBS issued from a consolidated single-class securitization trust, we extinguish the related debt of the consolidated trust as the MBS debt is no longer owed to a third-party. We record debt extinguishment gains or losses related to debt of consolidated trusts to the extent that the purchase price of the MBS does not equal the carrying value of the related consolidated MBS debt reported in our consolidated balance sheets (including unamortized premiums, discounts and other cost basis adjustments) at the time of purchase as a component of “Other expenses, net” in our consolidated statements of operations and comprehensive income.
Interest Expense, Policy [Policy Text Block]	We classify interest expense as either short-term or long-term based on the contractual maturity of the related debt. We recognize the amortization of premiums, discounts and other cost basis adjustments through interest expense using the effective interest method usually over the contractual term of the debt. Amortization of premiums, discounts and other cost basis adjustments begins at the time of debt issuance.
Income Tax, Policy [Policy Text Block]	Income Taxes We recognize deferred tax assets and liabilities based on the differences in the book and tax bases of assets and liabilities. We measure deferred tax assets and liabilities using enacted tax rates that are applicable to the period(s) that the differences are expected to reverse. We adjust deferred tax assets and liabilities for the effects of changes in tax laws and rates in the period of enactment. We recognize investment and other tax credits through our effective tax rate calculation assuming that we will be able to realize the full benefit of the credits. We reduce our deferred tax assets by an allowance if, based on the weight of available positive and negative evidence, it is more likely than not (a probability of greater than 50%) that we will not realize some portion, or all, of the deferred tax asset. We recognize deferred tax assets and liabilities for future tax consequences arising from differences between the carrying amounts of existing assets and liabilities under GAAP and their respective tax bases.
Income Tax Uncertainties, Policy [Policy Text Block]	We account for uncertain tax positions using a two-step approach whereby we recognize an income tax benefit if, based on the technical merits of a tax position, it is more likely than not that the tax position would be sustained upon examination by the taxing authority, which includes all related appeals and litigation. We then measure the recognized tax benefit based on the largest amount of tax benefit that is greater than 50% likely to be realized upon settlement with the taxing authority, considering all information available at the reporting date. We recognize interest expense and penalties on unrecognized tax benefits as “Other expenses, net” in our consolidated statements of operations and comprehensive income.
Earnings Per Share, Policy [Policy Text Block]	Earnings (Loss) per Share Earnings (loss) per share (“EPS”) is presented for basic and diluted EPS. We compute basic EPS by dividing net income (loss) attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period. Weighted average common shares includes 4.6 billion shares for the years ended December 31, 2017 , 2016 and 2015 that would be issued upon the full exercise of the warrant issued to Treasury from the date the warrant was issued through December 31, 2017 , 2016 and 2015 , respectively. The calculation of income available to common stockholders and EPS is based on the underlying premise that all income after payment of dividends on preferred shares is available to and will be distributed to the common stockholders. However, as a result of our conservatorship status and the terms of our agreements with Treasury, no amounts are available to distribute as dividends to common or preferred stockholders (other than to Treasury as holder of the senior preferred stock). Dividends distributed or available for distribution were calculated based on our net worth as of the end of the applicable fiscal quarters for each respective year, less the applicable capital reserve amount; however, the dividend payment for the fourth quarter of 2017 was reduced by $2.4 billion from the otherwise payable amount as a result of the December 2017 letter agreement with Treasury. The calculation of diluted EPS includes all the components of basic earnings per share, plus the dilutive effect of common stock equivalents such as convertible securities and stock options. Weighted average shares outstanding is increased to include the number of additional common shares that would have been outstanding if the dilutive potential common shares had been issued. Our diluted EPS weighted average shares outstanding includes 131 million shares of convertible preferred stock for the year ended December 31, 2016 . During periods in which a net loss attributable to common stockholders has been incurred, the years ended December 31, 2017 and 2015 , potential common equivalent shares outstanding are not included in the calculation because it would have an anti-dilutive effect.
Compensatory Fees, Policy [Policy Text Block]	Compensatory Fees We charge our primary servicers a compensatory fee for servicing delays within their control when they fail to comply with our established loss mitigation and foreclosure timelines. Compensatory fees are intended to compensate us for damages attributed to such servicing delays and to emphasize the importance of servicer performance. We recognize a compensatory fee receivable when the amounts are chargeable per our guidelines and are considered reasonably assured of collection. We subsequently establish a valuation allowance for any amounts we estimate to be uncollectible. If such fees are not reasonably assured of collection, we recognize them on a cash basis when received. The income associated with these fees is recognized as a component of “Foreclosed property expense” in our consolidated statements of operations and comprehensive income.
New Accounting Pronouncements, Policy [Policy Text Block]	New Accounting Guidance In May 2014, the Financial Accounting Standards Board (“FASB”) issued guidance on revenue from contracts with customers. The standard outlines a single model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance. The following contracts with customers are excluded from the scope of the new standard and will continue to be accounted for under existing guidance: leases, insurance, financial instruments ( e.g. , receivables, investments, liabilities, debt and derivatives) and guarantees. The new guidance became effective for us on January 1, 2018. We have evaluated this guidance and determined it will not have a material impact on our consolidated financial statements. In January 2016, the FASB issued guidance which makes limited amendments to the accounting related to the classification and measurement of financial instruments. The new guidance revises the accounting requirements related to (1) the classification and measurement of investments in equity securities and (2) the presentation of certain fair value changes for financial liabilities measured at fair value. It also amends certain disclosure requirements associated with the fair value of financial instruments. The new guidance became effective for us on January 1, 2018. We have evaluated this guidance and determined it will not have a material impact on our consolidated financial statements. In February 2016, the FASB issued guidance on leases. The guidance clarified the definition of a lease and requires lessees to recognize on the balance sheet a right-of-use asset, representing its right to use the underlying asset for the lease term, and a corresponding lease liability for all leases with terms greater than 12 months. This guidance supersedes the existing lease guidance; however, we must continue to classify leases to determine how to recognize lease-related expense in our consolidated statements of operations and comprehensive income. The new guidance is effective for us on January 1, 2019. We have evaluated this guidance and determined it will not have a material impact on our consolidated financial statements. In June 2016, the FASB issued guidance that changes the impairment model for most financial assets and certain other instruments. For loans, held-to-maturity debt securities and other financial assets recorded at amortized cost, entities will be required to use a new forward-looking “expected loss” model that will replace today’s “incurred loss” model and generally will result in the earlier recognition of allowance for loan losses. The guidance is effective on January 1, 2020 with early adoption permitted on January 1, 2019. We will adopt the standard on January 1, 2020. We will recognize the impact of the new guidance through a cumulative effect adjustment to retained earnings as of the beginning of the year of adoption. We are continuing to evaluate the impact of this guidance on our consolidated financial statements. We expect the greater impact of the guidance to relate to our accounting for credit losses for loans that are not individually impaired. The adoption of this guidance may decrease, perhaps substantially, our retained earnings and increase our allowance for loan losses. In August 2016, the FASB issued guidance regarding classification of certain items within the statement of cash flows in order to reduce diversity in practice with respect to cash flow classifications. The guidance became effective for us on January 1, 2018. We have evaluated this guidance and determined it will not have a material impact on our consolidated financial statements. In November 2016, the FASB issued guidance regarding the presentation of restricted cash in the statement of cash flows. The new guidance reduces diversity in how entities present changes in restricted cash and restricted cash equivalents with respect to the statements of cash flow. The guidance became effective for us on January 1, 2018. We have evaluated this guidance and determined it will not have a material impact on our consolidated financial statements. In August 2017, the FASB issued changes to the hedge accounting guidance that are intended to more closely align hedge accounting with companies’ risk management strategies, simplify the application of hedge accounting, and increase transparency as to the scope and results of hedging programs. The revised guidance will make more financial and nonfinancial hedging strategies eligible for hedge accounting. It also amends the presentation and disclosure requirements and changes how companies assess the effectiveness of hedging relationships. The guidance is effective January 1, 2019 and early adoption is permitted. Hedge accounting is elective and, while we do not currently have a hedge accounting program, we are actively considering electing a hedge accounting program in the future.

Consolidations and Transfers 27

Consolidations and Transfers of Financial Assets (Policies)	12 Months Ended
	Dec. 31, 2017
Consolidations and Transfers of Financial Assets [Abstract]
Consolidations, Policy [Policy Text Block]	Principles of Consolidation Our consolidated financial statements include our accounts as well as the accounts of the other entities in which we have a controlling financial interest. All intercompany balances and transactions have been eliminated. The typical condition for a controlling financial interest is ownership of a majority of the voting interests of an entity. A controlling financial interest may also exist in entities through arrangements that do not involve voting interests, such as a VIE. We have interests in various entities that are considered to be VIEs. The primary types of entities are securitization trusts guaranteed by us via lender swap and portfolio securitization transactions and mortgage-backed trusts that were not created by us, as well as housing partnerships that are established to finance the acquisition, construction, development or rehabilitation of affordable multifamily and single-family housing. These interests include investments in securities issued by VIEs, such as Fannie Mae MBS created pursuant to our securitization transactions and our guaranty to the entity. We consolidate the substantial majority of our single-class securitization trusts because our role as guarantor and master servicer provides us with the power to direct matters (primarily the servicing of mortgage loans) that impact the credit risk to which we are exposed. In contrast, we do not consolidate single-class securitization trusts when other organizations have the power to direct these activities. Unconsolidated VIEs We do not consolidate VIEs when we are not deemed to be the primary beneficiary.
Transfers and Servicing of Financial Assets, Policy [Policy Text Block]	Transfers of Financial Assets We evaluate a transfer of financial assets to determine whether the transfer qualifies as a sale. If the transfer does not meet the criteria for sale treatment, the transferred assets remain in our consolidated balance sheets and we record a liability to the extent of any proceeds received in connection with such a transfer. Transfers of financial assets for which we surrender control of the transferred assets are recorded as sales. When a transfer that qualifies as a sale is completed, we derecognize all assets transferred and recognize all assets obtained and liabilities incurred at fair value. The difference between the carrying basis of the assets transferred and the fair value of the proceeds from the sale is recorded as a component of “Investment gains, net” in our consolidated statements of operations and comprehensive income. Retained interests are primarily derived from transfers associated with our portfolio securitizations in the form of Fannie Mae MBS, REMIC certificates, guaranty assets and master servicing assets. We separately describe the subsequent accounting, as well as how we determine fair value, for our retained interests in the Fannie Mae MBS included in the “Investments in Securities” section of this note. We enter into repurchase agreements that involve contemporaneous trades to purchase and sell securities. These transactions are accounted for as secured financings since the transferor has not relinquished control over the transferred assets. These transactions are reported as securities purchased under agreements to resell and securities sold under agreements to repurchase in our consolidated balance sheets except for securities purchased under agreements to resell on an overnight basis, which are included in cash and cash equivalents in our consolidated balance sheets. Transfers of Financial Assets We issue Fannie Mae MBS through portfolio securitization transactions by transferring pools of mortgage loans or mortgage-related securities to one or more trusts or special purpose entities. We are considered to be the transferor when we transfer assets from our own retained mortgage portfolio in a portfolio securitization transaction.

Mortgage Loans (Policies)

Mortgage Loans (Policies)	12 Months Ended
	Dec. 31, 2017
Mortgage Loans on Real Estate [Abstract]
Finance, Loan and Lease Receivables, Held-for-investment, Policy [Policy Text Block]	Loans Held for Investment When we acquire mortgage loans that we have the ability and the intent to hold for the foreseeable future or until maturity, we classify the loans as HFI. When we consolidate a trust, we recognize the loans underlying the trust in our consolidated balance sheets. The trusts do not have the ability to sell mortgage loans and the use of such loans is limited exclusively to the settlement of obligations of the trusts. Therefore, mortgages acquired when we have the intent to securitize via trusts that are consolidated will generally be classified as HFI in our consolidated balance sheets both prior to and subsequent to their securitization. We report the carrying value of HFI loans at the unpaid principal balance, net of unamortized premiums and discounts, other cost basis adjustments, and allowance for loan losses. We recognize interest income on HFI loans on an accrual basis using the interest method over the contractual life of the loan, including the amortization of any deferred cost basis adjustments, such as the premium or discount at acquisition, unless we determine that the ultimate collection of contractual principal or interest payments in full is not reasonably assured. We report the carrying value of HFI loans at the unpaid principal balance, net of unamortized premiums and discounts, other cost basis adjustments, and an allowance for loan losses. We define the recorded investment of HFI loans as unpaid principal balance, net of unamortized premiums and discounts, other cost basis adjustments, and accrued interest receivable.
Finance, Loan and Lease Receivables, Held-for-sale, Policy [Policy Text Block]	Loans Held for Sale When we acquire mortgage loans that we intend to sell or securitize via trusts that will not be consolidated, we classify the loans as held for sale (“HFS”). We report the carrying value of HFS loans at the lower of cost or fair value. Any excess of an HFS loan’s cost over its fair value is recognized as a valuation allowance, with changes in the valuation allowance recognized as “Investment gains, net” in our consolidated statements of operations and comprehensive income. We recognize interest income on HFS loans on an accrual basis, unless we determine that the ultimate collection of contractual principal or interest payments in full is not reasonably assured. Purchased premiums, discounts and other cost basis adjustments on HFS loans are deferred upon loan acquisition, included in the cost basis of the loan, and not amortized. We determine any lower of cost or fair value adjustment on HFS loans at an individual loan level. In the event that we reclassify held for investment (“HFI”) loans to HFS loans, based upon a change in our intent, we record the loans at lower of cost or fair value on the date of redesignation. If the amounts charged off upon redesignation exceed the allowance related to the loans, we record a provision for credit losses. If the amounts charged off are less than the allowance related to the loans, we recognize a benefit for credit losses. We recognize recoveries of previously charged-off amounts as a reduction to charge-offs. We report the carrying value of HFS loans at the lower of cost or fair value and record valuation changes in “Investment gains, net” in our consolidated statements of operations and comprehensive income.
Troubled Debt Restructurings [Policy Text Block]	Restructured Loans A modification to the contractual terms of a loan that results in granting a concession to a borrower experiencing financial difficulties is considered a troubled debt restructuring (“TDR”). Our loss mitigation programs primarily include modifications that result in the capitalization of past due amounts in combination with interest rate reductions and/or the extension of the loan’s maturity date. Such restructurings are granted to borrowers in financial difficulty on either a permanent or contingent basis, as in the case of modifications with a trial period. We consider these types of loan restructurings to be TDRs. We generally do not include principal or past due interest forgiveness as part of our loss mitigation programs, and, as a result, we generally do not charge off any outstanding principal or accrued interest amounts at the time of loan modification. We believe that the loan underwriting activities we perform as a part of our loan modification process coupled with the borrower’s successful performance during any required trial period provide us reasonable assurance regarding the collectibility of the principal and interest due in accordance with the loan’s modified terms, which include any past due interest amounts that are capitalized as principal at the time of modification. As such, the loan is returned to accrual status when the loan modification is completed ( i.e ., at the end of the trial period), and we accrue interest thereafter in accordance with our interest accrual policy. If the loan was on nonaccrual status prior to entering the trial period, it remains on nonaccrual status until the borrower demonstrates performance via the trial period and the modification is finalized. In addition to these loan modifications, we also engage in other loss mitigation activities with troubled borrowers, which include repayment plans, forbearance arrangements, and the capitalization only of past due amounts. Repayment plans and forbearance arrangements are informal agreements with the borrower that do not result in the legal modification of the loan. For all of these activities, we consider the deferral or capitalization of three or fewer missed payments to represent only an insignificant delay, and thus not a TDR. If we defer or capitalize more than three missed payments, the delay is no longer considered insignificant, and the restructuring is accounted for as a TDR. We measure impairment of a loan restructured in a TDR individually based on the excess of the recorded investment in the loan over the present value of the expected future cash inflows discounted at the loan’s original effective interest rate. Costs incurred to complete a TDR are expensed as incurred. However, when foreclosure is probable on an individually impaired loan, we measure impairment based on the difference between our recorded investment in the loan and the fair value of the underlying property, adjusted for the estimated costs to sell the property and estimated insurance or other proceeds we expect to receive. A modification to the contractual terms of a loan that results in granting a concession to a borrower experiencing financial difficulties is considered a TDR. In addition to formal loan modifications, we also engage in other loss mitigation activities with troubled borrowers, which include repayment plans and forbearance arrangements, both of which represent informal agreements with the borrower that do not result in the legal modification of the loan’s contractual terms. We account for these informal restructurings as a TDR if we defer more than three missed payments. We also classify loans to certain borrowers who have received bankruptcy relief as TDRs.

Allowance for Loan Losses Allow

Allowance for Loan Losses Allowance For Loan Losses (Policies)	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Allowance for Loan Losses [Policy Text Block]	Allowance for Loan Losses and Reserve for Guaranty Losses Our allowance for loan losses is a valuation allowance that reflects an estimate of incurred credit losses related to our recorded investment in both single-family and multifamily HFI loans. This population includes both HFI loans held by Fannie Mae and by consolidated Fannie Mae MBS trusts. When calculating our allowance for loan losses, we consider only our net recorded investment in the loan at the balance sheet date, which includes the loan’s unpaid principal balance and any applicable cost basis adjustments. We record charge-offs as a reduction to the allowance for loan losses when losses are confirmed through the receipt of assets in satisfaction of a loan, such as the underlying collateral upon foreclosure or cash upon completion of a short sale. Additionally, we record charge-offs as a reduction to our allowance for loan losses when a loan is determined to be uncollectible, upon the redesignation of loans from HFI to HFS and pursuant to the charge-off provisions of the Advisory Bulletin. The reserve for guaranty losses is a liability account which is a component of “Other liabilities” in our consolidated balance sheets that reflects an estimate of incurred credit losses related to our guaranty to each unconsolidated Fannie Mae MBS trust that we will supplement amounts received by the Fannie Mae MBS trust as required to permit timely payments of principal and interest on the related Fannie Mae MBS and our agreements to purchase credit-impaired loans from lenders under the terms of our long-term standby commitments. As a result, the reserve for guaranty losses considers not only the principal and interest due on the loan at the current balance sheet date, but also any additional interest payments due to the trust from the current balance sheet date until the point of loan acquisition or foreclosure. We maintain an allowance for loan losses for HFI loans held by Fannie Mae and loans backing Fannie Mae MBS issued from consolidated trusts. When calculating our allowance for loan losses, we consider the unpaid principal balance, net of amortized premiums and discounts, and other cost basis adjustments of HFI loans at the balance sheet date.

Investments in Securities (Poli

Investments in Securities (Policies)	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Trading Securities, Policy [Policy Text Block]	Trading Securities Trading securities are recorded at fair value with subsequent changes in fair value recorded as “ Fair value losses, net ” in our consolidated statements of operations and comprehensive income .
Available-for-sale Securities, Policy [Policy Text Block]	Other-Than-Temporary Impairment of Debt Securities We evaluate AFS securities for other-than-temporary impairment (“OTTI”) on a quarterly basis. OTTI is considered to have occurred when the fair value of a debt security is below its amortized cost basis and we intend to sell or it is more likely than not that we will be required to sell the security before recovery. In such cases, we recognize in “Investment gains, net” in our consolidated statements of operations and comprehensive income the entire difference between the amortized cost basis of the security and its fair value. OTTI is also considered to have occurred if we do not expect to recover the entire amortized cost basis of a debt security even if we do not intend to sell the security or it is not more likely than not we will be required to sell the security before recovery. We separate the difference between the amortized cost basis of the security and its fair value into the amount representing the credit loss, which we recognize in “Investment gains, net” in our consolidated statements of operations and comprehensive income, and the amount related to all other factors, which we recognize in “Total other comprehensive loss,” net of taxes, in our consolidated statements of operations and comprehensive income. We consider guarantees, insurance contracts or other credit enhancements (such as collateral) in determining our best estimate of cash flows expected to be collected only if (1) such guarantees, insurance contracts or other credit enhancements provide for payments to be made solely to reimburse us for failure of the issuer to satisfy its required payment obligations; (2) such guarantees, insurance contracts or other credit enhancements are contractually attached to the security; and (3) collection of the amounts receivable under these agreements is deemed probable. Guarantees, insurance contracts or other credit enhancements are considered contractually attached if they are part of and trade with the security upon transfer of the security to a third party. In periods after we recognize OTTI of debt securities, we use the prospective interest method to recognize interest income. Under the prospective interest method, we calculate a new effective yield for subsequent recognition of interest income and measurement of impairment when we determine that there has been a significant increase in expected or actual cash flows. We consider a significant increase in cash flows to be at least a 10% increase over two consecutive quarters of the expected or actual cash flows. We calculate the new effective yield by using the new cost basis and the significantly increased actual or expected cash flows. Available-for-Sale Securities We record AFS securities at fair value with unrealized gains and losses, recorded net of tax, as a component of “ Other comprehensive loss ” and we recognize realized gains and losses from the sale of AFS securities in “ Investment gains, net ” in our consolidated statements of operations and comprehensive income . Other-Than-Temporary Impairments For AFS securities, OTTI is considered to have occurred when the fair value of a debt security is below its amortized cost basis and we intend to sell or it is more likely than not that we will be required to sell the security before recovery. Additionally, OTTI is considered to have occurred if we do not expect to recover the entire amortized cost basis of a debt security even if we do not intend to sell the security or it is not more likely than not we will be required to sell the security before recovery.

Derivative Instruments (Policie

Derivative Instruments (Policies)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives, Policy [Policy Text Block]	Derivative Instruments We recognize all derivatives as either assets or liabilities in our consolidated balance sheets at their fair value on a trade date basis. We report derivatives in a gain position after offsetting by counterparty in “Other assets” and derivatives in a loss position after offsetting by counterparty in “Other liabilities” in our consolidated balance sheets. • Interest rate swap contracts. An interest rate swap is a transaction between two parties in which each party agrees to exchange payments tied to different interest rates or indices for a specified period of time, generally based on a notional amount of principal. The types of interest rate swaps we use include pay-fixed swaps, receive-fixed swaps and basis swaps. • Interest rate option contracts. These contracts primarily include pay-fixed swaptions, receive-fixed swaptions, cancelable swaps and interest rate caps. A swaption is an option contract that allows us or a counterparty to enter into a pay-fixed or receive-fixed swap at some point in the future. • Foreign currency swaps. These swaps convert debt that we issue in foreign denominated currencies into U.S. dollars. We enter into foreign currency swaps only to the extent that we hold foreign currency debt. • Futures. These are standardized exchange-traded contracts that either obligate a buyer to buy an asset at a predetermined date and price or a seller to sell an asset at a predetermined date and price. The types of futures contracts we enter into include Eurodollar, U.S. Treasury and swaps.

Income Tax (Policies)

Income Tax (Policies)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Tax, Policy [Policy Text Block]	Income Taxes We recognize deferred tax assets and liabilities based on the differences in the book and tax bases of assets and liabilities. We measure deferred tax assets and liabilities using enacted tax rates that are applicable to the period(s) that the differences are expected to reverse. We adjust deferred tax assets and liabilities for the effects of changes in tax laws and rates in the period of enactment. We recognize investment and other tax credits through our effective tax rate calculation assuming that we will be able to realize the full benefit of the credits. We reduce our deferred tax assets by an allowance if, based on the weight of available positive and negative evidence, it is more likely than not (a probability of greater than 50%) that we will not realize some portion, or all, of the deferred tax asset. We recognize deferred tax assets and liabilities for future tax consequences arising from differences between the carrying amounts of existing assets and liabilities under GAAP and their respective tax bases.

Segment Reporting (Policies)

Segment Reporting (Policies)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Segment Reporting, Policy [Policy Text Block]	We have two reportable business segments: Single-Family and Multifamily. The Single-Family business operates in the secondary mortgage market relating to loans secured by properties containing four or fewer residential dwelling units. The Multifamily business operates in the secondary mortgage market relating primarily to loans secured by properties containing five or more residential units. We describe the management reporting and allocation process used to generate our segment results in “ Note 10, Segment Reporting .” We have two reportable business segments: Single-Family and Multifamily. Our CEO is the chief operating decision maker and allocates resources and assesses performance based on these two business segments. Results of our two business segments are intended to reflect each segment as if it were a stand-alone business. The sum of the results for our two business segments equals our consolidated results of operations.

Netting Arrangements (Policies)

Netting Arrangements (Policies)	12 Months Ended
	Dec. 31, 2017
Offsetting [Abstract]
Derivatives, Offsetting Policy [Policy Text Block]	We offset the carrying amounts of certain derivatives that are in gain positions and loss positions with the same counterparty as well as cash collateral receivables and payables associated with derivative positions under master netting arrangements. We offset these amounts only when we have the legal right to offset under the contract and we have met all of the offsetting conditions. We determine our rights to offset the assets and liabilities presented above with the same counterparty, including collateral posted or received, based on the contractual arrangements entered into with our individual counterparties and various rules and regulations that would govern the insolvency of a derivative counterparty. Derivative instruments are recorded at fair value and securities purchased under agreements to resell or similar arrangements are recorded at amortized cost in our consolidated balance sheets.

Fair Value (Policies)

Fair Value (Policies)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurement, Policy [Policy Text Block]	We use fair value measurements for the initial recording of certain assets and liabilities and periodic remeasurement of certain assets and liabilities on a recurring or nonrecurring basis. Fair Value Measurement Fair value measurement guidance defines fair value, establishes a framework for measuring fair value and sets forth disclosures around fair value measurements. This guidance applies whenever other accounting guidance requires or permits assets or liabilities to be measured at fair value. The guidance establishes a three-level fair value hierarchy that prioritizes the inputs into the valuation techniques used to measure fair value. The fair value hierarchy gives the highest priority, Level 1, to measurements based on unadjusted quoted prices in active markets for identical assets or liabilities. The next highest priority, Level 2, is given to measurements of assets and liabilities based on limited observable inputs or observable inputs for similar assets and liabilities. The lowest priority, Level 3, is given to measurements based on unobservable inputs. We elected the fair value option for our credit risk-sharing debt securities issued under our CAS series prior to January 1, 2016 and certain loans that contain embedded derivatives that would otherwise require bifurcation. Under the fair value option, we elected to carry these instruments at fair value instead of bifurcating the embedded derivative from such instruments. We elected the fair value option for all long-term structured debt instruments that are issued in response to specific investor demand and have interest rates that are based on a calculated index or formula and are economically hedged with derivatives at the time of issuance. By electing the fair value option for these instruments, we are able to eliminate the volatility in our results of operations that would otherwise result from the accounting asymmetry created by recording these structured debt instruments at cost while recording the related derivatives at fair value.

Commitments and Contingencies (

Commitments and Contingencies (Policies)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies: Policy [Policy Text Block]	We establish an accrual for matters when a loss is probable and we can reasonably estimate the amount of such loss. For legal actions or proceedings where the likelihood of a loss is not probable or cannot be reasonably estimated, we do not establish an accrual. On a quarterly basis, we review relevant information about all pending legal actions and proceedings for the purpose of evaluating and revising our contingencies, accruals and disclosures.
Loan and Mortgage Related Securities Commitments: Policy [Policy Text Block]	We have unconditional commitments related to the purchase of loans and mortgage-related securities. These include both on- and off-balance sheet commitments. A portion of these have been recorded as derivatives in our consolidated balance sheets.

Consolidations and Transfers 37

Consolidations and Transfers of Financial Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Consolidations and Transfers of Financial Assets [Abstract]
Unconsolidated Variable Interest Entities [Table Text Block]	The following table displays the carrying amount and classification of our assets and liabilities that relate to our involvement with unconsolidated mortgage-backed trusts. As of December 31, 2017 2016 (Dollars in millions) Assets and liabilities recorded in our consolidated balance sheets related to mortgage-backed trusts: Assets: Trading securities: Fannie Mae $ 3,809 $ 4,642 Non-Fannie Mae 1,580 3,473 Total trading securities 5,389 8,115 Available-for-sale securities: Fannie Mae 2,032 2,447 Non-Fannie Mae 2,062 4,879 Total available-for-sale securities 4,094 7,326 Other assets 74 77 Other liabilities (467 ) (528 ) Net carrying amount $ 9,090 $ 14,990

Mortgage Loans (Tables)

Mortgage Loans (Tables)	12 Months Ended
	Dec. 31, 2017
Mortgage Loans on Real Estate [Line Items]
Loans in Mortgage Portfolio [Table Text Block]	The following table displays the carrying value of our mortgage loans. As of December 31, 2017 2016 (Dollars in millions) Single-family $ 2,890,634 $ 2,833,750 Multifamily 265,069 229,896 Total unpaid principal balance of mortgage loans 3,155,703 3,063,646 Cost basis and fair value adjustments, net 41,906 39,572 Allowance for loan losses for loans held for investment (19,084 ) (23,465 ) Total mortgage loans $ 3,178,525 $ 3,079,753 The following table displays the allowance for loan losses and recorded investment in our HFI loans by impairment or allowance methodology and portfolio segment, excluding loans for which we have elected the fair value option. As of December 31, 2017 2016 Single-Family Multifamily Total Single-Family Multifamily Total (Dollars in millions) Allowance for loan losses by segment: Individually impaired loans (1) $ (17,247 ) $ (42 ) $ (17,289 ) $ (21,920 ) $ (33 ) $ (21,953 ) Collectively reserved loans (1,602 ) (193 ) (1,795 ) (1,363 ) (149 ) (1,512 ) Total allowance for loan losses $ (18,849 ) $ (235 ) $ (19,084 ) $ (23,283 ) $ (182 ) $ (23,465 ) Recorded investment in loans by segment: Individually impaired loans (1) $ 135,191 $ 590 $ 135,781 $ 155,598 $ 589 $ 156,187 Collectively reserved loans 2,787,783 266,411 3,054,194 2,708,337 231,292 2,939,629 Total recorded investment in loans $ 2,922,974 $ 267,001 $ 3,189,975 $ 2,863,935 $ 231,881 $ 3,095,816 __________ (1) Includes acquired credit-impaired loans.
Aging Analysis [Table Text Block]	The following tables display an aging analysis of the total recorded investment in our HFI mortgage loans by portfolio segment and class, excluding loans for which we have elected the fair value option. As of December 31, 2017 30 - 59 Days Delinquent 60 - 89 Days Delinquent Seriously Delinquent (1) Total Delinquent Current Total Recorded Investment in Loans 90 Days or More Delinquent and Accruing Interest Recorded Investment in Nonaccrual Loans (Dollars in millions) Single-family: Primary $ 35,582 $ 10,396 $ 23,999 $ 69,977 $ 2,732,818 $ 2,802,795 $ 87 $ 37,971 Government (2) 55 21 206 282 30,807 31,089 206 — Alt-A 3,186 1,147 3,418 7,751 59,475 67,226 5 5,094 Other 1,185 411 1,252 2,848 19,016 21,864 5 1,834 Total single-family 40,008 11,975 28,875 80,858 2,842,116 2,922,974 303 44,899 Multifamily (3) 26 N/A 276 302 266,699 267,001 — 424 Total $ 40,034 $ 11,975 $ 29,151 $ 81,160 $ 3,108,815 $ 3,189,975 $ 303 $ 45,323 As of December 31, 2016 30 - 59 Days Delinquent 60 - 89 Days Delinquent Seriously Delinquent (1) Total Delinquent Current Total Recorded Investment in Loans 90 Days or More Delinquent and Accruing Interest Recorded Investment in Nonaccrual Loans (Dollars in millions) Single-family: Primary $ 31,631 $ 7,910 $ 21,761 $ 61,302 $ 2,654,195 $ 2,715,497 $ 22 $ 33,448 Government (2) 56 22 256 334 36,814 37,148 256 — Alt-A 3,629 1,194 4,221 9,044 72,903 81,947 2 6,019 Other 1,349 438 1,582 3,369 25,974 29,343 5 2,238 Total single-family 36,665 9,564 27,820 74,049 2,789,886 2,863,935 285 41,705 Multifamily (3) 44 N/A 129 173 231,708 231,881 — 403 Total $ 36,709 $ 9,564 $ 27,949 $ 74,222 $ 3,021,594 $ 3,095,816 $ 285 $ 42,108 __________ (1) Single-family seriously delinquent loans are loans that are 90 days or more past due or in the foreclosure process. Multifamily seriously delinquent loans are loans that are 60 days or more past due. (2) Primarily consists of reverse mortgages, which due to their nature, are not aged and are included in the current column. (3) Multifamily loans 60 - 89 days delinquent are included in the seriously delinquent column.
Individually Impaired Loans [Table Text Block]	The following tables display the total unpaid principal balance, recorded investment, related allowance, average recorded investment and interest income recognized for individually impaired loans. As of December 31, 2017 2016 Unpaid Principal Balance Total Recorded Investment Related Allowance for Loan Losses Unpaid Principal Balance Total Recorded Investment Related Allowance for Loan Losses (Dollars in millions) Individually impaired loans: With related allowance recorded: Single-family: Primary $ 91,194 $ 86,864 $ (11,652 ) $ 105,113 $ 99,825 $ (14,462 ) Government 276 279 (56 ) 302 305 (59 ) Alt-A 23,077 21,045 (4,046 ) 28,599 26,059 (5,365 ) Other 8,488 8,006 (1,493 ) 11,087 10,465 (2,034 ) Total single-family 123,035 116,194 (17,247 ) 145,101 136,654 (21,920 ) Multifamily 279 280 (42 ) 320 323 (33 ) Total individually impaired loans with related allowance recorded 123,314 116,474 (17,289 ) 145,421 136,977 (21,953 ) With no related allowance recorded: (1) Single-family: Primary 16,027 15,158 — 15,733 14,758 — Government 66 60 — 63 59 — Alt-A 3,253 2,870 — 3,511 3,062 — Other 988 909 — 1,159 1,065 — Total single-family 20,334 18,997 — 20,466 18,944 — Multifamily 308 310 — 266 266 — Total individually impaired loans with no related allowance recorded 20,642 19,307 — 20,732 19,210 — Total individually impaired loans (2) $ 143,956 $ 135,781 $ (17,289 ) $ 166,153 $ 156,187 $ (21,953 ) For the Year Ended December 31, 2017 2016 2015 Average Recorded Investment Total Interest Income Recognized (3) Interest Income Recognized on a Cash Basis Average Recorded Investment Total Interest Income Recognized (3) Interest Income Recognized on a Cash Basis Average Recorded Investment Total Interest Income Recognized (3) Interest Income Recognized on a Cash Basis (Dollars in millions) Individually impaired loans: With related allowance recorded: Single-family: Primary $ 92,893 $ 3,721 $ 319 $ 105,076 $ 4,004 $ 325 $ 114,737 $ 4,190 $ 318 Government 292 10 — 314 12 — 299 12 — Alt-A 23,536 929 56 27,512 1,010 54 30,453 1,034 54 Other 9,158 318 19 11,382 365 20 12,863 376 21 Total single-family 125,879 4,978 394 144,284 5,391 399 158,352 5,612 393 Multifamily 273 9 — 508 29 — 973 16 — Total individually impaired loans with related allowance recorded 126,152 4,987 394 144,792 5,420 399 159,325 5,628 393 With no related allowance recorded: (1) Single-family: Primary 15,166 1,107 96 15,293 1,236 91 15,796 1,039 91 Government 61 3 — 59 4 — 55 4 — Alt-A 3,000 270 13 3,293 309 9 3,647 218 11 Other 997 84 4 1,116 108 3 1,259 75 3 Total single-family 19,224 1,464 113 19,761 1,657 103 20,757 1,336 105 Multifamily 297 19 — 317 13 — 442 10 — Total individually impaired loans with no related allowance recorded 19,521 1,483 113 20,078 1,670 103 21,199 1,346 105 Total individually impaired loans $ 145,673 $ 6,470 $ 507 $ 164,870 $ 7,090 $ 502 $ 180,524 $ 6,974 $ 498 __________ (1) The discounted cash flows or collateral value equals or exceeds the carrying value of the loan and, as such, no valuation allowance is required. (2) Includes single-family loans restructured in a TDR with a recorded investment of $134.7 billion and $155.0 billion as of December 31, 2017 and 2016 , respectively. Includes multifamily loans restructured in a TDR with a recorded investment of $185 million and $248 million as of December 31, 2017 and 2016 , respectively. (3) Total single-family interest income recognized of $6.4 billion for the year ended December 31, 2017 consists of $5.5 billion of contractual interest and $925 million of effective yield adjustments. Total single-family interest income recognized of $7.0 billion for the year ended December 31, 2016 consists of $5.7 billion of contractual interest and $1.3 billion of effective yield adjustments. Total single-family interest income recognized of $6.9 billion for the year ended December 31, 2015 consists of $5.7 billion of contractual interest and $1.2 billion of effective yield adjustments.
Troubled Debt Restructurings Activity [Table Text Block]	The following table displays the number of loans and recorded investment in loans restructured in a TDR. For the Year Ended December 31, 2017 2016 2015 Number of Loans Recorded Investment Number of Loans Recorded Investment Number of Loans Recorded Investment (Dollars in millions) Single-family: Primary 59,708 $ 8,247 61,586 $ 8,405 71,293 $ 9,713 Government 171 18 186 20 241 27 Alt-A 5,369 771 6,647 946 9,037 1,374 Other 1,158 207 1,381 244 1,835 333 Total single-family 66,406 9,243 69,800 9,615 82,406 11,447 Multifamily 8 99 11 66 12 40 Total TDRs 66,414 $ 9,342 69,811 $ 9,681 82,418 $ 11,487 The following table displays the number of loans and our recorded investment in these loans at the time of payment default for loans that were restructured in a TDR in the twelve months prior to the payment default. For purposes of this disclosure, we define loans that had a payment default as: single-family and multifamily loans with completed TDRs that liquidated during the period, either through foreclosure, deed-in-lieu of foreclosure or a short sale; single-family loans with completed modifications that are two or more months delinquent during the period; or multifamily loans with completed modifications that are one or more months delinquent during the period. For the Year Ended December 31, 2017 2016 2015 Number of Loans Recorded Investment Number of Loans Recorded Investment Number of Loans Recorded Investment (Dollars in millions) Single-family: Primary 19,539 $ 2,722 20,810 $ 2,938 26,206 $ 3,808 Government 91 10 95 11 118 16 Alt-A 2,588 400 3,131 500 4,128 706 Other 760 145 1,002 172 1,229 247 Total single-family 22,978 3,277 25,038 3,621 31,681 4,777 Multifamily 2 12 5 46 3 6 Total TDRs that subsequently defaulted 22,980 $ 3,289 25,043 $ 3,667 31,684 $ 4,783
Single-Family [Member]
Mortgage Loans on Real Estate [Line Items]
Credit Quality Indicators [Table Text Block]	The following table displays the total recorded investment in our single-family HFI loans by class and credit quality indicator, excluding loans for which we have elected the fair value option. As of December 31, 2017 (1) 2016 (1) Primary Alt-A Other Primary Alt-A Other (Dollars in millions) Estimated mark-to-market LTV ratio: (2) Less than or equal to 80% $ 2,439,858 $ 51,903 $ 16,428 $ 2,321,201 $ 56,250 $ 19,382 Greater than 80% and less than or equal to 90% 238,038 6,680 2,277 244,231 9,787 3,657 Greater than 90% and less than or equal to 100% 106,076 4,044 1,443 114,412 6,731 2,627 Greater than 100% 18,823 4,599 1,716 35,653 9,179 3,677 Total $ 2,802,795 $ 67,226 $ 21,864 $ 2,715,497 $ 81,947 $ 29,343 __________ (1) Excludes $31.1 billion and $37.1 billion as of December 31, 2017 and 2016 , respectively, of mortgage loans guaranteed or insured, in whole or in part, by the U.S. government or one of its agencies, that are not Alt-A loans. The segment class is primarily reverse mortgages for which we do not calculate an estimated mark-to-market LTV ratio. (2) The aggregate estimated mark-to-market LTV ratio is based on the unpaid principal balance of the loan as of the end of each reported period divided by the estimated current value of the property, which we calculate using an internal valuation model that estimates periodic changes in home value.
Multifamily [Member]
Mortgage Loans on Real Estate [Line Items]
Credit Quality Indicators [Table Text Block]	The following table displays the total recorded investment in our multifamily HFI loans by credit quality indicator, excluding loans for which we have elected the fair value option. As of December 31, 2017 2016 (Dollars in millions) Credit risk profile by internally assigned grade: Non-classified $ 263,416 $ 228,749 Classified: (1) Substandard 3,585 3,129 Doubtful — 3 Total classified 3,585 3,132 Total $ 267,001 $ 231,881 __________ (1) A loan classified as “Substandard” has a well-defined weakness that jeopardizes the timely full repayment. “Doubtful” refers to a loan with a weakness that makes collection or liquidation in full highly questionable and improbable based on existing conditions and values.

Allowance for Loan Losses (Tabl

Allowance for Loan Losses (Tables)	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Allowance for Loan Losses Roll Forward by Segment [Table Text Block]	The following table displays changes in single-family, multifamily and total allowance for loan losses. As of December 31, 2017 2016 2015 (Dollars in millions) Single-family allowance for loan losses: Beginning balance $ (23,283 ) $ (27,709 ) $ (35,177 ) Benefit for loan losses (1) 1,994 1,704 68 Charge-offs (2) 2,795 3,254 9,731 Recoveries (326 ) (442 ) (1,136 ) Other (3) (29 ) (90 ) (1,195 ) Ending balance $ (18,849 ) $ (23,283 ) $ (27,709 ) Multifamily allowance for loan losses: Beginning balance $ (182 ) $ (242 ) $ (364 ) Benefit (provision) for loan losses (1) (53 ) 55 90 Charge-offs (2) 3 12 43 Recoveries (3 ) (7 ) (4 ) Other (3) — — (7 ) Ending balance $ (235 ) $ (182 ) $ (242 ) Total allowance for loan losses: Beginning balance $ (23,465 ) $ (27,951 ) $ (35,541 ) Benefit for loan losses (1) 1,941 1,759 158 Charge-offs (2) 2,798 3,266 9,774 Recoveries (329 ) (449 ) (1,140 ) Other (3) (29 ) (90 ) (1,202 ) Ending balance $ (19,084 ) $ (23,465 ) $ (27,951 ) __________ (1) Benefit (provision) for loan losses is included in “ Benefit for credit losses ” in our consolidated statements of operations and comprehensive income. (2) For the year ended December 31, 2015, includes charge-offs of (1) $1.8 billion in loans held for investment and $724 million in preforeclosure property taxes and insurance receivable in connection with our adoption of the Advisory Bulletin on January 1, 2015 and (2) $1.1 billion in accrued interest receivable in connection with our adoption of a change in accounting policy on January 1, 2015 related to the treatment of interest previously accrued, but not collected, at the date that loans are placed on nonaccrual status. (3) Amounts represent changes in other loss reserves which are reflected in benefit (provision) for loan losses, charge-offs, and recoveries.
Allowance for Loan Losses and Total Recorded Investment in HFI Loans [Table Text Block]	The following table displays the carrying value of our mortgage loans. As of December 31, 2017 2016 (Dollars in millions) Single-family $ 2,890,634 $ 2,833,750 Multifamily 265,069 229,896 Total unpaid principal balance of mortgage loans 3,155,703 3,063,646 Cost basis and fair value adjustments, net 41,906 39,572 Allowance for loan losses for loans held for investment (19,084 ) (23,465 ) Total mortgage loans $ 3,178,525 $ 3,079,753 The following table displays the allowance for loan losses and recorded investment in our HFI loans by impairment or allowance methodology and portfolio segment, excluding loans for which we have elected the fair value option. As of December 31, 2017 2016 Single-Family Multifamily Total Single-Family Multifamily Total (Dollars in millions) Allowance for loan losses by segment: Individually impaired loans (1) $ (17,247 ) $ (42 ) $ (17,289 ) $ (21,920 ) $ (33 ) $ (21,953 ) Collectively reserved loans (1,602 ) (193 ) (1,795 ) (1,363 ) (149 ) (1,512 ) Total allowance for loan losses $ (18,849 ) $ (235 ) $ (19,084 ) $ (23,283 ) $ (182 ) $ (23,465 ) Recorded investment in loans by segment: Individually impaired loans (1) $ 135,191 $ 590 $ 135,781 $ 155,598 $ 589 $ 156,187 Collectively reserved loans 2,787,783 266,411 3,054,194 2,708,337 231,292 2,939,629 Total recorded investment in loans $ 2,922,974 $ 267,001 $ 3,189,975 $ 2,863,935 $ 231,881 $ 3,095,816 __________ (1) Includes acquired credit-impaired loans.

Investments in Securities (Tabl

Investments in Securities (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Investments In Trading Securities [Table Text Block]	The following table displays our investments in trading securities. As of December 31, 2017 2016 (Dollars in millions) Mortgage-related securities: Fannie Mae $ 3,876 $ 4,769 Other agency 1,118 2,058 Alt-A and subprime private-label securities 453 636 Commercial mortgage-backed securities (“CMBS”) 9 761 Mortgage revenue bonds 1 21 Total mortgage-related securities 5,457 8,245 U.S. Treasury securities 29,222 32,317 Total trading securities $ 34,679 $ 40,562
Schedule of Trading Securities Gains (Losses), Net [Table Text Block]	The following table displays information about our net trading gains and losses. For the Year Ended December 31, 2017 2016 2015 (Dollars in millions) Net trading gains (losses) $ 190 $ 28 $ (368 ) Net trading gains (losses) recognized in the period related to securities still held at period end 161 (19 ) (453 )
Schedule of Available-for-sale Securities Realized Gain (Loss) [Table Text Block]	The following table displays the gross realized gains, losses and proceeds on sales of AFS securities. For the Year Ended December 31, 2017 2016 2015 (Dollars in millions) Gross realized gains $ 487 $ 1,043 $ 1,066 Gross realized losses 1 17 70 Total proceeds (excludes initial sale of securities from new portfolio securitizations) 1,780 10,993 8,023
Schedule of Available-for-sale Securities Reconciliation [Table Text Block]	The following tables display the amortized cost, gross unrealized gains and losses, and fair value by major security type for AFS securities. As of December 31, 2017 Total Amortized Cost (1) Gross Unrealized Gains Gross Unrealized Losses (2) Total Fair Value (Dollars in millions) Fannie Mae $ 2,044 $ 102 $ (27 ) $ 2,119 Other agency 332 25 — 357 Alt-A and subprime private-label securities 662 652 — 1,314 CMBS 15 — — 15 Mortgage revenue bonds 655 20 (4 ) 671 Other mortgage-related securities 350 17 — 367 Total $ 4,058 $ 816 $ (31 ) $ 4,843 As of December 31, 2016 Total Amortized Cost (1) Gross Unrealized Gains Gross Unrealized Losses (2) Total Fair Value (Dollars in millions) Fannie Mae $ 2,445 $ 137 $ (28 ) $ 2,554 Other agency 508 39 — 547 Alt-A and subprime private-label securities 1,817 895 (3 ) 2,709 CMBS 815 4 — 819 Mortgage revenue bonds 1,245 36 (9 ) 1,272 Other mortgage-related securities 431 31 — 462 Total $ 7,261 $ 1,142 $ (40 ) $ 8,363 s __________ (1) Amortized cost consists of unpaid principal balance, unamortized premiums, discounts and other cost basis adjustments, as well as OTTI recognized in “Investment gains, net” in our consolidated statements of operations and comprehensive income. (2) Represents the gross unrealized losses on securities for which we have not recognized OTTI, as well as the noncredit component of OTTI and cumulative changes in fair value of securities for which we previously recognized the credit component of OTTI in “Accumulated other comprehensive income” in our consolidated balance sheets.
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Table Text Block]	The following tables display additional information regarding gross unrealized losses and fair value by major security type for AFS securities in an unrealized loss position. As of December 31, 2017 Less Than 12 Consecutive Months 12 Consecutive Months or Longer Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value (Dollars in millions) Fannie Mae $ (1 ) $ 134 $ (26 ) $ 461 Mortgage revenue bonds — — (4 ) 3 Total $ (1 ) $ 134 $ (30 ) $ 464 As of December 31, 2016 Less Than 12 Consecutive Months 12 Consecutive Months or Longer Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value (Dollars in millions) Fannie Mae $ (2 ) $ 139 $ (26 ) $ 477 Alt-A and subprime private-label securities — — (3 ) 73 Mortgage revenue bonds (7 ) 78 (2 ) 6 Total $ (9 ) $ 217 $ (31 ) $ 556
Investments Classified by Contractual Maturity Date [Table Text Block]	The following table displays the amortized cost and fair value of our AFS securities by major security type and remaining contractual maturity, assuming no principal prepayments. The contractual maturity of mortgage-backed securities is not a reliable indicator of their expected life because borrowers generally have the right to prepay their obligations at any time. As of December 31, 2017 Total Amortized Cost Total Fair Value One Year or Less After One Year Through Five Years After Five Years Through Ten Years After Ten Years Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value (Dollars in millions) Fannie Mae $ 2,044 $ 2,119 $ 2 $ 2 $ 12 $ 12 $ 59 $ 63 $ 1,971 $ 2,042 Other agency 332 357 2 2 15 15 57 61 258 279 Alt-A and subprime private-label securities 662 1,314 — — — — — — 662 1,314 CMBS 15 15 15 15 — — — — — — Mortgage revenue bonds 655 671 15 15 75 75 83 85 482 496 Other mortgage-related securities 350 367 — — — — 5 5 345 362 Total $ 4,058 $ 4,843 $ 34 $ 34 $ 102 $ 102 $ 204 $ 214 $ 3,718 $ 4,493 Weighted average yield (1) 6.84 % 4.18 % 6.60 % 6.59 % 6.88 % __________ (1) Yields are determined by dividing interest income (including amortization and accretion of premiums, discounts and other cost basis adjustments) by amortized cost balances as of year-end. Yields on tax-exempt obligations have been computed on a tax equivalent basis.

Financial Guarantees (Tables)

Financial Guarantees (Tables)	12 Months Ended
	Dec. 31, 2017
Guarantees [Abstract]
Financial Guarantees and Maximum Recovery [Table Text Block]	The following table displays our off-balance sheet maximum exposure, guaranty obligation recognized in our consolidated balance sheets and the potential maximum recovery from third parties through available credit enhancements and recourse related to our financial guarantees. As of December 31, 2017 2016 Maximum Exposure Guaranty Obligation Maximum Recovery (1) Maximum Exposure Guaranty Obligation Maximum Recovery (1) (Dollars in millions) Unconsolidated Fannie Mae MBS $ 10,876 $ 127 $ 7,340 $ 12,607 $ 143 $ 8,048 Other guaranty arrangements (2) 14,265 131 2,404 15,335 137 2,663 Total $ 25,141 $ 258 $ 9,744 $ 27,942 $ 280 $ 10,711 __________ (1) Recoverability of such credit enhancements and recourse is subject to, among other factors, our mortgage insurers’ and financial guarantors’ ability to meet their obligations to us. For information on our mortgage insurers and financial guarantors, see “ Note 13, Concentrations of Credit Risk .” (2) Primarily consists of credit enhancements and long-term standby commitments.

Short-Term and Long-Term Debt (

Short-Term and Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Short-Term Debt [Table Text Block]	The following table displays our outstanding short-term debt (borrowings with an original contractual maturity of one year or less) and weighted-average interest rates of these borrowings. As of December 31, 2017 2016 Outstanding Weighted- Average Interest Rate (1) Outstanding Weighted- Average Interest Rate (1) (Dollars in millions) Short-term debt of Fannie Mae $ 33,377 1.18 % $ 34,995 0.49 % Debt of consolidated trusts 379 1.11 584 0.48 Total short-term debt $ 33,756 1.18 % $ 35,579 0.49 % __________ (1) Includes the effects of discounts, premiums and other cost basis adjustments.
Long-Term Debt [Table Text Block]	The following table displays our outstanding long-term debt. As of December 31, 2017 2016 Maturities Outstanding Weighted- Average Interest Rate (1) Maturities Outstanding Weighted- Average Interest Rate (1) (Dollars in millions) Senior fixed: Benchmark notes and bonds 2018 - 2030 $ 123,541 2.11 % 2017 - 2030 $ 153,983 2.16 % Medium-term notes (2) 2018 - 2026 75,901 1.41 2017 - 2026 82,230 1.40 Other (3) 2018 - 2038 7,421 4.84 2017 - 2038 12,800 6.74 Total senior fixed 206,863 1.95 249,013 2.14 Senior floating: Medium-term notes (2) 2018 - 2020 8,425 1.36 2017 - 2019 21,476 0.71 Connecticut Avenue Securities (4) 2023 - 2030 22,527 5.18 2023 - 2029 16,511 4.77 Other (5) 2020 - 2037 376 6.36 2020 - 2037 346 6.75 Total senior floating 31,328 4.14 38,333 2.48 Subordinated debentures 2019 5,106 9.93 2019 4,645 9.93 Secured borrowings (6) 2021 - 2022 78 1.70 2021 - 2022 111 1.44 Total long-term debt of Fannie Mae (7) 243,375 2.40 292,102 2.31 Debt of consolidated trusts 2018 - 2057 3,052,923 2.80 2017 - 2056 2,934,635 2.57 Total long-term debt $ 3,296,298 2.77 % $ 3,226,737 2.54 % __________ (1) Includes the effects of discounts, premiums and other cost basis adjustments. (2) Includes long-term debt with an original contractual maturity of greater than 1 year and up to 10 years, excluding zero-coupon debt. (3) Includes other long-term debt with an original contractual maturity of greater than 10 years and foreign exchange bonds. (4) Credit risk-sharing securities that transfer a portion of the credit risk on specified pools of single-family mortgage loans to the investors in these securities, a portion of which is reported at fair value. (5) Consists of structured debt instruments that are reported at fair value. (6) Represents our remaining liability resulting from the transfer of financial assets from our consolidated balance sheets that did not qualify as a sale under the accounting guidance for the transfer of financial instruments. (7) Includes unamortized discounts and premiums, other cost basis adjustments and fair value adjustments of $752 million and $1.8 billion as of December 31, 2017 and 2016 , respectively.
Long-Term Debt by Year of Maturity [Table Text Block]	The following table displays the amount of our long-term debt as of December 31, 2017 by year of maturity for each of the years 2018 through 2022 and thereafter. The first column assumes that we pay off this debt at maturity or on the call date if the call has been announced, while the second column assumes that we redeem our callable debt at the next available call date. Long-Term Debt by Year of Maturity Assuming Callable Debt Redeemed at Next Available Call Date (Dollars in millions) 2018 $ 53,932 $ 100,446 2019 61,760 45,015 2020 39,712 25,202 2021 23,945 14,184 2022 8,463 7,353 Thereafter 55,563 51,175 Total debt of Fannie Mae (1) 243,375 243,375 Debt of consolidated trusts (2) 3,052,923 3,052,923 Total long-term debt $ 3,296,298 $ 3,296,298 __________ (1) Includes unamortized discounts and premiums, other cost basis adjustments and fair value adjustments of $752 million . (2) Contractual maturity of debt of consolidated trusts is not a reliable indicator of expected maturity because borrowers of the underlying loans generally have the right to prepay their obligations at any time.

Derivative Instruments (Tables)

Derivative Instruments (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Notional and Fair Value Position [Table Text Block]	The following table displays the notional amount and estimated fair value of our asset and liability derivative instruments. As of December 31, 2017 As of December 31, 2016 Asset Derivatives Liability Derivatives Asset Derivatives Liability Derivatives Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value (Dollars in millions) Risk management derivatives: Swaps: Pay-fixed $ 52,732 $ 772 $ 70,211 $ (2,120 ) $ 29,540 $ 660 $ 94,584 $ (4,396 ) Receive-fixed 31,671 2,391 138,852 (1,764 ) 30,207 2,696 135,470 (1,552 ) Basis 873 124 — — 1,624 115 15,600 (11 ) Foreign currency 234 59 236 (56 ) 214 40 216 (85 ) Swaptions: Pay-fixed 9,750 95 4,000 (20 ) 9,600 241 4,850 (82 ) Receive-fixed 250 13 9,250 (304 ) — — 10,100 (257 ) Other (1) 13,240 22 7,315 (1 ) 15,087 33 655 (2 ) Total gross risk management derivatives 108,750 3,476 229,864 (4,265 ) 86,272 3,785 261,475 (6,385 ) Accrued interest receivable (payable) — 835 — (814 ) — 785 — (937 ) Netting adjustment (2) — (4,272 ) — 4,979 — (4,514 ) — 6,844 Total net risk management derivatives $ 108,750 $ 39 $ 229,864 $ (100 ) $ 86,272 $ 56 $ 261,475 $ (478 ) Mortgage commitment derivatives: Mortgage commitments to purchase whole loans $ 4,143 $ 9 $ 1,570 $ (2 ) $ 4,753 $ 28 $ 3,039 $ (49 ) Forward contracts to purchase mortgage-related securities 45,925 108 21,099 (21 ) 31,635 198 27,297 (388 ) Forward contracts to sell mortgage-related securities 19,320 15 85,556 (205 ) 34,103 405 47,645 (300 ) Total mortgage commitment derivatives 69,388 132 108,225 (228 ) 70,491 631 77,981 (737 ) Derivatives at fair value $ 178,138 $ 171 $ 338,089 $ (328 ) $ 156,763 $ 687 $ 339,456 $ (1,215 ) __________ (1) Includes futures and swap credit enhancements, as well as credit risk transfer transactions and mortgage insurance contracts that we account for as derivatives. (2) The netting adjustment represents the effect of the legal right to offset under legally enforceable master netting arrangements to settle with the same counterparty on a net basis, including cash collateral posted and received. Cash collateral posted was $1.4 billion and $2.9 billion as of December 31, 2017 and 2016 , respectively. Cash collateral received was $649 million and $535 million as of December 31, 2017 and 2016 , respectively.
Fair Value Gain (Loss), Net [Table Text Block]	The following table displays, by type of derivative instrument, the fair value gains and losses, net on our derivatives. For the Year Ended December 31, 2017 2016 2015 (Dollars in millions) Risk management derivatives: Swaps: Pay-fixed $ 1,296 $ 757 $ (746 ) Receive-fixed (851 ) (751 ) 625 Basis 21 (21 ) 4 Foreign currency 49 (76 ) (60 ) Swaptions: Pay-fixed (161 ) 163 135 Receive-fixed (60 ) (230 ) (93 ) Other 13 160 (25 ) Net accrual of periodic settlements (889 ) (1,125 ) (960 ) Total risk management derivatives fair value losses, net (582 ) (1,123 ) (1,120 ) Mortgage commitment derivatives fair value gains (losses), net (603 ) 288 (393 ) Total derivatives fair value losses, net $ (1,185 ) $ (835 ) $ (1,513 )

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	The following table displays the components of our provision for federal income taxes. For the Year Ended December 31, 2017 2016 2015 (Dollars in millions) Current income tax benefit (provision) $ 600 $ (2,014 ) $ 271 Deferred income tax provision (1) (16,584 ) (4,006 ) (5,524 ) Provision for federal income taxes $ (15,984 ) $ (6,020 ) $ (5,253 ) __________ (1) Amount excludes the current income tax effect of items recognized directly in “Fannie Mae stockholders’ equity (deficit).”
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	The following table displays the difference between the statutory corporate tax rate and our effective tax rate. For the Year Ended December 31, 2017 2016 2015 Statutory corporate tax rate 35.0 % 35.0 % 35.0 % Equity investments in affordable housing projects (1.4 ) (1.9 ) (2.6 ) Effect of corporate tax rate change 53.6 — — Other (0.6 ) (0.3 ) 0.9 Valuation allowance — — (0.9 ) Effective tax rate 86.6 % 32.8 % 32.4 %
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]	The following table displays our deferred tax assets and deferred tax liabilities. The deferred tax assets and liabilities as of December 31, 2016 were measured at the applicable statutory corporate tax rate of 35% for the period. The deferred tax assets and liabilities as of December 31, 2017 have been remeasured using the 21% statutory corporate tax rate enacted in the fourth quarter of 2017 with an effective date of January 1, 2018. As of December 31, 2017 2016 (Dollars in millions) Deferred tax assets: Mortgage and mortgage-related assets $ 10,397 $ 17,130 Allowance for loan losses and basis in acquired property, net 2,286 9,496 Debt and derivative instruments 1,205 2,989 Partnership credits 1,695 1,968 Partnership and other equity investments 311 667 Other, net 1,621 1,665 Total deferred tax assets 17,515 33,915 Deferred tax liabilities: Unrealized gains on AFS securities, net 165 385 Total deferred tax liabilities 165 385 Deferred tax assets, net $ 17,350 $ 33,530
Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block]	The following table displays the changes in our unrecognized tax benefits. For the Year Ended December 31, 2017 2016 2015 (Dollars in millions) Unrecognized tax benefits as of January 1 $ — $ — $ 213 Gross increases—tax positions in current year 514 — — Gross decreases—tax positions in prior years — — (213 ) Unrecognized tax benefits as of December 31 (1) $ 514 $ — $ — __________ (1) Amount excludes tax credits of $220 million as of December 31, 2017 . We had $514 million of unrecognized tax benefits as of December 31, 2017 . If these positions were to resolve favorably, our effective tax would be reduced in future periods by $205 million . We had no unrecognized tax benefits as of December 31, 2016 or December 31, 2015.

Segment Reporting (Tables)

Segment Reporting (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Total assets by segment [Table Text Block]	The following table displays total assets by segment. As of December 31, 2017 2016 2015 (Dollars in millions) Single-Family $ 3,057,904 $ 3,029,727 $ 2,993,495 Multifamily 287,625 258,241 228,422 Total assets $ 3,345,529 $ 3,287,968 $ 3,221,917
Segment results [Table Text Block]	The following tables display our segment results. For the Year Ended December 31, 2017 Single-Family Multifamily Total (Dollars in millions) Net interest income (1) $ 18,212 $ 2,521 $ 20,733 Fee and other income (2) 1,378 849 2,227 Net revenues 19,590 3,370 22,960 Investment gains, net (3) 1,352 170 1,522 Fair value losses, net (4) (1,188 ) (23 ) (1,211 ) Administrative expenses (2,391 ) (346 ) (2,737 ) Credit-related income (expense): (5) Benefit (provision) for credit losses 2,090 (49 ) 2,041 Foreclosed property income (expense) (540 ) 19 (521 ) Total credit-related income (expense) 1,550 (30 ) 1,520 TCCA fees (6) (2,096 ) — (2,096 ) Other expenses, net (1,004 ) (507 ) (1,511 ) Income before federal income taxes 15,813 2,634 18,447 Provision for federal income taxes (14,301 ) (1,683 ) (15,984 ) Net income $ 1,512 $ 951 $ 2,463 For the Year Ended December 31, 2016 Single-Family Multifamily Total (Dollars in millions) Net interest income (1) $ 19,010 $ 2,285 $ 21,295 Fee and other income (2) 521 445 966 Net revenues 19,531 2,730 22,261 Investment gains, net (3) 944 312 1,256 Fair value losses, net (4) (1,040 ) (41 ) (1,081 ) Administrative expenses (2,418 ) (323 ) (2,741 ) Credit-related income: (5) Benefit for credit losses 2,092 63 2,155 Foreclosed property income (expense) (653 ) 9 (644 ) Total credit-related income 1,439 72 1,511 TCCA fees (6) (1,845 ) — (1,845 ) Other expenses, net (1,012 ) (16 ) (1,028 ) Income before federal income taxes 15,599 2,734 18,333 Provision for federal income taxes (5,417 ) (603 ) (6,020 ) Net income $ 10,182 $ 2,131 $ 12,313 For the Year Ended December 31, 2015 Single-Family Multifamily Total (Dollars in millions) Net interest income (1) $ 19,301 $ 2,108 $ 21,409 Fee and other income (2) 636 712 1,348 Net revenues 19,937 2,820 22,757 Investment gains, net (3) 970 366 1,336 Fair value losses, net (4) (1,505 ) (262 ) (1,767 ) Administrative expenses (2,711 ) (339 ) (3,050 ) Credit-related income (expense): (5) Benefit for credit losses 688 107 795 Foreclosed property income (expense) (1,723 ) 94 (1,629 ) Total credit-related income (expense) (1,035 ) 201 (834 ) TCCA fees (6) (1,621 ) — (1,621 ) Other income (expenses), net (831 ) 218 (613 ) Income before federal income taxes 13,204 3,004 16,208 Provision for federal income taxes (4,593 ) (660 ) (5,253 ) Net income 8,611 2,344 10,955 Less: Net income attributable to noncontrolling interest — (1 ) (1 ) Net income attributable to Fannie Mae $ 8,611 $ 2,343 $ 10,954 __________ (1) Net interest income primarily consists of guaranty fees received as compensation for assuming and managing the credit risk on loans underlying Fannie Mae MBS held by third parties for the respective business segment, and the difference between the interest income earned on the respective business segment’s mortgage assets in our retained mortgage portfolio and the interest expense associated with the debt funding those assets. Revenues from single-family guaranty fees include revenues generated by the 10 basis point increase in guaranty fees we implemented in 2012 pursuant to TCCA. (2) Single-Family fee and other income primarily consists of compensation for engaging in structured transactions and providing other lender services, and income resulting from settlement agreements resolving certain claims relating to private-label securities we purchased or that we have guaranteed. Multifamily fee and other income consists of fees associated with multifamily business activities, including yield maintenance income. (3) Investment gains and losses primarily consists of gains and losses on the sale of mortgage assets for the respective business segment. (4) Single-Family fair value gains and losses primarily consist of fair value gains and losses on risk management and mortgage commitment derivatives, trading securities and other financial instruments associated with our single-family total book of business. Multifamily fair value gains and losses primarily consist of fair value gains and losses on MBS commitment derivatives, trading securities and other financial instruments associated with our multifamily total book of business. (5) Credit-related income or expense is based on the guaranty book of business of the respective business segment and consists of the applicable segment’s benefit or provision for credit losses and foreclosed property expense on loans underlying the segment’s guaranty book of business. (6) Consists of the portion of our single-family guaranty fees that is remitted to Treasury pursuant to the TCCA.

Equity (Deficit) (Tables)

Equity (Deficit) (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Preferred Stock [Table Text Block]	The following table displays our senior preferred stock and preferred stock outstanding. Issued and Outstanding as of December 31, Annual Dividend Rate as of December 31, 2017 2017 2016 Stated Value per Share Title Issue Date Shares Amount Shares Amount Redeemable on or After (Dollars and shares in millions, except per share amounts) Senior Preferred Stock Series 2008-2 September 8, 2008 1 $ 117,149 1 $ 117,149 $ 117,149 (1) N/A (2) N/A (3) Preferred Stock Series D September 30, 1998 3 $ 150 3 $ 150 $ 50 5.250 % September 30, 1999 Series E April 15, 1999 3 150 3 150 50 5.100 April 15, 2004 Series F March 20, 2000 14 690 14 690 50 0.730 (4) March 31, 2002 (5) Series G August 8, 2000 6 288 6 288 50 0.610 (6) September 30, 2002 (5) Series H April 6, 2001 8 400 8 400 50 5.810 April 6, 2006 Series I October 28, 2002 6 300 6 300 50 5.375 October 28, 2007 Series L April 29, 2003 7 345 7 345 50 5.125 April 29, 2008 Series M June 10, 2003 9 460 9 460 50 4.750 June 10, 2008 Series N September 25, 2003 5 225 5 225 50 5.500 September 25, 2008 Series O December 30, 2004 50 2,500 50 2,500 50 7.000 (7) December 31, 2007 Convertible Series 2004-I (8) December 30, 2004 — 2,492 — 2,492 100,000 5.375 January 5, 2008 Series P September 28, 2007 40 1,000 40 1,000 25 4.500 (9) September 30, 2012 Series Q October 4, 2007 15 375 15 375 25 6.750 September 30, 2010 Series R (10) November 21, 2007 21 530 21 530 25 7.625 November 21, 2012 Series S December 11, 2007 280 7,000 280 7,000 25 7.750 (11) December 31, 2010 (12) Series T (13) May 19, 2008 89 2,225 89 2,225 25 8.250 May 20, 2013 Total 556 $ 19,130 556 $ 19,130 __________ (1) Initial stated value per share was $1,000 . Based on our draws of funds under the senior preferred stock purchase agreement with Treasury, the stated value per share on December 31, 2017 was $117,149 . (2) Beginning in 2013, dividends on the senior preferred stock are calculated based on our net worth as of the end of the immediately preceding fiscal quarter less an applicable capital reserve amount. The applicable capital reserve amount was $600 million for each dividend period in 2017; however, the dividend payment for the fourth quarter of 2017 was reduced by $2.4 billion from the otherwise payable amount pursuant to the December 2017 letter agreement with Treasury. For each dividend period beginning in 2018, the applicable capital reserve amount will be $3.0 billion . (3) Any liquidation preference of our senior preferred stock in excess of $1.0 billion may be repaid through an issuance of common or preferred stock, which would require the consent of the conservator and Treasury. The initial $1.0 billion liquidation preference may be repaid only in conjunction with termination of Treasury’s funding commitment under the senior preferred stock purchase agreement. (4) Rate effective March 31, 2016. Variable dividend rate resets every two years at a per annum rate equal to the two-year Constant Maturity U.S. Treasury Rate (“CMT”) minus 0.16% with a cap of 11% per year. (5) Represents initial call date. Redeemable every two years thereafter. (6) Rate effective September 30, 2016. Variable dividend rate resets every two years at a per annum rate equal to the two-year CMT rate minus 0.18% with a cap of 11% per year. (7) Rate effective December 31, 2017 . Variable dividend rate resets quarterly thereafter at a per annum rate equal to the greater of 7.00% or 10-year CMT rate plus 2.375% . (8) Issued and outstanding shares were 24,922 as of December 31, 2017 and 2016 . (9) Rate effective December 31, 2017 . Variable dividend rate resets quarterly thereafter at a per annum rate equal to the greater of 4.50% or 3-Month LIBOR plus 0.75% . (10) On November 21, 2007, we issued 20 million shares of preferred stock in the amount of $500 million . Subsequent to the initial issuance, we issued an additional 1.2 million shares in the amount of $30 million on December 14, 2007 under the same terms as the initial issuance. (11) Rate effective December 31, 2017 . Variable dividend rate resets quarterly thereafter at a per annum rate equal to the greater of 7.75% or 3-Month LIBOR plus 4.23% . (12) Represents initial call date. Redeemable every five years thereafter. (13) On May 19, 2008, we issued 80 million shares of preferred stock in the amount of $2.0 billion . Subsequent to the initial issuance, we issued an additional 8 million shares in the amount of $200 million on May 22, 2008 and 1 million shares in the amount of $25 million on June 4, 2008 under the same terms as the initial issuance.
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	The following table displays our accumulated other comprehensive income, net of tax, by major categories. As of December 31, 2017 2016 2015 (Dollars in millions) Net unrealized gains on AFS securities for which we have not recorded OTTI $ 87 $ 135 $ 455 Net unrealized gains on AFS securities for which we have recorded OTTI 423 581 903 Other 43 43 49 Accumulated other comprehensive income $ 553 $ 759 $ 1,407 The following table displays changes in accumulated other comprehensive income, net of tax. For the Year Ended December 31, 2017 2016 AFS (1) Other Total AFS (1) Other Total (Dollars in millions) Beginning balance $ 716 $ 43 $ 759 $ 1,358 $ 49 $ 1,407 Other comprehensive income (loss) before reclassifications 53 8 61 (55 ) 2 (53 ) Amounts reclassified from other comprehensive income (259 ) (8 ) (267 ) (587 ) (8 ) (595 ) Net other comprehensive loss (206 ) — (206 ) (642 ) (6 ) (648 ) Ending balance $ 510 $ 43 $ 553 $ 716 $ 43 $ 759 __________ (1) The amounts reclassified from accumulated other comprehensive income represent the gain or loss recognized in earnings due to a sale of an AFS security or the recognition of a net impairment recognized in earnings, which are recorded in “ Investment gains, net ” in our consolidated statements of operations and comprehensive income.

Regulatory Capital Requiremen47

Regulatory Capital Requirements (Tables)	12 Months Ended
	Dec. 31, 2017
Regulatory Capital Requirements [Abstract]
Regulatory Capital Classification Measures [Table Text Block]	The following table displays our regulatory capital classification measures. As of December 31, 2017 2016 (Dollars in millions) Core capital (1) $ (121,389 ) $ (111,836 ) Statutory minimum capital requirement (2) 23,007 24,351 Deficit of core capital over statutory minimum capital requirement $ (144,396 ) $ (136,187 ) __________ (1) The sum of (a) the stated value of our outstanding common stock (common stock less treasury stock); (b) the stated value of our outstanding non-cumulative perpetual preferred stock; (c) our paid-in capital; and (d) our retained earnings (accumulated deficit). Core capital does not include: (a) accumulated other comprehensive income or (b) senior preferred stock. (2) Generally, the sum of (a) 2.50% of on-balance sheet assets, except those underlying Fannie Mae MBS held by third parties; (b) 0.45% of the unpaid principal balance of outstanding Fannie Mae MBS held by third parties; and (c) up to 0.45% of other off-balance sheet obligations, which may be adjusted by the Director of FHFA under certain circumstances.

Concentrations of Credit Risk (

Concentrations of Credit Risk (Tables)	12 Months Ended
	Dec. 31, 2017
Geographic Concentration Risk [Member]
Concentration Risk [Line Items]
Schedules of Concentration of Risk, by Risk Factor [Table Text Block]	The following table displays the regional geographic concentration of single-family and multifamily loans in our guaranty book of business, measured by the unpaid principal balance of the loans. Geographic Concentration (1) Percentage of Single-Family Conventional Guaranty Book of Business (2) Percentage of Multifamily Guaranty Book of Business (3) As of December 31, As of December 31, 2017 2016 2017 2016 Midwest 15 % 15 % 9 % 9 % Northeast 18 18 15 16 Southeast 22 22 26 25 Southwest 17 17 23 22 West 28 28 27 28 Total 100 % 100 % 100 % 100 % __________ (1) Midwest consists of IL, IN, IA, MI, MN, NE, ND, OH, SD, WI; Northeast consists of CT, DE, ME, MA, NH, NJ, NY, PA, PR, RI, VT, VI; Southeast consists of AL, DC, FL, GA, KY, MD, MS, NC, SC, TN, VA, WV; Southwest consists of AZ, AR, CO, KS, LA, MO, NM, OK, TX, UT; West consists of AK, CA, GU, HI, ID, MT, NV, OR, WA and WY. (2) Consists of the portion of our single-family conventional guaranty book of business for which we have detailed loan level information, which constituted over 99% of our total single-family conventional guaranty book of business as of December 31, 2017 and 2016 . (3) Consists of the portion of our multifamily guaranty book of business for which we have detailed loan level information, which constituted 99% of our total multifamily guaranty book of business as of December 31, 2017 and 2016 .
Single-Family [Member]
Concentration Risk [Line Items]
Schedule of Delinquency Status Guaranty Book of Business [Table Text Block]	The following tables display the delinquency status and serious delinquency rates for specified loan categories of our single-family conventional and total multifamily guaranty book of business. As of December 31, 2017 (1) 2016 (1) 30 Days Delinquent 60 Days Delinquent Seriously Delinquent (2) 30 Days Delinquent 60 Days Delinquent Seriously Delinquent (2) Percentage of single-family conventional guaranty book of business (3) 1.42 % 0.43 % 1.15 % 1.30 % 0.36 % 1.18 % Percentage of single-family conventional loans (4) 1.63 0.50 1.24 1.51 0.41 1.20
Schedule of Risk Characteristics Guaranty Book of Business [Table Text Block]	As of December 31, 2017 (1) 2016 (1) Percentage of (3) Seriously Delinquent Rate (2) Percentage of (3) Seriously Delinquent Rate (2) Estimated mark-to-market loan-to-value ratio: Greater than 100% 1 % 11.70 % 2 % 10.44 % Geographical distribution: California 19 0.42 19 0.50 Florida 6 3.71 6 1.89 New Jersey 4 2.15 4 3.07 New York 5 2.02 5 2.65 All other states 66 1.09 66 1.11 Product distribution: Alt-A 2 4.95 3 5.00 Vintages: 2004 and prior 4 3.28 5 2.82 2005-2008 6 6.55 8 6.39 2009-2017 90 0.53 87 0.36 __________ (1) Consists of the portion of our single-family conventional guaranty book of business for which we have detailed loan level information, which constituted approximately 99% of our total single-family conventional guaranty book of business as of December 31, 2017 and 2016 . (2) Consists of single-family conventional loans that were 90 days or more past due or in the foreclosure process as of December 31, 2017 and 2016 . (3) Calculated based on the aggregate unpaid principal balance of single-family conventional loans for each category divided by the aggregate unpaid principal balance of loans in our single-family conventional guaranty book of business. (4) Calculated based on the number of single-family conventional loans that were delinquent divided by the total number of loans in our single-family conventional guaranty book of business.
Multifamily [Member]
Concentration Risk [Line Items]
Schedule of Delinquency Status Guaranty Book of Business [Table Text Block]	As of December 31, 2017 (1)(2) 2016 (1)(2) 30 Days Delinquent Seriously Delinquent (3) 30 Days Delinquent Seriously Delinquent (3) Percentage of multifamily guaranty book of business 0.03 % 0.11 % 0.02 % 0.05 %
Schedule of Risk Characteristics Guaranty Book of Business [Table Text Block]	As of December 31, 2017 (1) 2016 (1) Percentage of Multifamily Guaranty Book of Business (2) Percentage Seriously Delinquent (3)(4) Percentage of Multifamily Guaranty Book of Business (2) Percentage Seriously Delinquent (3)(4) Original LTV ratio: Greater than 80% 2 % 0.21 % 2 % 0.22 % Less than or equal to 80% 98 0.11 98 0.05 Current DSCR less than 1.0 (5) 2 1.96 2 1.96 __________ (1) Consists of the portion of our multifamily guaranty book of business for which we have detailed loan level information, which constituted approximately 99% of our total multifamily guaranty book of business as of December 31, 2017 and 2016 , excluding loans that have been defeased. (2) Calculated based on the aggregate unpaid principal balance of multifamily loans for each category divided by the aggregate unpaid principal balance of loans in our multifamily guaranty book of business. (3) Consists of multifamily loans that were 60 days or more past due as of the dates indicated. (4) Calculated based on the unpaid principal balance of multifamily loans that were seriously delinquent divided by the aggregate unpaid principal balance of multifamily loans for each category included in our guaranty book of business. (5) Our estimates of current DSCRs are based on the latest available income information for these properties. Although we use the most recently available results of our multifamily borrowers, there is a lag in reporting, which typically can range from 3 to 6 months but in some cases may be longer.

Netting Arrangements (Tables)

Netting Arrangements (Tables)	12 Months Ended
	Dec. 31, 2017
Offsetting [Abstract]
Offsetting [Table Text Block]	The tables below display information related to derivatives, securities purchased under agreements to resell or similar arrangements, and securities sold under agreements to repurchase or similar arrangements, which are subject to an enforceable master netting arrangement or similar agreement that are either offset or not offset in our consolidated balance sheets. As of December 31, 2017 Gross Amount Offset (1) Net Amount Presented in our Consolidated Balance Sheets Amounts Not Offset in our Consolidated Balance Sheets Gross Amount Financial Instruments (2) Collateral (3) Net Amount (Dollars in millions) Assets: OTC risk management derivatives $ 2,479 $ (2,464 ) $ 15 $ — $ — $ 15 Cleared risk management derivatives 1,811 (1,808 ) 3 — — 3 Mortgage commitment derivatives 132 — 132 (117 ) (1 ) 14 Total derivative assets 4,422 (4,272 ) 150 (4 ) (117 ) (1 ) 32 Securities purchased under agreements to resell or similar arrangements (5) 44,670 — 44,670 — (44,670 ) — Total assets $ 49,092 $ (4,272 ) $ 44,820 $ (117 ) $ (44,671 ) $ 32 Liabilities: OTC risk management derivatives $ (3,045 ) $ 2,957 $ (88 ) $ — $ — $ (88 ) Cleared risk management derivatives (2,033 ) 2,022 (11 ) — 11 — Mortgage commitment derivatives (228 ) — (228 ) 117 93 (18 ) Total derivative liabilities (5,306 ) 4,979 (327 ) (4 ) 117 104 (106 ) Total liabilities $ (5,306 ) $ 4,979 $ (327 ) $ 117 $ 104 $ (106 ) As of December 31, 2016 Gross Amount Offset (1) Net Amount Presented in our Consolidated Balance Sheets Amounts Not Offset in our Consolidated Balance Sheets Gross Amount Financial Instruments (2) Collateral (3) Net Amount (Dollars in millions) Assets: OTC risk management derivatives $ 3,688 $ (3,667 ) $ 21 $ — $ — $ 21 Cleared risk management derivatives 849 (847 ) 2 — — 2 Mortgage commitment derivatives 631 — 631 (357 ) (22 ) 252 Total derivative assets 5,168 (4,514 ) 654 (4 ) (357 ) (22 ) 275 Securities purchased under agreements to resell or similar arrangements (5) 51,115 — 51,115 — (51,115 ) — Total assets $ 56,283 $ (4,514 ) $ 51,769 $ (357 ) $ (51,137 ) $ 275 Liabilities: OTC risk management derivatives $ (4,905 ) $ 4,520 $ (385 ) $ — $ — $ (385 ) Cleared risk management derivatives (2,415 ) 2,324 (91 ) — 91 — Mortgage commitment derivatives (737 ) — (737 ) 357 16 (364 ) Total derivative liabilities (8,057 ) 6,844 (1,213 ) (4 ) 357 107 (749 ) Total liabilities $ (8,057 ) $ 6,844 $ (1,213 ) $ 357 $ 107 $ (749 ) ________ (1) Represents the effect of the right to offset under legally enforceable master netting arrangements to settle with the same counterparty on a net basis, including cash collateral posted and received and accrued interest. (2) Mortgage commitment derivative amounts reflect where we have recognized both an asset and a liability with the same counterparty under an enforceable master netting arrangement but we have not elected to offset the related amounts in our consolidated balance sheets. (3) Represents collateral received that has not been recognized and not offset in our consolidated balance sheets as well as collateral posted which has been recognized but not offset in our consolidated balance sheets. Does not include collateral held or posted in excess of our exposure. The fair value of non-cash collateral we pledged was $747 million and $1.3 billion as of December 31, 2017 and December 31, 2016 , respectively, which the counterparty was permitted to sell or repledge. The fair value of non-cash collateral received was $44.7 billion and $51.2 billion , of which $42.5 billion and $45.5 billion could be sold or repledged as of December 31, 2017 and December 31, 2016 , respectively. None of the underlying collateral was sold or repledged as of December 31, 2017 and December 31, 2016 . (4) Excludes derivative assets of $21 million and $33 million as of December 31, 2017 and 2016 , respectively, and derivative liabilities of $1 million and $2 million recognized in our consolidated balance sheets as of December 31, 2017 and 2016 , respectively, that are not subject to enforceable master netting arrangements. (5) Includes $25.2 billion and $20.7 billion of securities purchased under agreements to resell classified as “Cash and cash equivalents” in our consolidated balance sheets as of December 31, 2017 and 2016 , respectively.

Fair Value (Tables)

Fair Value (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Recurring Changes in Fair Value [Table Text Block]	The following tables display our assets and liabilities measured in our consolidated balance sheets at fair value on a recurring basis subsequent to initial recognition, including instruments for which we have elected the fair value option. Fair Value Measurements as of December 31, 2017 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Netting Adjustment (1) Estimated Fair Value (Dollars in millions) Recurring fair value measurements: Assets: Trading securities: Mortgage-related securities: Fannie Mae $ — $ 2,905 $ 971 $ — $ 3,876 Other agency — 1,083 35 — 1,118 Alt-A and subprime private-label securities — 259 194 — 453 CMBS — 9 — — 9 Mortgage revenue bonds — — 1 — 1 Non-mortgage-related securities: U.S. Treasury securities 29,222 — — — 29,222 Total trading securities 29,222 4,256 1,201 — 34,679 Available-for-sale securities: Mortgage-related securities: Fannie Mae — 1,911 208 — 2,119 Other agency — 357 — — 357 Alt-A and subprime private-label securities — 1,237 77 — 1,314 CMBS — 15 — — 15 Mortgage revenue bonds — — 671 — 671 Other — 10 357 — 367 Total available-for-sale securities — 3,530 1,313 — 4,843 Mortgage loans — 9,480 1,116 — 10,596 Other assets: Risk management derivatives: Swaps — 4,035 146 — 4,181 Swaptions — 108 — — 108 Other — — 22 — 22 Netting adjustment — — — (4,272 ) (4,272 ) Mortgage commitment derivatives — 131 1 — 132 Total other assets — 4,274 169 (4,272 ) 171 Total assets at fair value $ 29,222 $ 21,540 $ 3,799 $ (4,272 ) $ 50,289 Fair Value Measurements as of December 31, 2017 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Netting Adjustment (1) Estimated Fair Value (Dollars in millions) Liabilities: Long-term debt: Of Fannie Mae: Senior floating $ — $ 7,810 $ 376 $ — $ 8,186 Total of Fannie Mae — 7,810 376 — 8,186 Of consolidated trusts — 29,911 582 — 30,493 Total long-term debt — 37,721 958 — 38,679 Other liabilities: Risk management derivatives: Swaps — 4,721 33 — 4,754 Swaptions — 324 — — 324 Other — — 1 — 1 Netting adjustment — — — (4,979 ) (4,979 ) Mortgage commitment derivatives — 227 1 — 228 Total other liabilities — 5,272 35 (4,979 ) 328 Total liabilities at fair value $ — $ 42,993 $ 993 $ (4,979 ) $ 39,007 Fair Value Measurements as of December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Netting Adjustment (1) Estimated Fair Value (Dollars in millions) Assets: Trading securities: Mortgage-related securities: Fannie Mae $ — $ 3,934 $ 835 $ — $ 4,769 Other agency — 2,058 — — 2,058 Alt-A and subprime private-label securities — 365 271 — 636 CMBS — 761 — — 761 Mortgage revenue bonds — — 21 — 21 Non-mortgage-related securities: U.S. Treasury securities 32,317 — — — 32,317 Total trading securities 32,317 7,118 1,127 — 40,562 Available-for-sale securities: Mortgage-related securities: Fannie Mae — 2,324 230 — 2,554 Other agency — 542 5 — 547 Alt-A and subprime private-label securities — 2,492 217 — 2,709 CMBS — 819 — — 819 Mortgage revenue bonds — — 1,272 — 1,272 Other — 33 429 — 462 Total available-for-sale securities — 6,210 2,153 — 8,363 Mortgage loans — 10,860 1,197 — 12,057 Other assets: Risk management derivatives: Swaps — 4,159 137 — 4,296 Swaptions — 241 — — 241 Other — — 33 — 33 Netting adjustment — — — (4,514 ) (4,514 ) Mortgage commitment derivatives — 619 12 — 631 Total other assets — 5,019 182 (4,514 ) 687 Total assets at fair value $ 32,317 $ 29,207 $ 4,659 $ (4,514 ) $ 61,669 Fair Value Measurements as of December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Netting Adjustment (1) Estimated Fair Value (Dollars in millions) Liabilities: Long-term debt: Of Fannie Mae: Senior floating $ — $ 9,235 $ 347 $ — $ 9,582 Total of Fannie Mae — 9,235 347 — 9,582 Of consolidated trusts — 36,283 241 — 36,524 Total long-term debt — 45,518 588 — 46,106 Other liabilities: Risk management derivatives: Swaps — 6,933 48 — 6,981 Swaptions — 339 — — 339 Other — — 2 — 2 Netting adjustment — — — (6,844 ) (6,844 ) Mortgage commitment derivatives — 649 88 — 737 Total other liabilities — 7,921 138 (6,844 ) 1,215 Total liabilities at fair value $ — $ 53,439 $ 726 $ (6,844 ) $ 47,321 __________ (1) Derivative contracts are reported on a gross basis by level. The netting adjustment represents the effect of the legal right to offset under legally enforceable master netting arrangements to settle with the same counterparty on a net basis, including cash collateral posted and received.
Fair Value Measurements Using Significant Unobservable Inputs (Level 3) [Table Text Block]	The following tables display a reconciliation of all assets and liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3). The tables also display gains and losses due to changes in fair value, including both realized and unrealized gains and losses, recognized in our consolidated statements of operations and comprehensive income for Level 3 assets and liabilities. When assets and liabilities are transferred between levels, we recognize the transfer as of the end of the period. Fair Value Measurements Using Significant Unobservable Inputs (Level 3) For the Year Ended December 31, 2017 Total Gains (Losses) (Realized/Unrealized) Net Unrealized Gains (Losses) Included in Net Income Related to Assets and Liabilities Still Held as of December 31, 2017 (5)(6) Balance, December 31, 2016 Included in Net Income Included in Total Other Comprehensive Income (Loss) (1) Purchases (2) Sales (2) Issues (3) Settlements (3) Transfers out of Level 3 (4) Transfers into Level 3 (4) Balance, December 31, 2017 (Dollars in millions) Trading securities: Mortgage-related: Fannie Mae $ 835 $ 41 $ — $ 64 $ — $ — $ (5 ) $ (991 ) $ 1,027 $ 971 $ 6 Other agency — — — 35 — — — — — 35 — Alt-A and subprime private-label securities 271 15 — — (60 ) — (32 ) — — 194 5 Mortgage revenue bonds 21 3 — — (21 ) — (2 ) — — 1 — Total trading securities $ 1,127 $ 59 (6)(7) $ — $ 99 $ (81 ) $ — $ (39 ) $ (991 ) $ 1,027 $ 1,201 $ 11 Available-for-sale securities: Mortgage-related: Fannie Mae $ 230 $ 2 $ (1 ) $ — $ — $ — $ (9 ) $ (72 ) $ 58 $ 208 $ — Other agency 5 — — — (1 ) — — (4 ) — — — Alt-A and subprime private-label securities 217 54 (53 ) — (105 ) — (36 ) — — 77 — Mortgage revenue bonds 1,272 35 (11 ) — (392 ) — (233 ) — — 671 — Other 429 8 (11 ) — (5 ) — (64 ) — — 357 — Total available-for-sale securities $ 2,153 $ 99 (7)(8) $ (76 ) $ — $ (503 ) $ — $ (342 ) $ (76 ) $ 58 $ 1,313 $ — Mortgage loans $ 1,197 $ 45 (6)(7) $ — $ 5 $ — $ — $ (233 ) $ (70 ) $ 172 $ 1,116 $ 25 Net derivatives 44 111 (6) — — — — (22 ) 6 (5 ) 134 13 Long-term debt: Of Fannie Mae: Senior floating $ (347 ) $ (29 ) (6) $ — $ — $ — $ — $ — $ — $ — $ (376 ) $ (29 ) Of consolidated trusts (241 ) (9 ) (6)(7) — — — (2 ) 66 388 (784 ) (582 ) (11 ) Total long-term debt $ (588 ) $ (38 ) $ — $ — $ — $ (2 ) $ 66 $ 388 $ (784 ) $ (958 ) $ (40 ) Fair Value Measurements Using Significant Unobservable Inputs (Level 3) For the Year Ended December 31, 2016 Total Gains (Losses) (Realized/Unrealized) Net Unrealized Gains (Losses) Included in Net Income Related to Assets and Liabilities Still Held as of December 31, 2016 (5)(6) Balance, December 31, 2015 Included in Net Income Included in Total Other Comprehensive Income (Loss) (1) Purchases (2) Sales (2) Issues (3) Settlements (3) Transfers out of Level 3 (4) Transfers into Level 3 (4) Balance, December 31, 2016 (Dollars in millions) Trading securities: Mortgage-related: Fannie Mae $ — $ — $ — $ — $ — $ — $ (1 ) $ (24 ) $ 860 $ 835 $ — Other agency — — — — — — — (1 ) 1 — — Alt-A and subprime private-label securities 949 (33 ) — — (231 ) — (51 ) (363 ) — 271 (1 ) Mortgage revenue bonds 449 33 — — (448 ) — (13 ) — — 21 (2 ) Total trading securities $ 1,398 $ — (6)(7) $ — $ — $ (679 ) $ — $ (65 ) $ (388 ) $ 861 $ 1,127 $ (3 ) Available-for-sale securities: Mortgage-related: Fannie Mae $ — $ — $ — $ — $ — $ — $ — $ (1 ) $ 231 $ 230 $ — Other agency 4 — — — — — — (4 ) 5 5 — Alt-A and subprime private-label securities 4,322 184 (233 ) — (997 ) — (220 ) (2,839 ) — 217 — Mortgage revenue bonds 2,701 132 (34 ) — (1,129 ) — (398 ) — — 1,272 — Other 1,404 — (12 ) — (605 ) — (74 ) (284 ) — 429 — Total available-for-sale securities $ 8,431 $ 316 (7)(8) $ (279 ) $ — $ (2,731 ) $ — $ (692 ) $ (3,128 ) $ 236 $ 2,153 $ — Mortgage loans $ 1,477 $ 129 (6)(7) $ — $ 36 $ (392 ) $ — $ (255 ) $ (77 ) $ 279 $ 1,197 $ 17 Net derivatives 157 15 (6) — — — (8 ) (122 ) 2 — 44 (132 ) Long-term debt: Of Fannie Mae: Senior floating $ (369 ) $ 22 (6) $ — $ — $ — $ — $ — $ — $ — $ (347 ) $ 22 Of consolidated trusts (496 ) (75 ) (6)(7) — — — (74 ) 378 215 (189 ) (241 ) (9 ) Total long-term debt $ (865 ) $ (53 ) $ — $ — $ — $ (74 ) $ 378 $ 215 $ (189 ) $ (588 ) $ 13 Fair Value Measurements Using Significant Unobservable Inputs (Level 3) For the Year Ended December 31, 2015 Total Gains (Losses) (Realized/Unrealized) Net Unrealized Gains (Losses) Included in Net Income Related to Assets and Liabilities Still Held as of December 31, 2015 (5)(6) Balance, December 31, 2014 Included in Net Income Included in Total Other Comprehensive Income (Loss) (1) Purchases (2) Sales (2) Issues (3) Settlements (3) Transfers out of Level 3 (4) Transfers into Level 3 (4) Balance, December 31, 2015 (Dollars in millions) Trading securities: Mortgage-related: Fannie Mae $ 305 $ (27 ) $ — $ — $ (2 ) $ — $ — $ (278 ) $ 2 $ — $ — Alt-A and subprime private-label securities 1,904 72 — — (878 ) — (133 ) (44 ) 28 949 25 Mortgage revenue bonds 722 (41 ) — — (220 ) — (12 ) — — 449 (33 ) Other 99 4 — — (100 ) — (3 ) — — — — Total trading securities $ 3,030 $ 8 (6)(7) $ — $ — $ (1,200 ) $ — $ (148 ) $ (322 ) $ 30 $ 1,398 $ (8 ) Available-for-sale securities: Mortgage-related: Fannie Mae $ — $ — $ — $ 421 $ (425 ) $ — $ (8 ) $ — $ 12 $ — $ — Other agency 6 — — — — — (1 ) (2 ) 1 4 — Alt-A and subprime private-label securities 8,380 814 (555 ) — (3,079 ) — (1,037 ) (538 ) 337 4,322 — Mortgage revenue bonds 4,023 51 (104 ) — (410 ) — (859 ) — — 2,701 — Other 2,671 (26 ) (2 ) — (1,012 ) — (227 ) — — 1,404 — Total available-for-sale securities $ 15,080 $ 839 (7)(8) $ (661 ) $ 421 $ (4,926 ) $ — $ (2,132 ) $ (540 ) $ 350 $ 8,431 $ — Mortgage loans $ 1,833 $ 57 (6)(7) $ — $ 5 $ — $ — $ (350 ) $ (377 ) $ 309 $ 1,477 $ (20 ) Net derivatives 45 (55 ) (6) — — — (4 ) 169 (7 ) 9 157 (2 ) Long-term debt: Of Fannie Mae: Senior floating $ (363 ) $ (6 ) (6) $ — $ — $ — $ — $ — $ — $ — $ (369 ) $ (6 ) Of consolidated trusts (527 ) (9 ) (6)(7) — — — (66 ) 57 228 (179 ) (496 ) 17 Total long-term debt $ (890 ) $ (15 ) $ — $ — $ — $ (66 ) $ 57 $ 228 $ (179 ) $ (865 ) $ 11 __________ (1) Losses included in other comprehensive income are included in “Changes in unrealized gains on available-for-sale securities, net of reclassification adjustments and taxes” in our consolidated statements of operations and comprehensive income. (2) Purchases and sales include activity related to the consolidation and deconsolidation of assets of securitization trusts. (3) Issues and settlements include activity related to the consolidation and deconsolidation of liabilities of securitization trusts. (4) Transfers into and out of Level 3 consisted primarily of Fannie Mae securities backed by private-label mortgage-related securities. Prices for these securities are based on inputs that were not readily observable. Transfers out of Level 3 also occurred for private-label mortgage-related securities backed by Alt-A loans and subprime loans. Prices for these securities were available from multiple third-party vendors and demonstrated an increased and sustained level of observability over time. (5) Amount represents temporary changes in fair value. Amortization, accretion and OTTI are not considered unrealized and are not included in this amount. (6) Gains (losses) are included in “Fair value losses, net” in our consolidated statements of operations and comprehensive income. (7) Gains (losses) are included in “Net interest income” in our consolidated statements of operations and comprehensive income. (8) Gains (losses) are included in “Investment gains, net” in our consolidated statements of operations and comprehensive income.
Valuation Techniques and Significant Unobservable Inputs for Level 3 Assets and Liabilities [Table Text Block]	The following tables display valuation techniques and the range and the weighted average of significant unobservable inputs for our Level 3 assets and liabilities measured at fair value on a recurring basis. Fair Value Measurements as of December 31, 2017 Fair Value Significant Valuation Techniques Significant Unobservable Inputs (1) Range (1) Weighted - Average (1) (Dollars in millions) Recurring fair value measurements: Trading securities: Mortgage-related securities: Agency (2) $ 971 Single Vendor Prepayment Speed (%) 0.0 - 177.0 160.0 Spreads (bps) 51.5 - 375.0 200.1 35 Various Total agency 1,006 Alt-A and subprime private-label securities 154 Consensus 40 Various Total Alt-A and subprime private-label securities 194 Mortgage revenue bonds 1 Various Total trading securities $ 1,201 Fair Value Measurements as of December 31, 2017 Fair Value Significant Valuation Techniques Significant Unobservable Inputs (1) Range (1) Weighted - Average (1) (Dollars in millions) Available-for-sale securities: Mortgage-related securities: Agency (2) $ 112 Single Vendor Prepayment Speed (%) 0.0 - 175.7 147.1 Spreads (bps) 150.0 - 210.0 182.3 96 Various Total agency 208 Alt-A and subprime private-label securities 77 Various Mortgage revenue bonds 475 Single Vendor Spreads (bps) (17.0 ) - 248.0 39.0 196 Various Total mortgage revenue bonds 671 Other 325 Discounted Cash Flow Prepayment Speed (%) 1.6 - 2.5 2.5 Severity (%) 50.0 - 88.0 86.6 Spreads (bps) 84.8 - 607.0 577.9 32 Various Total other 357 Total available-for-sale securities $ 1,313 Mortgage loans: Single-family $ 406 Build-Up 344 Consensus 208 Various Total single-family 958 Multifamily 155 Build-Up Spreads (bps) 29.0 - 267.2 105.8 3 Various Total multifamily $ 158 Total mortgage loans $ 1,116 Net derivatives $ 113 Dealer Mark 21 Various Total net derivatives $ 134 Long-term debt: Of Fannie Mae: Senior floating $ (376 ) Discounted Cash Flow Of consolidated trusts (3) (401 ) Discounted Cash Flow Default Rate (%) 1.6 - 6.3 4.6 Prepayment Speed (%) 5.4 - 100.0 98.9 Severity (%) 28.0 - 95.0 71.5 Spreads (bps) 42.0 - 228.3 78.7 (181 ) Various Total of consolidated trusts (582 ) Total long-term debt $ (958 ) Fair Value Measurements as of December 31, 2016 Fair Value Significant Valuation Techniques Significant Unobservable Inputs (1) Range (1) Weighted - Average (1) (Dollars in millions) Recurring fair value measurements: Trading securities: Mortgage-related securities: Agency (2) $ 809 Consensus 26 Various Total agency 835 Alt-A and subprime private-label securities 232 Consensus Default Rate (%) 0.4 - 10.9 8.2 Prepayment Speed (%) 4.3 - 7.4 6.6 Severity (%) 71.0 - 95.0 88.9 Spreads (bps) 244.6 - 253.9 251.5 39 Consensus Total Alt-A and subprime private-label securities 271 Mortgage revenue bonds 19 Discounted Cash Flow Spreads (bps) 13.0 - 268.2 252.2 2 Various Total mortgage revenue bonds 21 Total trading securities $ 1,127 Available-for-sale securities: Mortgage-related securities: Agency (2) $ 129 Single Vendor Prepayment Speed (%) 124.8 - 165.5 142.4 Spreads (bps) 175.0 - 210.0 182.5 72 Consensus 34 Various Total agency 235 Alt-A and subprime private-label securities 93 Single Vendor Default Rate (%) 2.5 - 8.0 3.8 Prepayment Speed (%) 3.0 - 11.0 4.9 Severity (%) 38.0 - 80.0 48.1 Spreads (bps) 266.1 - 306.8 297.1 45 Discounted Cash Flow Spreads (bps) 361.0 - 450.0 406.0 79 Various Total Alt-A and subprime private-label securities 217 Mortgage revenue bonds 684 Single Vendor Spreads (bps) (16.8 ) - 336.9 44.3 126 Single Vendor 435 Discounted Cash Flow Spreads (bps) (16.8 ) - 391.1 260.0 27 Various Total mortgage revenue bonds 1,272 Other 47 Consensus Default Rate (%) 0.5 - 3.5 3.5 Prepayment Speed (%) 2.5 - 6.0 2.5 Severity (%) 20.0 - 88.0 87.5 Spreads (bps) 221.6 - 300.2 237.7 348 Discounted Cash Flow Default Rate (%) 2.3 2.3 Prepayment Speed (%) 0.5 0.5 Severity (%) 95.0 95.0 Spreads (bps) 190.0 - 450.0 449.1 34 Various Total other 429 Total available-for-sale securities $ 2,153 Fair Value Measurements as of December 31, 2016 Fair Value Significant Valuation Techniques Significant Unobservable Inputs (1) Range (1) Weighted - Average (1) (Dollars in millions) Mortgage loans: Single-family $ 516 Build-Up 300 Consensus 218 Various Total single-family 1,034 Multifamily 163 Build-Up Spreads (bps) 55.0 - 305.2 140.2 Total mortgage loans $ 1,197 Net derivatives $ 10 Internal Model 89 Dealer Mark 21 Discounted Cash Flow (76 ) Various Total net derivatives $ 44 Long-term debt: Of Fannie Mae: Senior floating $ (347 ) Discounted Cash Flow Of consolidated trusts (241 ) Various Total long-term debt $ (588 ) _________ (1) Valuation techniques for which no unobservable inputs are disclosed generally reflect the use of third-party pricing services or dealers, and the range of unobservable inputs applied by these sources is not readily available or cannot be reasonably estimated. Where we have disclosed unobservable inputs for consensus and single vendor techniques, those inputs are based on our validations performed at the security level using discounted cash flows. The prepayment speed used for available-for-sale agency securities is the Public Securities Association (“PSA”) prepayment speed, which can be greater than 100%. For all other securities, the Conditional Prepayment Rate (“CPR”) is used as the prepayment speed, which can be between 0% and 100%. (2) Includes Fannie Mae and Freddie Mac securities. (3) Includes instruments for which the prepayment speed represents the estimated annualized rate of prepayment after all prepayment penalty provisions have expired and also instruments for which prepayment speed represents the estimated rate of prepayment over the remaining life of the instrument.
Level 3 Assets Measured on Nonrecurring Basis [Table Text Block]	The following table displays valuation techniques for our Level 3 assets measured at fair value on a nonrecurring basis. The significant unobservable inputs related to these techniques primarily relate to collateral dependent valuations. The related ranges and weighted averages are not meaningful when aggregated as they vary significantly from property to property. Fair Value Measurements as of December 31, Valuation Techniques 2017 2016 (Dollars in millions) Nonrecurring fair value measurements: Mortgage loans held for sale, at lower of cost or fair value Consensus $ 1,113 $ 1,025 Single Vendor 1,880 54 Various — 9 Total mortgage loans held for sale, at lower of cost or fair value 2,993 1,088 Single-family mortgage loans held for investment, at amortized cost Internal Model 1,623 2,816 Multifamily mortgage loans held for investment, at amortized cost Broker Price Opinions 28 25 Asset Manager Estimate 163 170 Various 4 3 Total multifamily mortgage loans held for investment, at amortized cost 195 198 Acquired property, net: (1) Single-family Accepted Offers 218 340 Appraisals 438 571 Walk Forwards 222 306 Internal Model 319 476 Various 113 99 Total single-family 1,310 1,792 Multifamily Various 19 — Other assets Various 2 12 Total nonrecurring assets at fair value $ 6,142 $ 5,906 _________ (1) The most commonly used techniques in our valuation of acquired property are proprietary home price model and third-party valuations (both current and walk forward). Based on the number of properties measured as of December 31, 2017 , these methodologies comprised approximately 77% of our valuations, while accepted offers comprised approximately 18% of our valuations. Based on the number of properties measured as of December 31, 2016 , these methodologies comprised approximately 75% of our valuations, while accepted offers comprised approximately 19% of our valuations.
Fair Value of Financial Instruments [Table Text Block]	The following table displays the carrying value and estimated fair value of our financial instruments. The fair value of financial instruments we disclose includes commitments to purchase multifamily and single-family mortgage loans that we do not record in our consolidated balance sheets. The fair values of these commitments are included as “Mortgage loans held for investment, net of allowance for loan losses.” The disclosure excludes all non-financial instruments; therefore, the fair value of our financial assets and liabilities does not represent the underlying fair value of our total consolidated assets and liabilities. As of December 31, 2017 Carrying Quoted Price in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Netting Adjustment Estimated (Dollars in millions) Financial assets: Cash and cash equivalents and restricted cash $ 60,260 $ 35,060 $ 25,200 $ — $ — $ 60,260 Federal funds sold and securities purchased under agreements to resell or similar arrangements 19,470 — 19,470 — — 19,470 Trading securities 34,679 29,222 4,256 1,201 — 34,679 Available-for-sale securities 4,843 — 3,530 1,313 — 4,843 Mortgage loans held for sale 4,988 — 101 5,333 — 5,434 Mortgage loans held for investment, net of allowance for loan losses 3,173,537 — 2,886,470 315,719 — 3,202,189 Advances to lenders 4,938 — 4,936 2 — 4,938 Derivative assets at fair value 171 — 4,274 169 (4,272 ) 171 Guaranty assets and buy-ups 149 — — 436 — 436 Total financial assets $ 3,303,035 $ 64,282 $ 2,948,237 $ 324,173 $ (4,272 ) $ 3,332,420 Financial liabilities: Short-term debt: Of Fannie Mae $ 33,377 $ — $ 33,379 $ — $ — $ 33,379 Of consolidated trusts 379 — — 378 — 378 Long-term debt: Of Fannie Mae 243,375 — 249,780 837 — 250,617 Of consolidated trusts 3,052,923 — 3,014,250 40,683 — 3,054,933 Derivative liabilities at fair value 328 — 5,272 35 (4,979 ) 328 Guaranty obligations 258 — — 456 — 456 Total financial liabilities $ 3,330,640 $ — $ 3,302,681 $ 42,389 $ (4,979 ) $ 3,340,091 As of December 31, 2016 Carrying Quoted Price in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Netting Adjustment Estimated (Dollars in millions) Financial assets: Cash and cash equivalents and restricted cash $ 62,177 $ 41,477 $ 20,700 $ — $ — $ 62,177 Federal funds sold and securities purchased under agreements to resell or similar arrangements 30,415 — 30,415 — — 30,415 Trading securities 40,562 32,317 7,118 1,127 — 40,562 Available-for-sale securities 8,363 — 6,210 2,153 — 8,363 Mortgage loans held for sale 2,899 — 509 2,751 — 3,260 Mortgage loans held for investment, net of allowance for loan losses 3,076,854 — 2,767,813 316,742 — 3,084,555 Advances to lenders 7,494 — 7,156 352 — 7,508 Derivative assets at fair value 687 — 5,019 182 (4,514 ) 687 Guaranty assets and buy-ups 158 — — 432 — 432 Total financial assets $ 3,229,609 $ 73,794 $ 2,844,940 $ 323,739 $ (4,514 ) $ 3,237,959 Financial liabilities: Short-term debt: Of Fannie Mae $ 34,995 $ — $ 34,998 $ — $ — $ 34,998 Of consolidated trusts 584 — — 584 — 584 Long-term debt: Of Fannie Mae 292,102 — 298,980 770 — 299,750 Of consolidated trusts 2,934,635 — 2,901,316 36,668 — 2,937,984 Derivative liabilities at fair value 1,215 — 7,921 138 (6,844 ) 1,215 Guaranty obligations 280 — — 710 — 710 Total financial liabilities $ 3,263,811 $ — $ 3,243,215 $ 38,870 $ (6,844 ) $ 3,275,241
Fair Value Option [Table Text Block]	The following table displays the fair value and unpaid principal balance of the financial instruments for which we have made fair value elections. As of December 31, 2017 2016 Loans (1) Long-Term Debt of Fannie Mae Long-Term Debt of Consolidated Trusts Loans (1) Long-Term Debt of Fannie Mae Long-Term Debt of Consolidated Trusts (Dollars in millions) Fair value $ 10,596 $ 8,186 $ 30,493 $ 12,057 $ 9,582 $ 36,524 Unpaid principal balance 10,246 7,368 27,717 11,688 9,090 33,055 __________ (1) Includes nonaccrual loans with a fair value of $227 million and $200 million as of December 31, 2017 and 2016 , respectively. The difference between unpaid principal balance and the fair value of these nonaccrual loans as of December 31, 2017 and 2016 is $46 million and $34 million , respectively. Includes loans that are 90 days or more past due with a fair value of $159 million and $152 million as of December 31, 2017 and 2016 , respectively. The difference between unpaid principal balance and the fair value of these 90 or more days past due loans as of December 31, 2017 and 2016 is $34 million and $25 million , respectively. The following table displays fair value gains and losses, net, including changes attributable to instrument-specific credit risk, for loans and debt for which the fair value election was made. Amounts are recorded as a component of “Fair value losses, net” in our consolidated statements of operations and comprehensive income. For the Year Ended December 31, 2017 2016 2015 Loans Long-Term Debt Total Gains (Losses) Loans Long-Term Debt Total Gains (Losses) Loans Long-Term Debt Total Gains (Losses) (Dollars in millions) Changes in instrument-specific credit risk $ 67 $ (316 ) $ (249 ) $ 23 $ (648 ) $ (625 ) $ 86 $ 39 $ 125 Other changes in fair value 69 22 91 72 193 265 (191 ) 146 (45 ) Fair value gains (losses), net $ 136 $ (294 ) $ (158 ) $ 95 $ (455 ) $ (360 ) $ (105 ) $ 185 $ 80

Commitments and Contingencies51

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Non Cancelable Future Commitments by Remaining Maturity [Table Text Block]	The following table summarizes by remaining maturity, non-cancelable future commitments related to loan and mortgage purchases, operating leases and other agreements. As of December 31, 2017 Loans and Mortgage-Related Securities (1) Operating Leases (2) Other (3) (Dollars in millions) 2018 $ 73,130 $ 41 $ 98 2019 — 48 57 2020 — 56 73 2021 — 56 14 2022 — 58 1 Thereafter — 609 — Total $ 73,130 $ 868 $ 243 __________ (1) Primarily includes $72.7 billion that has been accounted for as mortgage commitment derivatives. (2) Includes amounts related to office buildings and equipment leases. (3) Includes purchase commitments for certain telecommunications services, computer software and services, and other agreements and commitments.

Selected Quarterly Financial 52

Selected Quarterly Financial Information (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of Selected Quarterly Financial Information [Table Text Block]	The consolidated statements of operations for the quarterly periods in 2017 and 2016 are unaudited and in the opinion of management include all adjustments, consisting of normal recurring adjustments, necessary for a fair presentation of our consolidated statements of operations. Certain prior period amounts have been reclassified to conform to the current period presentation. The operating results for the interim periods are not necessarily indicative of the operating results to be expected for a full year or for other interim periods. For the 2017 Quarter Ended March 31 June 30 September 30 December 31 (Dollars and shares in millions, except per share amounts) Interest income: Trading securities $ 142 $ 176 $ 195 $ 193 Available-for-sale securities 101 91 77 66 Mortgage loans 27,047 27,011 27,047 27,214 Other 94 115 142 145 Total interest income 27,384 27,393 27,461 27,618 Interest expense: Short-term debt (44 ) (57 ) (72 ) (77 ) Long-term debt (21,994 ) (22,334 ) (22,115 ) (22,430 ) Total interest expense (22,038 ) (22,391 ) (22,187 ) (22,507 ) Net interest income 5,346 5,002 5,274 5,111 Benefit (provision) for credit losses 396 1,267 (182 ) 560 Net interest income after benefit (provision) for credit losses 5,742 6,269 5,092 5,671 Investment gains (losses), net (9 ) 385 313 833 Fair value gains (losses), net (40 ) (691 ) (289 ) (191 ) Fee and other income 249 353 1,194 431 Non-interest income 200 47 1,218 1,073 Administrative expenses: Salaries and employee benefits (344 ) (332 ) (331 ) (321 ) Professional services (229 ) (234 ) (218 ) (252 ) Other administrative expenses (111 ) (120 ) (115 ) (130 ) Total administrative expenses (684 ) (686 ) (664 ) (703 ) Foreclosed property expense (217 ) (34 ) (140 ) (130 ) TCCA fees (503 ) (518 ) (531 ) (544 ) Other expenses, net (382 ) (291 ) (427 ) (411 ) Total expenses (1,786 ) (1,529 ) (1,762 ) (1,788 ) Income before federal income taxes 4,156 4,787 4,548 4,956 Provision for federal income taxes (1,383 ) (1,587 ) (1,525 ) (11,489 ) Net income (loss) attributable to Fannie Mae 2,773 3,200 3,023 (6,533 ) Dividends distributed or available for distribution to senior preferred stockholder (1) (2,779 ) (3,117 ) (3,048 ) — Net income (loss) attributable to common stockholders $ (6 ) $ 83 $ (25 ) $ (6,533 ) Earnings (loss) per share: Basic $ 0.00 $ 0.01 $ 0.00 $ (1.13 ) Diluted 0.00 0.01 0.00 (1.13 ) Weighted-average common shares outstanding: Basic 5,762 5,762 5,762 5,762 Diluted 5,762 5,893 5,762 5,762 For the 2016 Quarter Ended March 31 June 30 September 30 December 31 (Dollars and shares in millions, except per share amounts) Interest income: Trading securities $ 120 $ 128 $ 140 $ 128 Available-for-sale securities 203 170 134 113 Mortgage loans 26,961 26,256 25,611 25,814 Other 48 46 66 83 Total interest income 27,332 26,600 25,951 26,138 Interest expense: Short-term debt (51 ) (57 ) (56 ) (42 ) Long-term debt (22,512 ) (21,257 ) (20,460 ) (20,291 ) Total interest expense (22,563 ) (21,314 ) (20,516 ) (20,333 ) Net interest income 4,769 5,286 5,435 5,805 Benefit (provision) for credit losses 1,184 1,601 673 (1,303 ) Net interest income after benefit (provision) for credit losses 5,953 6,887 6,108 4,502 Investment gains, net 69 398 467 322 Fair value gains (losses), net (2,813 ) (1,667 ) (491 ) 3,890 Fee and other income 203 174 175 414 Non-interest income (loss) (2,541 ) (1,095 ) 151 4,626 Administrative expenses: Salaries and employee benefits (364 ) (331 ) (322 ) (319 ) Professional services (215 ) (232 ) (237 ) (271 ) Other administrative expenses (109 ) (115 ) (102 ) (124 ) Total administrative expenses (688 ) (678 ) (661 ) (714 ) Foreclosed property expense (334 ) (63 ) (110 ) (137 ) TCCA fees (440 ) (453 ) (465 ) (487 ) Other expenses, net (264 ) (254 ) (300 ) (210 ) Total expenses (1,726 ) (1,448 ) (1,536 ) (1,548 ) Income before federal income taxes 1,686 4,344 4,723 7,580 Provision for federal income taxes (550 ) (1,398 ) (1,527 ) (2,545 ) Net income attributable to Fannie Mae 1,136 2,946 3,196 5,035 Dividends distributed or available for distribution to senior preferred stockholder (919 ) (2,869 ) (2,977 ) (5,471 ) Net income (loss) attributable to common stockholders (Note 11) $ 217 $ 77 $ 219 $ (436 ) Earnings (loss) per share: Basic $ 0.04 $ 0.01 $ 0.04 $ (0.08 ) Diluted 0.04 0.01 0.04 (0.08 ) Weighted-average common shares outstanding: Basic 5,762 5,762 5,762 5,762 Diluted 5,893 5,893 5,893 5,762 __________ (1) Subsequent to the filing of our quarterly report on Form 10-Q for the quarter ended September 30, 2017 on November 2, 2017, the dividend provisions of our senior preferred stock were amended. As a result, the amount available for distribution as of September 30, 2017 was not the amount ultimately distributed upon payment of our fourth quarter 2017 dividend. See “ Note 11, Equity (Deficit) ” for further information regarding the changes to the dividend provisions of our senior preferred stock and the dividends we paid on the senior preferred stock during 2017.

Summary of Significant Accoun53

Summary of Significant Accounting Policies Organization (Details) $ / shares in Units, $ in Millions	Dec. 29, 2017USD ($)	Sep. 08, 2008USD ($)	Dec. 31, 2017USD ($)segments	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Mar. 31, 2018USD ($)	Sep. 30, 2017USD ($)	Dec. 31, 2014USD ($)	Sep. 07, 2008$ / shares
Related Parties [Line Items]
Percentage of common shares attributable to warrants issued to Treasury as a percentage to total diluted common shares upon exercise of the right			79.90%
Net worth (deficit)			$ (3,686)	$ 6,071	$ 4,059		$ 3,600	$ 3,720
Payment Of Cash Dividends On Senior Preferred Stock To Treasury	$ 648		$ 12,015	9,624	$ 10,278
Number of Reportable Segments | segments			2
Number Of Days of Net Worth Deficit Required FHFA Must Place Us Into Receivership 1			60 days
US Treasury [Member]
Related Parties [Line Items]
Aggregate funding received from US Treasury pursuant to the senior preferred stock purchase agreement			$ 116,100	$ 116,100
Aggregate liquidation preference of senior preferred stock			120,100
Total remaining funding available from US Treasury pursuant to the senior preferred stock agreement			117,600
Common stock warrant exercise price per share | $ / shares									$ 0.00001
Fair value of the warrant at issuance		$ 3,500
Reduction in Dividends Paid			$ 2,400
Percentage of common shares attributable to warrants issued to Treasury as a percentage to total diluted common shares upon exercise of the right			79.90%						79.90%
Funding Draw Requested From U.S. Treasury Pursuant to the Senior Preferred Stock Purchase Agreement			$ 3,700
Scenario, Forecast [Member] | US Treasury [Member]
Related Parties [Line Items]
Aggregate funding received from US Treasury pursuant to the senior preferred stock purchase agreement						$ 119,800
Aggregate liquidation preference of senior preferred stock						123,800
Total remaining funding available from US Treasury pursuant to the senior preferred stock agreement						$ 113,900

Summary of Significant Accoun54

Summary of Significant Accounting Policies Related Parties (Details) - USD ($) $ / shares in Units, shares in Millions	Jan. 01, 2018	Dec. 30, 2017	Dec. 29, 2017	Sep. 08, 2008	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2018	Dec. 31, 2014	Dec. 31, 2013	Sep. 07, 2008
Related Parties [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%													35.00%	35.00%	35.00%
Convertible preferred stock									131
Weighted-average shares of common stock that would be issued upon the full exercise of the warrant issued to Treasury													4,600	4,600	4,600	4,600
Number of days after which we have not been paying debts or liabilities exceed assets FHFA must place us into receivership														60 days
Net worth (deficit)					$ (3,686,000,000)	$ 3,600,000,000			$ 6,071,000,000				$ 4,059,000,000	$ (3,686,000,000)	$ 6,071,000,000	$ 4,059,000,000		$ 3,720,000,000
Payment Of Cash Dividends On Senior Preferred Stock To Treasury			$ 648,000,000											$ 12,015,000,000	9,624,000,000	10,278,000,000
Percentage of common shares attributable to warrants issued to Treasury as a percentage to total diluted common shares upon exercise of the right					79.90%									79.90%
Income taxes paid														$ 3,090,000,000	1,711,000,000	1,170,000,000
Unpaid principal balance guaranteed by a related party					$ 4,800,000,000									4,800,000,000
Temporary Payroll Cut Continuation Act of 2011 (TCCA) fees					$ (544,000,000)	(531,000,000)	$ (518,000,000)	$ (503,000,000)	(487,000,000)	$ (465,000,000)	$ (453,000,000)	$ (440,000,000)		$ (2,096,000,000)	(1,845,000,000)	(1,621,000,000)
Basis Points of Each Dollar of Unpaid Principal Balance					420.00%									420.00%
Trading, at fair value					$ 34,679,000,000				40,562,000,000					$ 34,679,000,000	40,562,000,000
Interest Income recognized on Treasury Securities					193,000,000	195,000,000	$ 176,000,000	$ 142,000,000	128,000,000	$ 140,000,000	$ 128,000,000	$ 120,000,000		706,000,000	516,000,000	444,000,000
Accrued interest receivable					8,133,000,000				7,737,000,000					8,133,000,000	7,737,000,000
U.S. Treasury Securities [Member]
Related Parties [Line Items]
Trading, at fair value					29,222,000,000				32,317,000,000					29,222,000,000	32,317,000,000
Series 2008-2 Senior Preferred Stock [Member]
Related Parties [Line Items]
Shares of variable liquidation preference senior preferred stock issued				1
Aggregate liquidation preference of senior preferred stock				$ 1,000,000,000
Payment Of Cash Dividends On Senior Preferred Stock To Treasury		$ 648,000,000
US Treasury [Member]
Related Parties [Line Items]
Reduction in Dividends Paid					2,400,000,000									2,400,000,000
Aggregate funding received from US Treasury pursuant to the senior preferred stock purchase agreement					116,100,000,000				116,100,000,000					116,100,000,000	116,100,000,000
Aggregate liquidation preference of senior preferred stock					120,100,000,000									120,100,000,000
Total remaining funding available from US Treasury pursuant to the senior preferred stock agreement					117,600,000,000									117,600,000,000
Capital reserve amount for the fiscal year based on the amended Senior Preferred Stock Purchase agreement	$ 0				$ 600,000,000	$ 600,000,000			1,200,000,000					$ 600,000,000	1,200,000,000				$ 3,000,000,000
Percentage of common shares attributable to warrants issued to Treasury as a percentage to total diluted common shares upon exercise of the right					79.90%									79.90%						79.90%
Common stock warrant exercise price per share																				$ 0.00001
Fair value of the warrant at issuance				$ 3,500,000,000
Home Affordable Modification Program administrative expense reimbursements														$ 40,000,000	57,000,000	68,000,000
Interest Income, Related Party														$ 51,000,000	7,000,000
Income tax refund															1,500,000,000	277,000,000
Percentage of Initial Principal Loss Treasury Will Bear For the NIB Program					35.00%									35.00%
Basis Points Increase of Guarantee Fee Rate Resulting from the Temporary Payroll Tax Cut Continuation Act of 2011.					1000.00%									1000.00%
Temporary Payroll Cut Continuation Act of 2011 (TCCA) fees														$ (2,096,000,000)	(1,845,000,000)	(1,621,000,000)
Recognized TCCA fees that had not been remitted to Treasury as of period end					$ 544,000,000				487,000,000					544,000,000	487,000,000
US Treasury [Member] | Other Expense [Member]
Related Parties [Line Items]
Affordable Housing Program Assessments														84,000,000	137,000,000	111,000,000
US Treasury [Member] | U.S. Treasury Securities [Member]
Related Parties [Line Items]
Trading, at fair value					29,200,000,000				32,300,000,000					29,200,000,000	32,300,000,000
Interest Income recognized on Treasury Securities														345,000,000	157,000,000	35,000,000
Accrued interest receivable					77,000,000				39,000,000					77,000,000	39,000,000
US Treasury [Member] | Scenario, Forecast [Member]
Related Parties [Line Items]
Aggregate funding received from US Treasury pursuant to the senior preferred stock purchase agreement																	$ 119,800,000,000
Aggregate liquidation preference of senior preferred stock																	123,800,000,000
Total remaining funding available from US Treasury pursuant to the senior preferred stock agreement																	$ 113,900,000,000
Freddie Mac [Member] | Freddie Mac [Member]
Related Parties [Line Items]
Fair value of mortgage-related securities					613,000,000				1,400,000,000					613,000,000	1,400,000,000
Accrued interest receivable					$ 2,000,000				$ 5,000,000					2,000,000	5,000,000
Investment income, interest														38,000,000	112,000,000	226,000,000
Federal Housing Finance Agency [Member]
Related Parties [Line Items]
FHFA assessment fees/expense														112,000,000	114,000,000	112,000,000
Common Securitization Solutions [Member]
Related Parties [Line Items]
Payments to Acquire Equity Method Investments														$ 102,000,000	$ 118,000,000	$ 66,000,000

Summary of Significant Accoun55

Summary of Significant Accounting Policies Use of Estimates (Details) - USD ($) $ in Millions	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2015
Change in Accounting Estimate [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	35.00%	35.00%	35.00%
Fair value of guaranty obligation		$ 276	$ 446
Change in Accounting Method Accounted for as Change in Estimate [Member]
Change in Accounting Estimate [Line Items]
Advisory Bulletin impact for HFI loans					$ (1,800)
Advisory Bulletin impact for preforeclosure property taxes and insurance receivable					$ (724)

Summary of Significant Accoun56

Summary of Significant Accounting Policies Investments in Securities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Fair value of guaranty obligation	$ 276	$ 446

Summary of Significant Accoun57

Summary of Significant Accounting Policies Reserve for Guaranty Losses (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Reserve for Guaranty Losses	$ 315	$ 370

Summary of Significant Accoun58

Summary of Significant Accounting Policies Advances to Lenders (Details)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Maximum term of early lender funding advances	60 days

Summary of Significant Accoun59

Summary of Significant Accounting Policies Fee and Other Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Gain Contingencies [Line Items]
Fee and other income	$ 431	$ 1,194	$ 353	$ 249	$ 414	$ 175	$ 174	$ 203	$ 2,227	$ 966	$ 1,348
Private Label Securities Settlements [Member]
Gain Contingencies [Line Items]
Fee and other income									$ 975	$ 245	$ 21

Summary of Significant Accoun60

Summary of Significant Accounting Policies Employee Retirement Benefits (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial losses of defined pension benefit plan recorded in Administrative expenses	$ 305

Consolidations and Transfers 61

Consolidations and Transfers of Financial Assets Types of VIEs (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entities [Line Items]
Carrying value of LIHTC partnership investments	$ 0
Consolidated VIEs [Member]
Variable Interest Entities [Line Items]
Variable Interest Entity, Conclusion to Consolidate, Change in Facts and Circumstances, Amount	$ 17,000,000
Unconsolidated VIEs [Member]
Variable Interest Entities [Line Items]
Variable Interest Entity, Conclusion to Consolidate, Change in Facts and Circumstances, Amount		$ 258,000,000

Consolidations and Transfers 62

Consolidations and Transfers of Financial Assets Unconsolidated VIEs (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entities [Line Items]
Trading, at fair value	$ 34,679	$ 40,562
Available-for-sale securities	4,843	8,363
Other assets	19,049	20,942
Other liabilities	(9,479)	(10,150)
Unpaid principal balance of mortgage loans	3,155,703	3,063,646
Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	265,069	229,896
Consolidated VIEs [Member]
Variable Interest Entities [Line Items]
Available-for-sale securities	87	107
Other liabilities	(492)	(390)
Unconsolidated VIEs [Member] | Multifamily [Member]
Variable Interest Entities [Line Items]
Unpaid principal balance of mortgage loans	265,100
Unconsolidated VIEs [Member] | Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	3,809	4,642
Available-for-sale securities	2,032	2,447
Unconsolidated VIEs [Member] | Non-Fannie Mae Securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	1,580	3,473
Available-for-sale securities	2,062	4,879
Unconsolidated VIEs [Member] | Mortgage-related securities [Member]
Variable Interest Entities [Line Items]
Trading, at fair value	5,389	8,115
Available-for-sale securities	4,094	7,326
Other assets	74	77
Other liabilities	(467)	(528)
Net carrying amount	9,090	14,990
Maximum exposure to loss	15,000	21,000
Total unconsolidated assets	70,000	150,000
Unconsolidated VIEs [Member] | Partnership Interest [Member]
Variable Interest Entities [Line Items]
Net carrying amount	82	92
Maximum exposure to loss	105	118
Total unconsolidated assets	$ 3,200	$ 3,900

Consolidations and Transfers 63

Consolidations and Transfers of Financial Assets Transfers of Financial Assets (Details) - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Transfers of Financial Assets [Line Items]
Portfolio securitizations: unpaid principal balance	$ 252.7	$ 264.7	$ 212
Unconsolidated VIEs [Member]
Transfers of Financial Assets [Line Items]
Retained interests: principal and interest received	1.1	1.2	$ 1.2
Unconsolidated VIEs [Member] | Single Class MBS, REMIC & Megas [Member]
Transfers of Financial Assets [Line Items]
Retained interests: unpaid principal balance	3.9	4.4
Retained interest: fair value	$ 4.7	$ 5.8

Consolidations and Transfers 64

Consolidations and Transfers of Financial Assets Managed Loans (Details) - USD ($) $ in Billions	Dec. 31, 2017	Dec. 31, 2016
Consolidations and Transfers of Financial Assets [Abstract]
Securitized loans in unconsolidated portfolio securitization trusts: unpaid principal balance	$ 1.3	$ 1.4

Loans in Mortgage Portfolio (De

Loans in Mortgage Portfolio (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	$ 3,155,703	$ 3,063,646
Cost basis and fair value adjustments, net	41,906	39,572
Allowance for loan losses for loans held for investment	(19,084)	(23,465)	$ (27,951)	$ (35,541)
Total mortgage loans	3,178,525	3,079,753
Carrying value of loans redesignated from HFI to HFS	12,900	3,900	8,600
Carrying value of loans redesignated from HFS to HFI	113
Sale of loans, unpaid principal balance	12,200	6,700	3,600
Realized gains on sales of mortgage loans	723	54	$ 274
Single-Family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,890,634	2,833,750
Recorded investment of single-family mortgage loans referred to foreclosure	13,000	18,300
Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	$ 265,069	$ 229,896

Mortgage Loans Aging (Details)

Mortgage Loans Aging (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	$ 81,160	$ 74,222
Current, recorded investment	3,108,815	3,021,594
Total recorded investment in loans	3,189,975	3,095,816
Recorded investment in loans 90 days or more delinquent and accruing interest	303	285
Recorded investment in nonaccrual loans	45,323	42,108
30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	40,034	36,709
60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	11,975	9,564
Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	29,151	27,949
Single-Family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	80,858	74,049
Current, recorded investment	2,842,116	2,789,886
Total recorded investment in loans	2,922,974	2,863,935
Recorded investment in loans 90 days or more delinquent and accruing interest	303	285
Recorded investment in nonaccrual loans	$ 44,899	$ 41,705
Single-Family [Member] | Minimum [Member]
Table Footnote [Abstract]
Serious delinquency: days past due	90 days	90 days
Single-Family [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	$ 40,008	$ 36,665
Single-Family [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	11,975	9,564
Single-Family [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	28,875	27,820
Single-Family [Member] | Primary [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	69,977	61,302
Current, recorded investment	2,732,818	2,654,195
Total recorded investment in loans	2,802,795	2,715,497
Recorded investment in loans 90 days or more delinquent and accruing interest	87	22
Recorded investment in nonaccrual loans	37,971	33,448
Single-Family [Member] | Primary [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	35,582	31,631
Single-Family [Member] | Primary [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	10,396	7,910
Single-Family [Member] | Primary [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	23,999	21,761
Single-Family [Member] | Government [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	282	334
Current, recorded investment	30,807	36,814
Total recorded investment in loans	31,089	37,148
Recorded investment in loans 90 days or more delinquent and accruing interest	206	256
Recorded investment in nonaccrual loans	0	0
Single-Family [Member] | Government [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	55	56
Single-Family [Member] | Government [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	21	22
Single-Family [Member] | Government [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	206	256
Single-Family [Member] | Alt-A [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	7,751	9,044
Current, recorded investment	59,475	72,903
Total recorded investment in loans	67,226	81,947
Recorded investment in loans 90 days or more delinquent and accruing interest	5	2
Recorded investment in nonaccrual loans	5,094	6,019
Single-Family [Member] | Alt-A [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	3,186	3,629
Single-Family [Member] | Alt-A [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	1,147	1,194
Single-Family [Member] | Alt-A [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	3,418	4,221
Single-Family [Member] | Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	2,848	3,369
Current, recorded investment	19,016	25,974
Total recorded investment in loans	21,864	29,343
Recorded investment in loans 90 days or more delinquent and accruing interest	5	5
Recorded investment in nonaccrual loans	1,834	2,238
Single-Family [Member] | Other [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	1,185	1,349
Single-Family [Member] | Other [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	411	438
Single-Family [Member] | Other [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	1,252	1,582
Multifamily [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	302	173
Current, recorded investment	266,699	231,708
Total recorded investment in loans	267,001	231,881
Recorded investment in loans 90 days or more delinquent and accruing interest	0	0
Recorded investment in nonaccrual loans	$ 424	$ 403
Multifamily [Member] | Minimum [Member]
Table Footnote [Abstract]
Serious delinquency: days past due	60 days	60 days
Multifamily [Member] | Maximum [Member]
Table Footnote [Abstract]
Serious delinquency: days past due	89 days	89 days
Multifamily [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	$ 26	$ 44
Multifamily [Member] | Seriously Delinquent [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days delinquent, recorded investment	$ 276	$ 129

Mortgage Loans Credit Quality I

Mortgage Loans Credit Quality Indicators - SF (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	$ 3,189,975	$ 3,095,816
Single-Family [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	2,922,974	2,863,935
Single-Family [Member] | Primary [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	2,802,795	2,715,497
Single-Family [Member] | Primary [Member] | Estimated mark-to-market loan-to-value ratio less than or equal to 80% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	2,439,858	2,321,201
Single-Family [Member] | Primary [Member] | Estimated mark-to-market loan-to-value ratio greater than 80% and less than or equal to 90% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	238,038	244,231
Single-Family [Member] | Primary [Member] | Estimated mark-to-market loan-to-value ratio greater than 90% and less than or equal to 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	106,076	114,412
Single-Family [Member] | Primary [Member] | Estimated mark-to-market loan-to-value ratio greater than 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	18,823	35,653
Single-Family [Member] | Alt-A [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	67,226	81,947
Single-Family [Member] | Alt-A [Member] | Estimated mark-to-market loan-to-value ratio less than or equal to 80% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	51,903	56,250
Single-Family [Member] | Alt-A [Member] | Estimated mark-to-market loan-to-value ratio greater than 80% and less than or equal to 90% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	6,680	9,787
Single-Family [Member] | Alt-A [Member] | Estimated mark-to-market loan-to-value ratio greater than 90% and less than or equal to 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	4,044	6,731
Single-Family [Member] | Alt-A [Member] | Estimated mark-to-market loan-to-value ratio greater than 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	4,599	9,179
Single-Family [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	21,864	29,343
Single-Family [Member] | Other [Member] | Estimated mark-to-market loan-to-value ratio less than or equal to 80% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	16,428	19,382
Single-Family [Member] | Other [Member] | Estimated mark-to-market loan-to-value ratio greater than 80% and less than or equal to 90% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	2,277	3,657
Single-Family [Member] | Other [Member] | Estimated mark-to-market loan-to-value ratio greater than 90% and less than or equal to 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	1,443	2,627
Single-Family [Member] | Other [Member] | Estimated mark-to-market loan-to-value ratio greater than 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	1,716	3,677
Single-Family [Member] | Government [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	$ 31,089	$ 37,148

Mortgage Loans Credit Quality68

Mortgage Loans Credit Quality Indicators - MF (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	$ 3,189,975	$ 3,095,816
Multifamily [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	267,001	231,881
Multifamily [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	263,416	228,749
Multifamily [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	3,585	3,129
Multifamily [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	0	3
Multifamily [Member] | Total classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	$ 3,585	$ 3,132

Mortgage Loans Individually Imp

Mortgage Loans Individually Impaired Loans (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: unpaid principal balance	$ 123,314	$ 145,421
Individually impaired loans with related allowance recorded: total recorded investment	116,474	136,977
Related allowance for loan losses	(17,289)	(21,953)
Individually impaired loans with no related allowance recorded: unpaid principal balance	20,642	20,732
Individually impaired loans with no related allowance recorded: total recorded investment	19,307	19,210
Total individually impaired loans: unpaid principal balance	143,956	166,153
Total individually impaired loans: total recorded investment	135,781	156,187
Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: unpaid principal balance	123,035	145,101
Individually impaired loans with related allowance recorded: total recorded investment	116,194	136,654
Related allowance for loan losses	(17,247)	(21,920)
Individually impaired loans with no related allowance recorded: unpaid principal balance	20,334	20,466
Individually impaired loans with no related allowance recorded: total recorded investment	18,997	18,944
Single-Family [Member] | Primary [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: unpaid principal balance	91,194	105,113
Individually impaired loans with related allowance recorded: total recorded investment	86,864	99,825
Related allowance for loan losses	(11,652)	(14,462)
Individually impaired loans with no related allowance recorded: unpaid principal balance	16,027	15,733
Individually impaired loans with no related allowance recorded: total recorded investment	15,158	14,758
Single-Family [Member] | Government [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: unpaid principal balance	276	302
Individually impaired loans with related allowance recorded: total recorded investment	279	305
Related allowance for loan losses	(56)	(59)
Individually impaired loans with no related allowance recorded: unpaid principal balance	66	63
Individually impaired loans with no related allowance recorded: total recorded investment	60	59
Single-Family [Member] | Alt-A [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: unpaid principal balance	23,077	28,599
Individually impaired loans with related allowance recorded: total recorded investment	21,045	26,059
Related allowance for loan losses	(4,046)	(5,365)
Individually impaired loans with no related allowance recorded: unpaid principal balance	3,253	3,511
Individually impaired loans with no related allowance recorded: total recorded investment	2,870	3,062
Single-Family [Member] | Other [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: unpaid principal balance	8,488	11,087
Individually impaired loans with related allowance recorded: total recorded investment	8,006	10,465
Related allowance for loan losses	(1,493)	(2,034)
Individually impaired loans with no related allowance recorded: unpaid principal balance	988	1,159
Individually impaired loans with no related allowance recorded: total recorded investment	909	1,065
Multifamily [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: unpaid principal balance	279	320
Individually impaired loans with related allowance recorded: total recorded investment	280	323
Related allowance for loan losses	(42)	(33)
Individually impaired loans with no related allowance recorded: unpaid principal balance	308	266
Individually impaired loans with no related allowance recorded: total recorded investment	$ 310	$ 266

Mortgage Loans Individually I70

Mortgage Loans Individually Impaired Loans - 2 (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	$ 126,152	$ 144,792	$ 159,325
Individually impaired loans with related allowance recorded: total interest income recognized	4,987	5,420	5,628
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	394	399	393
Individually impaired loans with no related allowance recorded: average recorded investment	19,521	20,078	21,199
Individually impaired loans with no related allowance recorded: total interest income recognized	1,483	1,670	1,346
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	113	103	105
Individually impaired loans: average recorded investment	145,673	164,870	180,524
Individually impaired loans: total interest income recognized	6,470	7,090	6,974
Individually impaired loans: interest income recognized on a cash basis	507	502	498
Table Footnote [Abstract]
Individually impaired loans: total interest income recognized	6,470	7,090	6,974
Single Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	125,879	144,284	158,352
Individually impaired loans with related allowance recorded: total interest income recognized	4,978	5,391	5,612
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	394	399	393
Individually impaired loans with no related allowance recorded: average recorded investment	19,224	19,761	20,757
Individually impaired loans with no related allowance recorded: total interest income recognized	1,464	1,657	1,336
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	113	103	105
Individually impaired loans: total interest income recognized	6,400	7,000	6,900
Table Footnote [Abstract]
Troubled debt restructuring recorded investment	134,700	155,000
Individually impaired loans: total interest income recognized	6,400	7,000	6,900
Individually impaired loans: contractual interest income	5,500	5,700	5,700
Individually impaired loans: effective yield adjustments	925	1,300	1,200
Single Family [Member] | Primary [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	92,893	105,076	114,737
Individually impaired loans with related allowance recorded: total interest income recognized	3,721	4,004	4,190
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	319	325	318
Individually impaired loans with no related allowance recorded: average recorded investment	15,166	15,293	15,796
Individually impaired loans with no related allowance recorded: total interest income recognized	1,107	1,236	1,039
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	96	91	91
Single Family [Member] | Government [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	292	314	299
Individually impaired loans with related allowance recorded: total interest income recognized	10	12	12
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	0	0	0
Individually impaired loans with no related allowance recorded: average recorded investment	61	59	55
Individually impaired loans with no related allowance recorded: total interest income recognized	3	4	4
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	0	0	0
Single Family [Member] | Alt-A [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	23,536	27,512	30,453
Individually impaired loans with related allowance recorded: total interest income recognized	929	1,010	1,034
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	56	54	54
Individually impaired loans with no related allowance recorded: average recorded investment	3,000	3,293	3,647
Individually impaired loans with no related allowance recorded: total interest income recognized	270	309	218
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	13	9	11
Single Family [Member] | Other [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	9,158	11,382	12,863
Individually impaired loans with related allowance recorded: total interest income recognized	318	365	376
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	19	20	21
Individually impaired loans with no related allowance recorded: average recorded investment	997	1,116	1,259
Individually impaired loans with no related allowance recorded: total interest income recognized	84	108	75
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	4	3	3
Multifamily [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	273	508	973
Individually impaired loans with related allowance recorded: total interest income recognized	9	29	16
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	0	0	0
Individually impaired loans with no related allowance recorded: average recorded investment	297	317	442
Individually impaired loans with no related allowance recorded: total interest income recognized	19	13	10
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	0	0	$ 0
Table Footnote [Abstract]
Troubled debt restructuring recorded investment	$ 185	$ 248

Mortgage Loans TDRs (Details)

Mortgage Loans TDRs (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)contracts	Dec. 31, 2016USD ($)contracts	Dec. 31, 2015USD ($)contracts
Financing Receivable, Modifications [Line Items]
Average term extension of a single-family modified loan	153 months	157 months	161 months
Average interest rate reduction of a single-family modified loan	0.56%	0.79%	0.74%
Number of loans troubled debt restructurings activity | contracts	66,414	69,811	82,418
Recorded investment troubled debt restructurings activity | $	$ 9,342	$ 9,681	$ 11,487
Single-Family [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	66,406	69,800	82,406
Recorded investment troubled debt restructurings activity | $	$ 9,243	$ 9,615	$ 11,447
Single-Family [Member] | Primary [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	59,708	61,586	71,293
Recorded investment troubled debt restructurings activity | $	$ 8,247	$ 8,405	$ 9,713
Single-Family [Member] | Government [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	171	186	241
Recorded investment troubled debt restructurings activity | $	$ 18	$ 20	$ 27
Single-Family [Member] | Alt-A [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	5,369	6,647	9,037
Recorded investment troubled debt restructurings activity | $	$ 771	$ 946	$ 1,374
Single-Family [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	1,158	1,381	1,835
Recorded investment troubled debt restructurings activity | $	$ 207	$ 244	$ 333
Multifamily [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings activity | contracts	8	11	12
Recorded investment troubled debt restructurings activity | $	$ 99	$ 66	$ 40

Mortgage Loans TDRs with Sub De

Mortgage Loans TDRs with Sub Defaults (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)contracts	Dec. 31, 2016USD ($)contracts	Dec. 31, 2015USD ($)contracts
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	22,980	25,043	31,684
Recorded investment troubled debt restructurings subsequent default | $	$ 3,289	$ 3,667	$ 4,783
Single-Family [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	22,978	25,038	31,681
Recorded investment troubled debt restructurings subsequent default | $	$ 3,277	$ 3,621	$ 4,777
Single-Family [Member] | Primary [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	19,539	20,810	26,206
Recorded investment troubled debt restructurings subsequent default | $	$ 2,722	$ 2,938	$ 3,808
Single-Family [Member] | Government [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	91	95	118
Recorded investment troubled debt restructurings subsequent default | $	$ 10	$ 11	$ 16
Single-Family [Member] | Alt-A [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	2,588	3,131	4,128
Recorded investment troubled debt restructurings subsequent default | $	$ 400	$ 500	$ 706
Single-Family [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	760	1,002	1,229
Recorded investment troubled debt restructurings subsequent default | $	$ 145	$ 172	$ 247
Multifamily [Member]
Financing Receivable, Modifications [Line Items]
Number of loans troubled debt restructurings subsequent default | contracts	2	5	3
Recorded investment troubled debt restructurings subsequent default | $	$ 12	$ 46	$ 6

Allowance for Loan Losses Rollf

Allowance for Loan Losses Rollforward by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2015
Allowance for Loan Losses [Roll Forward]
Beginning balance	$ (23,465)	$ (27,951)	$ (35,541)
Benefit (provision) for loan losses	1,941	1,759	158
Charge-offs	2,798	3,266	9,774
Recoveries	(329)	(449)	(1,140)
Other	(29)	(90)	(1,202)
Ending balance	(19,084)	(23,465)	(27,951)
Natural Disasters and Other Casualty Events [Member]
Allowance for Loan Losses [Roll Forward]
Benefit (provision) for loan losses	900
Single-Family [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	(23,283)	(27,709)	(35,177)
Benefit (provision) for loan losses	1,994	1,704	68
Charge-offs	2,795	3,254	9,731
Recoveries	(326)	(442)	(1,136)
Other	(29)	(90)	(1,195)
Ending balance	(18,849)	(23,283)	(27,709)
Multifamily [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	(182)	(242)	(364)
Benefit (provision) for loan losses	(53)	55	90
Charge-offs	3	12	43
Recoveries	(3)	(7)	(4)
Other	0	0	(7)
Ending balance	$ (235)	$ (182)	$ (242)
Change in Accounting Method Accounted for as Change in Estimate [Member]
Table Footnote [Abstract]
Advisory Bulletin impact for HFI loans				$ 1,800
Advisory Bulletin impact for preforeclosure property taxes and insurance receivable				724
Nonaccrual Policy [Member]
Table Footnote [Abstract]
Allowance for accrued interest receivables: charge-offs				$ 1,100

Allowance for Loan Losses and T

Allowance for Loan Losses and Total Recorded Investment in HFI Loans (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses for individually impaired loans	$ (17,289)	$ (21,953)
Allowance for loan losses for collectively reserved loans	(1,795)	(1,512)
Total allowance for loan losses	(19,084)	(23,465)	$ (27,951)	$ (35,541)
Recorded investment in individually impaired loans	135,781	156,187
Recorded investment in collectively reserved loans	3,054,194	2,939,629
Total recorded investment in loans	3,189,975	3,095,816
Single-Family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses for individually impaired loans	(17,247)	(21,920)
Allowance for loan losses for collectively reserved loans	(1,602)	(1,363)
Total allowance for loan losses	(18,849)	(23,283)	(27,709)	(35,177)
Recorded investment in individually impaired loans	135,191	155,598
Recorded investment in collectively reserved loans	2,787,783	2,708,337
Total recorded investment in loans	2,922,974	2,863,935
Multifamily [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses for individually impaired loans	(42)	(33)
Allowance for loan losses for collectively reserved loans	(193)	(149)
Total allowance for loan losses	(235)	(182)	$ (242)	$ (364)
Recorded investment in individually impaired loans	590	589
Recorded investment in collectively reserved loans	266,411	231,292
Total recorded investment in loans	$ 267,001	$ 231,881

Investments in Securities Tradi

Investments in Securities Trading 1 (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	$ 34,679	$ 40,562
Mortgage-related securities [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	5,457	8,245
Fannie Mae [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	3,876	4,769
Other agency [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	1,118	2,058
Alt-A and subprime private-label securities [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	453	636
Commerical mortgage-backed securities (CMBS) [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	9	761
Mortgage revenue bonds [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	1	21
U.S. Treasury Securities [Member]
Schedule of Investments in Trading Securities [Line Items]
Trading, at fair value	$ 29,222	$ 32,317

Investments in Securities Tra76

Investments in Securities Trading 2 (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Net trading gains (losses)	$ 190	$ 28	$ (368)
Net trading gains (losses) recognized in the period related to securities still held at period end	$ 161	$ (19)	$ (453)

Investments in Securities Avail

Investments in Securities Available-for-sale Securities 1 (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Gross realized gains	$ 487	$ 1,043	$ 1,066
Gross realized losses	1	17	70
Total proceeds (excludes initial sale of securities from new portfolio securitizations)	$ 1,780	$ 10,993	$ 8,023

Investments in Securities Ava78

Investments in Securities Available-for-sale Securities 2 (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	$ 4,058	$ 7,261
Gross unrealized gains	816	1,142
Gross unrealized losses	(31)	(40)
Total fair value	4,843	8,363
Fannie Mae [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	2,044	2,445
Gross unrealized gains	102	137
Gross unrealized losses	(27)	(28)
Total fair value	2,119	2,554
Other agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	332	508
Gross unrealized gains	25	39
Gross unrealized losses	0	0
Total fair value	357	547
Alt-A and subprime private-label securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	662	1,817
Gross unrealized gains	652	895
Gross unrealized losses	0	(3)
Total fair value	1,314	2,709
CMBS [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	15	815
Gross unrealized gains	0	4
Gross unrealized losses	0	0
Total fair value	15	819
Mortgage revenue bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	655	1,245
Gross unrealized gains	20	36
Gross unrealized losses	(4)	(9)
Total fair value	671	1,272
Other mortgage-related securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	350	431
Gross unrealized gains	17	31
Gross unrealized losses	0	0
Total fair value	$ 367	$ 462

Investments in Securities Ava79

Investments in Securities Available-for-sale Securities 3 (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Consecutive Months, Gross Unrealized Losses	$ (1)	$ (9)
Less Than 12 Consecutive Months, Fair Value	134	217
12 Consecutive Months or Longer, Gross Unrealized Losses	(30)	(31)
12 Consecutive Months or Longer, Fair Value	464	556
Fannie Mae [Member]
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Consecutive Months, Gross Unrealized Losses	(1)	(2)
Less Than 12 Consecutive Months, Fair Value	134	139
12 Consecutive Months or Longer, Gross Unrealized Losses	(26)	(26)
12 Consecutive Months or Longer, Fair Value	461	477
Alt-A and subprime private-label securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Consecutive Months, Gross Unrealized Losses		0
Less Than 12 Consecutive Months, Fair Value		0
12 Consecutive Months or Longer, Gross Unrealized Losses		(3)
12 Consecutive Months or Longer, Fair Value		73
Mortgage revenue bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Consecutive Months, Gross Unrealized Losses	0	(7)
Less Than 12 Consecutive Months, Fair Value	0	78
12 Consecutive Months or Longer, Gross Unrealized Losses	(4)	(2)
12 Consecutive Months or Longer, Fair Value	$ 3	$ 6

Investments in Securities Other

Investments in Securities Other-than-temporary Impairments 1 (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Other than Temporary Impairments, Amount	$ 5	$ 35	$ 196
Available-for-sale securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held	$ 1,100	$ 1,900	$ 2,400

Investments in Securities Matur

Investments in Securities Maturity Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturity
Total amortized cost	$ 4,058	$ 7,261
Total fair value	4,843	8,363
One Year or Less, Amortized Cost	34
One Year or Less, Fair Value	34
After One Year through Five Years, Amortized Cost	102
After One Year through Five Years, Fair Value	102
After Five Years through Ten Years, Amortized Cost	204
After Five Years through Ten Years, Fair Value	214
After Ten Years, Amortized Cost	3,718
After Ten Years, Fair Value	$ 4,493
Weighted average yield	6.84%
One Year or Less, weighted average yield	4.18%
After One Year through Five Years, weighted average yield	6.60%
After Five Years through Ten Years, weighted average yield	6.59%
After Ten Years, weighted average yield	6.88%
Fannie Mae [Member]
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturity
Total amortized cost	$ 2,044	2,445
Total fair value	2,119	2,554
One Year or Less, Amortized Cost	2
One Year or Less, Fair Value	2
After One Year through Five Years, Amortized Cost	12
After One Year through Five Years, Fair Value	12
After Five Years through Ten Years, Amortized Cost	59
After Five Years through Ten Years, Fair Value	63
After Ten Years, Amortized Cost	1,971
After Ten Years, Fair Value	2,042
Other agency [Member]
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturity
Total amortized cost	332	508
Total fair value	357	547
One Year or Less, Amortized Cost	2
One Year or Less, Fair Value	2
After One Year through Five Years, Amortized Cost	15
After One Year through Five Years, Fair Value	15
After Five Years through Ten Years, Amortized Cost	57
After Five Years through Ten Years, Fair Value	61
After Ten Years, Amortized Cost	258
After Ten Years, Fair Value	279
Alt-A and subprime private-label securities [Member]
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturity
Total amortized cost	662	1,817
Total fair value	1,314	2,709
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	0
After One Year through Five Years, Fair Value	0
After Five Years through Ten Years, Amortized Cost	0
After Five Years through Ten Years, Fair Value	0
After Ten Years, Amortized Cost	662
After Ten Years, Fair Value	1,314
CMBS [Member]
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturity
Total amortized cost	15	815
Total fair value	15	819
One Year or Less, Amortized Cost	15
One Year or Less, Fair Value	15
After One Year through Five Years, Amortized Cost	0
After One Year through Five Years, Fair Value	0
After Five Years through Ten Years, Amortized Cost	0
After Five Years through Ten Years, Fair Value	0
After Ten Years, Amortized Cost	0
After Ten Years, Fair Value	0
Mortgage revenue bonds [Member]
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturity
Total amortized cost	655	1,245
Total fair value	671	1,272
One Year or Less, Amortized Cost	15
One Year or Less, Fair Value	15
After One Year through Five Years, Amortized Cost	75
After One Year through Five Years, Fair Value	75
After Five Years through Ten Years, Amortized Cost	83
After Five Years through Ten Years, Fair Value	85
After Ten Years, Amortized Cost	482
After Ten Years, Fair Value	496
Other mortgage-related securities [Member]
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturity
Total amortized cost	350	431
Total fair value	367	$ 462
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	0
After One Year through Five Years, Fair Value	0
After Five Years through Ten Years, Amortized Cost	5
After Five Years through Ten Years, Fair Value	5
After Ten Years, Amortized Cost	345
After Ten Years, Fair Value	$ 362

Financial Guarantees and Maximu

Financial Guarantees and Maximum Recovery (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Financial Guarantees and Maximum Recovery [Line Items]
Maximum exposure	$ 25,141	$ 27,942
Guaranty obligation	258	280
Maximum recovery	9,744	10,711
Unconsolidated VIEs [Member] | Unconsolidated Fannie Mae MBS [Member]
Financial Guarantees and Maximum Recovery [Line Items]
Maximum exposure	10,876	12,607
Guaranty obligation	127	143
Maximum recovery	7,340	8,048
Unconsolidated VIEs [Member] | Other guaranty arrangements [Member]
Financial Guarantees and Maximum Recovery [Line Items]
Maximum exposure	14,265	15,335
Guaranty obligation	131	137
Maximum recovery	$ 2,404	$ 2,663
Minimum [Member]
Financial Guarantees and Maximum Recovery [Line Items]
Contractual terms of our guarantees	5 days
Maximum [Member]
Financial Guarantees and Maximum Recovery [Line Items]
Contractual terms of our guarantees	35 years

Short-Term Debt (Details)

Short-Term Debt (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Short-Term Debt [Line Items]
Short-term debt, outstanding	$ 33,756,000,000	$ 35,579,000,000
Short-term debt, weighted-average interest rate	1.18%	0.49%
Line of Credit [Member]
Short-Term Debt [Line Items]
Line of credit maximum borrowing capacity	$ 15,000,000,000	$ 15,000,000,000
Consolidated Trusts [Member]
Short-Term Debt [Line Items]
Short-term debt, outstanding	$ 379,000,000	$ 584,000,000
Short-term debt, weighted-average interest rate	1.11%	0.48%
Fannie Mae [Member]
Short-Term Debt [Line Items]
Short-term debt, outstanding	$ 33,377,000,000	$ 34,995,000,000
Short-term debt, weighted-average interest rate	1.18%	0.49%

Long-Term Debt (Details)

Long-Term Debt (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 3,296,298	$ 3,226,737
Long-term debt, weighted-average interest rate	2.77%	2.54%
Consolidated Trusts [Member]
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 3,052,923	$ 2,934,635
Long-term debt, weighted-average interest rate	2.80%	2.57%
Fannie Mae [Member]
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 243,375	$ 292,102
Long-term debt, weighted-average interest rate	2.40%	2.31%
Net unamortized discount, fair value adjustments and other cost basis adjustments	$ 752	$ 1,800
Fannie Mae [Member] | Minimum [Member]
Long-Term Debt [Line Items]
Medium-term notes original contractual maturity	1 year	1 year
Long-term debt original contractual maturity greater than 10 years	10 years	10 years
Fannie Mae [Member] | Maximum [Member]
Long-Term Debt [Line Items]
Medium-term notes original contractual maturity	10 years	10 years
Fannie Mae [Member] | Senior Fixed [Member]
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 206,863	$ 249,013
Long-term debt, weighted-average interest rate	1.95%	2.14%
Fannie Mae [Member] | Senior fixed benchmark notes and bonds [Member]
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 123,541	$ 153,983
Long-term debt, weighted-average interest rate	2.11%	2.16%
Fannie Mae [Member] | Senior fixed medium-term notes [Member]
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 75,901	$ 82,230
Long-term debt, weighted-average interest rate	1.41%	1.40%
Fannie Mae [Member] | Senior fixed other debt [Member]
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 7,421	$ 12,800
Long-term debt, weighted-average interest rate	4.84%	6.74%
Fannie Mae [Member] | Senior floating [Member]
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 31,328	$ 38,333
Long-term debt, weighted-average interest rate	4.14%	2.48%
Fannie Mae [Member] | Senior floating medium-term notes [Member]
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 8,425	$ 21,476
Long-term debt, weighted-average interest rate	1.36%	0.71%
Fannie Mae [Member] | Senior floating Connecticut Avenue Securities [Member]
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 22,527	$ 16,511
Long-term debt, weighted-average interest rate	5.18%	4.77%
Fannie Mae [Member] | Senior floating other debt [Member]
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 376	$ 346
Long-term debt, weighted-average interest rate	6.36%	6.75%
Fannie Mae [Member] | Subordinated debentures [Member]
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 5,106	$ 4,645
Long-term debt, weighted-average interest rate	9.93%	9.93%
Fannie Mae [Member] | Secured borrowings [Member]
Long-Term Debt [Line Items]
Long-term debt, outstanding	$ 78	$ 111
Long-term debt, weighted-average interest rate	1.70%	1.44%

Short-Term and Long-Term Debt C

Short-Term and Long-Term Debt Characteristics of Debt (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Long-Term Debt by Year of Maturity [Abstract]
Total long-term debt	$ 3,296,298	$ 3,226,737
Consolidated Trusts [Member]
Long-Term Debt by Year of Maturity [Abstract]
Total long-term debt	3,052,923	2,934,635
Earlier of Contractual Maturity or Next Call Date [Member]
Long-Term Debt by Year of Maturity [Abstract]
Total long-term debt	3,296,298
Earlier of Contractual Maturity or Next Call Date [Member] | Consolidated Trusts [Member]
Long-Term Debt by Year of Maturity [Abstract]
Total long-term debt	3,052,923
Fannie Mae [Member]
Long-Term Debt [Line Items]
Face amount	277,500	328,900
Long-Term Debt by Year of Maturity [Abstract]
2,018	53,932
2,019	61,760
2,020	39,712
2,021	23,945
2,022	8,463
Thereafter	55,563
Total long-term debt	243,375	292,102
Net unamortized discount, fair value adjustments and other cost basis adjustments	752	1,800
Fannie Mae [Member] | Zero-Coupon Debt [Member]
Long-Term Debt [Line Items]
Face amount	$ 39,800	$ 45,900
Effective interest rate	2.29%	2.43%
Fannie Mae [Member] | Callable [Member]
Long-Term Debt [Line Items]
Outstanding debt	$ 72,300	$ 77,300
Fannie Mae [Member] | Earlier of Contractual Maturity or Next Call Date [Member]
Long-Term Debt by Year of Maturity [Abstract]
2,018	100,446
2,019	45,015
2,020	25,202
2,021	14,184
2,022	7,353
Thereafter	51,175
Total long-term debt	$ 243,375

Derivative Instruments Derivati

Derivative Instruments Derivatives 1 - Notional and FV Position (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Asset Derivatives [Abstract]
Notional amount	$ 178,138	$ 156,763
Derivative asset, estimated fair value	171	687
Netting adjustment	(4,272)	(4,514)
Derivative Liabilities [Abstract]
Notional amount	338,089	339,456
Derivative liability, estimated fair value	(328)	(1,215)
Netting adjustment	4,979	6,844
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	1,400	2,900
Cash collateral received for derivative instruments	649	535
Pay-fixed swap
Asset Derivatives [Abstract]
Notional amount	52,732	29,540
Derivative asset, estimated fair value	772	660
Derivative Liabilities [Abstract]
Notional amount	70,211	94,584
Derivative liability, estimated fair value	(2,120)	(4,396)
Receive-fixed Swap
Asset Derivatives [Abstract]
Notional amount	31,671	30,207
Derivative asset, estimated fair value	2,391	2,696
Derivative Liabilities [Abstract]
Notional amount	138,852	135,470
Derivative liability, estimated fair value	(1,764)	(1,552)
Basis swap
Asset Derivatives [Abstract]
Notional amount	873	1,624
Derivative asset, estimated fair value	124	115
Derivative Liabilities [Abstract]
Notional amount	0	15,600
Derivative liability, estimated fair value	0	(11)
Foreign currency swap
Asset Derivatives [Abstract]
Notional amount	234	214
Derivative asset, estimated fair value	59	40
Derivative Liabilities [Abstract]
Notional amount	236	216
Derivative liability, estimated fair value	(56)	(85)
Pay-fixed swaption
Asset Derivatives [Abstract]
Notional amount	9,750	9,600
Derivative asset, estimated fair value	95	241
Derivative Liabilities [Abstract]
Notional amount	4,000	4,850
Derivative liability, estimated fair value	(20)	(82)
Receive-fixed swaption
Asset Derivatives [Abstract]
Notional amount	250	0
Derivative asset, estimated fair value	13	0
Derivative Liabilities [Abstract]
Notional amount	9,250	10,100
Derivative liability, estimated fair value	(304)	(257)
Other
Asset Derivatives [Abstract]
Notional amount	13,240	15,087
Derivative asset, estimated fair value	22	33
Derivative Liabilities [Abstract]
Notional amount	7,315	655
Derivative liability, estimated fair value	(1)	(2)
Risk management derivatives
Asset Derivatives [Abstract]
Notional amount	108,750	86,272
Derivative asset, estimated fair value	3,476	3,785
Accrued interest receivable	835	785
Netting adjustment	(4,272)	(4,514)
Total net risk management derivatives - Asset	39	56
Derivative Liabilities [Abstract]
Notional amount	229,864	261,475
Derivative liability, estimated fair value	(4,265)	(6,385)
Accrued interest payable	(814)	(937)
Netting adjustment	4,979	6,844
Total net risk management derivatives - Liability	(100)	(478)
Mortgage commitments to purchase whole loans
Asset Derivatives [Abstract]
Notional amount	4,143	4,753
Derivative asset, estimated fair value	9	28
Derivative Liabilities [Abstract]
Notional amount	1,570	3,039
Derivative liability, estimated fair value	(2)	(49)
Forward contracts to purchase mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	45,925	31,635
Derivative asset, estimated fair value	108	198
Derivative Liabilities [Abstract]
Notional amount	21,099	27,297
Derivative liability, estimated fair value	(21)	(388)
Forward contracts to sell mortgage-related securities
Asset Derivatives [Abstract]
Notional amount	19,320	34,103
Derivative asset, estimated fair value	15	405
Derivative Liabilities [Abstract]
Notional amount	85,556	47,645
Derivative liability, estimated fair value	(205)	(300)
Mortgage commitment derivatives
Asset Derivatives [Abstract]
Notional amount	69,388	70,491
Derivative asset, estimated fair value	132	631
Netting adjustment	0	0
Derivative Liabilities [Abstract]
Notional amount	108,225	77,981
Derivative liability, estimated fair value	(228)	(737)
Netting adjustment	$ 0	$ 0

Derivative Instruments Deriva87

Derivative Instruments Derivatives 2 - FV Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									$ (1,185)	$ (835)	$ (1,513)
Net accrual of periodic settlements	$ 5,111	$ 5,274	$ 5,002	$ 5,346	$ 5,805	$ 5,435	$ 5,286	$ 4,769	20,733	21,295	21,409
Pay-fixed swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									1,296	757	(746)
Receive-fixed Swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									(851)	(751)	625
Basis swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									21	(21)	4
Foreign currency swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									49	(76)	(60)
Pay-fixed swaption
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									(161)	163	135
Receive-fixed swaption
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									(60)	(230)	(93)
Other
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									13	160	(25)
Risk management derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									(582)	(1,123)	(1,120)
Net accrual of periodic settlements									(889)	(1,125)	(960)
Mortgage commitment derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative fair value gains (losses), net									$ (603)	$ 288	$ (393)

Income Taxes Provision (Benefit

Income Taxes Provision (Benefit) for Income Taxes (Details) - USD ($) $ in Millions	Jan. 01, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Provision (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Current income tax benefit (provision)										$ 600	$ (2,014)	$ 271
Deferred income tax provision										(16,584)	(4,006)	(5,524)
Provision for federal income taxes		$ (11,489)	$ (1,525)	$ (1,587)	$ (1,383)	$ (2,545)	$ (1,527)	$ (1,398)	$ (550)	(15,984)	$ (6,020)	$ (5,253)
Income Taxes Receivable		$ 3,700								$ 3,700
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
Statutory corporate tax rate	21.00%									35.00%	35.00%	35.00%
Equity investments in affordable housing projects										(1.40%)	(1.90%)	(2.60%)
Effect of corporate tax rate change										53.60%	0.00%	0.00%
Other										(0.60%)	(0.30%)	0.90%
Valuation allowance										0.00%	0.00%	(0.90%)
Effective tax rate										86.60%	32.80%	32.40%

Income Taxes Deferred Tax Asset

Income Taxes Deferred Tax Assets and Liabilities (Details) - USD ($)	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Statutory corporate tax rate	21.00%	35.00%	35.00%	35.00%
Deferred Tax Assets, Operating Loss Carryforwards		$ 0
Deferred Tax Assets, Tax Credit Carryforwards		1,700,000,000
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax		837,000,000
Deferred tax assets:
Mortgage and mortgage-related assets		10,397,000,000	$ 17,130,000,000
Allowance for loan losses and basis in acquired property, net		2,286,000,000	9,496,000,000
Debt and derivative instruments		1,205,000,000	2,989,000,000
Partnership credits		1,695,000,000	1,968,000,000
Partnership and other equity investments		311,000,000	667,000,000
Other, net		1,621,000,000	1,665,000,000
Total deferred tax assets		17,515,000,000	33,915,000,000
Deferred tax liabilities:
Unrealized gains on AFS securities, net		165,000,000	385,000,000
Total deferred tax liabilities		165,000,000	385,000,000
Net deferred tax assets		$ 17,350,000,000	$ 33,530,000,000

Income Taxes Unrecognized Tax B

Income Taxes Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions	$ 514	$ 0	$ 0
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits as of January 1	0	0	213
Gross decreases- tax positions in prior years	0	0	(213)
Unrecognized tax benefits as of December 31	514	0	$ 0
Unrecognized Tax Benefit Resulting in Tax Credits and/or Net Operating Loss Carryforward	220	$ 0
Decrease in Unrecognized Tax Benefits is Reasonably Possible	$ 205

Segment Reporting (Narrative) (

Segment Reporting (Narrative) (Details)	12 Months Ended
	Dec. 31, 2017segments
Segment Reporting [Abstract]
Number of Reportable Segments	2

Segment Reporting Assets (Detai

Segment Reporting Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 3,345,529	$ 3,287,968	$ 3,221,917
Operating Segments [Member] | Single-Family [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	3,057,904	3,029,727	2,993,495
Operating Segments [Member] | Multifamily [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 287,625	$ 258,241	$ 228,422

Segment Reporting (Details)

Segment Reporting (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net interest income	$ 5,111	$ 5,274	$ 5,002	$ 5,346	$ 5,805	$ 5,435	$ 5,286	$ 4,769	$ 20,733	$ 21,295	$ 21,409
Fee and other income									2,227	966	1,348
Net revenues									22,960	22,261	22,757
Investment gains, net	833	313	385	(9)	322	467	398	69	1,522	1,256	1,336
Fair value losses, net	(191)	(289)	(691)	(40)	3,890	(491)	(1,667)	(2,813)	(1,211)	(1,081)	(1,767)
Administrative expenses	(703)	(664)	(686)	(684)	(714)	(661)	(678)	(688)	(2,737)	(2,741)	(3,050)
Benefit for credit losses	560	(182)	1,267	396	(1,303)	673	1,601	1,184	2,041	2,155	795
Foreclosed property income (expense)	(130)	(140)	(34)	(217)	(137)	(110)	(63)	(334)	(521)	(644)	(1,629)
Credit-related income (expense)									1,520	1,511	(834)
Temporary Payroll Cut Continuation Act of 2011 (TCCA) fees	(544)	(531)	(518)	(503)	(487)	(465)	(453)	(440)	(2,096)	(1,845)	(1,621)
Other expenses, net	(411)	(427)	(291)	(382)	(210)	(300)	(254)	(264)	(1,511)	(1,028)	(613)
Income before federal income taxes	4,956	4,548	4,787	4,156	7,580	4,723	4,344	1,686	18,447	18,333	16,208
Provision for federal income taxes	(11,489)	(1,525)	(1,587)	(1,383)	(2,545)	(1,527)	(1,398)	(550)	(15,984)	(6,020)	(5,253)
Net income											10,955
Less: Net income attributable to noncontrolling interest									0	0	(1)
Net income attributable to Fannie Mae	$ (6,533)	$ 3,023	$ 3,200	$ 2,773	$ 5,035	$ 3,196	$ 2,946	$ 1,136	2,463	12,313	10,954
US Treasury [Member]
Segment Reporting Information [Line Items]
Temporary Payroll Cut Continuation Act of 2011 (TCCA) fees									(2,096)	(1,845)	(1,621)
Operating Segments [Member] | Single-Family [Member]
Segment Reporting Information [Line Items]
Net interest income									18,212	19,010	19,301
Fee and other income									1,378	521	636
Net revenues									19,590	19,531	19,937
Investment gains, net									1,352	944	970
Fair value losses, net									(1,188)	(1,040)	(1,505)
Administrative expenses									(2,391)	(2,418)	(2,711)
Benefit for credit losses									2,090	2,092	688
Foreclosed property income (expense)									(540)	(653)	(1,723)
Credit-related income (expense)									1,550	1,439	(1,035)
Other expenses, net									(1,004)	(1,012)	(831)
Income before federal income taxes									15,813	15,599	13,204
Provision for federal income taxes									(14,301)	(5,417)	(4,593)
Net income											8,611
Less: Net income attributable to noncontrolling interest											0
Net income attributable to Fannie Mae									1,512	10,182	8,611
Operating Segments [Member] | Multifamily [Member]
Segment Reporting Information [Line Items]
Net interest income									2,521	2,285	2,108
Fee and other income									849	445	712
Net revenues									3,370	2,730	2,820
Investment gains, net									170	312	366
Fair value losses, net									(23)	(41)	(262)
Administrative expenses									(346)	(323)	(339)
Benefit for credit losses									(49)	63	107
Foreclosed property income (expense)									19	9	94
Credit-related income (expense)									(30)	72	201
Other expenses, net									(507)	(16)	218
Income before federal income taxes									2,634	2,734	3,004
Provision for federal income taxes									(1,683)	(603)	(660)
Net income											2,344
Less: Net income attributable to noncontrolling interest											(1)
Net income attributable to Fannie Mae									951	2,131	2,343
Operating Segments [Member] | US Treasury [Member] | Single-Family [Member]
Segment Reporting Information [Line Items]
Temporary Payroll Cut Continuation Act of 2011 (TCCA) fees									(2,096)	(1,845)	(1,621)
Operating Segments [Member] | US Treasury [Member] | Multifamily [Member]
Segment Reporting Information [Line Items]
Temporary Payroll Cut Continuation Act of 2011 (TCCA) fees									$ 0	$ 0	$ 0

Equity (Deficit) Narratives (De

Equity (Deficit) Narratives (Details)	Dec. 30, 2017USD ($)	Dec. 29, 2017USD ($)	Sep. 08, 2008USD ($)$ / shares	Sep. 08, 2008USD ($)$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)shares	Dec. 31, 2015USD ($)	Dec. 31, 2018USD ($)	Mar. 31, 2018USD ($)	Jan. 01, 2018USD ($)	Sep. 30, 2017USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Mar. 31, 2013USD ($)	Sep. 07, 2008$ / shares
Class of Stock [Line Items]
Common stock outstanding | shares					1,158,087,567	1,158,082,750
Percentage of common shares attributable to warrants issued to Treasury as a percentage to total diluted common shares upon exercise of the right					79.90%
Dividends declared on our senior preferred stock					$ 12,015,000,000	$ 9,624,000,000	$ 10,278,000,000
Net worth (deficit)					(3,686,000,000)	6,071,000,000	4,059,000,000				$ 3,600,000,000	$ 3,720,000,000
Payment Of Cash Dividends On Senior Preferred Stock To Treasury		$ 648,000,000			$ 12,015,000,000	9,624,000,000	10,278,000,000
Convertible Series 2004-1 Preferred Stock [Member]
Class of Stock [Line Items]
Conversion price per share | $ / shares					$ 94.31
Conversion rate					1,060.3329
Preferred stock redemption price per share | $ / shares					$ 105,000
Series 2008-2 Senior Preferred Stock [Member]
Class of Stock [Line Items]
Senior preferred stock liquidation preference per share | $ / shares			$ 1,000	$ 1,000	$ 117,149
Shares of variable liquidation preference senior preferred stock issued | shares				1,000,000
Aggregate liquidation preference of senior preferred stock			$ 1,000,000,000	$ 1,000,000,000
Value assigned to Treasury's commitment and recorded as a reduction to additional paid-in-capital			$ 4,500,000,000
Dividends declared on our senior preferred stock					$ 12,000,000,000	9,600,000,000	10,300,000,000
Preferred Stock Covenant Maximum Fair Market Value of assets and properties per transaction					250,000,000
Preferred Stock, Covenant, Maximum Aggregate Indebtedness Amount, Current Period					$ 407,200,000,000
Preferred Stock, Covenant, Current Period Debt v.s. Maximum Mortgage Assets Allowed at Prior Year End, Maximum Ratio					120.00%
Preferred Stock, Covenant, Maximum Mortgage Assets					$ 288,400,000,000
Payment Of Cash Dividends On Senior Preferred Stock To Treasury	$ 648,000,000
Minimum [Member] | Series O Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock redemption price per share | $ / shares					$ 50
Minimum [Member] | Series 2008-2 Senior Preferred Stock [Member]
Class of Stock [Line Items]
FHFA Request, Covenant, Mortgage Assets at Year End, Minimum Ratio of Preceding Year End					90.00%
Maximum [Member] | Series O Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock redemption price per share | $ / shares					$ 52.5
Maximum [Member] | Series 2008-2 Senior Preferred Stock [Member]
Class of Stock [Line Items]
FHFA Request, Covenant, Mortgage Assets at Year End, Minimum Ratio of Preceding Year End					95.00%
Scenario, Forecast [Member] | Series 2008-2 Senior Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Covenant, Maximum Mortgage Assets								$ 250,000,000,000
US Treasury [Member]
Class of Stock [Line Items]
Percentage of common shares attributable to warrants issued to Treasury as a percentage to total diluted common shares upon exercise of the right					79.90%										79.90%
Additional Liquidation Preference of Senior Preferred Stock					$ 3,000,000,000
Aggregate liquidation preference of senior preferred stock					120,100,000,000
Aggregate funding received from US Treasury pursuant to the senior preferred stock purchase agreement					116,100,000,000	116,100,000,000
Funding Draw Requested From U.S. Treasury Pursuant to the Senior Preferred Stock Purchase Agreement					3,700,000,000
Capital reserve amount for the fiscal year based on the amended Senior Preferred Stock Purchase agreement					600,000,000	1,200,000,000				$ 0	$ 600,000,000		$ 3,000,000,000
Annual Reduction of Capital Reserve Amount from 2013 to 2017, Senior Preferred Stock Purchase Agreement, Amendment					600,000,000	$ 600,000,000	$ 600,000,000							$ 600,000,000
Common stock warrant exercise price per share | $ / shares															$ 0.00001
Total remaining funding available from US Treasury pursuant to the senior preferred stock agreement					117,600,000,000
Reduction in Dividends Paid					$ 2,400,000,000
US Treasury [Member] | Scenario, Forecast [Member]
Class of Stock [Line Items]
Aggregate liquidation preference of senior preferred stock									$ 123,800,000,000
Aggregate funding received from US Treasury pursuant to the senior preferred stock purchase agreement									119,800,000,000
Capital Reserve Amount, Fiscal Year, Senior Preferred Stock Purchase Agreement, December 2017 Amendment										$ 3,000,000,000
Total remaining funding available from US Treasury pursuant to the senior preferred stock agreement									$ 113,900,000,000

Equity (Deficit) Schedule of St

Equity (Deficit) Schedule of Stock by Class (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Jan. 01, 2018	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2013	Mar. 31, 2013	Sep. 08, 2008	Jun. 04, 2008	May 22, 2008	May 19, 2008	Dec. 14, 2007	Nov. 21, 2007
Class of Stock [Line Items]
Senior preferred stock issued, shares	1,000,000			1,000,000
Senior preferred stock value	$ 117,149,000,000			$ 117,149,000,000
Senior preferred stock, shares outstanding	1,000,000			1,000,000
Preferred stock, shares issued	555,374,922			555,374,922
Preferred stock issued, amount	$ 19,130,000,000			$ 19,130,000,000
Preferred stock, shares outstanding	555,374,922			555,374,922
Preferred stock outstanding, amount	$ 19,130,000,000			$ 19,130,000,000
Series 2008-2 Senior Preferred Stock [Member]
Class of Stock [Line Items]
Senior preferred stock issued, shares	1,000,000			1,000,000
Senior preferred stock value	$ 117,149,000,000			$ 117,149,000,000				$ 1,000,000,000
Senior preferred stock, shares outstanding	1,000,000			1,000,000
Senior preferred stock, stated value per share	$ 117,149							$ 1,000
Series D Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	3,000,000			3,000,000
Preferred stock issued, amount	$ 150,000,000			$ 150,000,000
Preferred stock, shares outstanding	3,000,000			3,000,000
Preferred stock outstanding, amount	$ 150,000,000			$ 150,000,000
Preferred stock, stated value per share	$ 50
Preferred stock, annual dividend rate (as a percent)	5.25%
Series E Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	3,000,000			3,000,000
Preferred stock issued, amount	$ 150,000,000			$ 150,000,000
Preferred stock, shares outstanding	3,000,000			3,000,000
Preferred stock outstanding, amount	$ 150,000,000			$ 150,000,000
Preferred stock, stated value per share	$ 50
Preferred stock, annual dividend rate (as a percent)	5.10%
Series F Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	14,000,000			14,000,000
Preferred stock issued, amount	$ 690,000,000			$ 690,000,000
Preferred stock, shares outstanding	14,000,000			14,000,000
Preferred stock outstanding, amount	$ 690,000,000			$ 690,000,000
Preferred stock, stated value per share	$ 50
Preferred stock, annual dividend rate (as a percent)	0.73%
Preferred Stock, Redemption Terms	P2Y
Series G Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	6,000,000			6,000,000
Preferred stock issued, amount	$ 288,000,000			$ 288,000,000
Preferred stock, shares outstanding	6,000,000			6,000,000
Preferred stock outstanding, amount	$ 288,000,000			$ 288,000,000
Preferred stock, stated value per share	$ 50
Preferred stock, annual dividend rate (as a percent)	0.61%
Preferred Stock, Redemption Terms	P2Y
Series H Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	8,000,000			8,000,000
Preferred stock issued, amount	$ 400,000,000			$ 400,000,000
Preferred stock, shares outstanding	8,000,000			8,000,000
Preferred stock outstanding, amount	$ 400,000,000			$ 400,000,000
Preferred stock, stated value per share	$ 50
Preferred stock, annual dividend rate (as a percent)	5.81%
Series I Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	6,000,000			6,000,000
Preferred stock issued, amount	$ 300,000,000			$ 300,000,000
Preferred stock, shares outstanding	6,000,000			6,000,000
Preferred stock outstanding, amount	$ 300,000,000			$ 300,000,000
Preferred stock, stated value per share	$ 50
Preferred stock, annual dividend rate (as a percent)	5.375%
Series L Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	7,000,000			7,000,000
Preferred stock issued, amount	$ 345,000,000			$ 345,000,000
Preferred stock, shares outstanding	7,000,000			7,000,000
Preferred stock outstanding, amount	$ 345,000,000			$ 345,000,000
Preferred stock, stated value per share	$ 50
Preferred stock, annual dividend rate (as a percent)	5.125%
Series M Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	9,000,000			9,000,000
Preferred stock issued, amount	$ 460,000,000			$ 460,000,000
Preferred stock, shares outstanding	9,000,000			9,000,000
Preferred stock outstanding, amount	$ 460,000,000			$ 460,000,000
Preferred stock, stated value per share	$ 50
Preferred stock, annual dividend rate (as a percent)	4.75%
Series N Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	5,000,000			5,000,000
Preferred stock issued, amount	$ 225,000,000			$ 225,000,000
Preferred stock, shares outstanding	5,000,000			5,000,000
Preferred stock outstanding, amount	$ 225,000,000			$ 225,000,000
Preferred stock, stated value per share	$ 50
Preferred stock, annual dividend rate (as a percent)	5.50%
Series O Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	50,000,000			50,000,000
Preferred stock issued, amount	$ 2,500,000,000			$ 2,500,000,000
Preferred stock, shares outstanding	50,000,000			50,000,000
Preferred stock outstanding, amount	$ 2,500,000,000			$ 2,500,000,000
Preferred stock, stated value per share	$ 50
Preferred stock, annual dividend rate (as a percent)	7.00%
Convertible Series 2004-1 Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	24,922			24,922
Preferred stock issued, amount	$ 2,492,000,000			$ 2,492,000,000
Preferred stock, shares outstanding	24,922			24,922
Preferred stock outstanding, amount	$ 2,492,000,000			$ 2,492,000,000
Preferred stock, stated value per share	$ 100,000
Preferred stock, annual dividend rate (as a percent)	5.375%
Series P Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	40,000,000			40,000,000
Preferred stock issued, amount	$ 1,000,000,000			$ 1,000,000,000
Preferred stock, shares outstanding	40,000,000			40,000,000
Preferred stock outstanding, amount	$ 1,000,000,000			$ 1,000,000,000
Preferred stock, stated value per share	$ 25
Preferred stock, annual dividend rate (as a percent)	4.50%
Series Q Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	15,000,000			15,000,000
Preferred stock issued, amount	$ 375,000,000			$ 375,000,000
Preferred stock, shares outstanding	15,000,000			15,000,000
Preferred stock outstanding, amount	$ 375,000,000			$ 375,000,000
Preferred stock, stated value per share	$ 25
Preferred stock, annual dividend rate (as a percent)	6.75%
Series R Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	21,000,000			21,000,000								1,200,000	20,000,000
Preferred stock issued, amount	$ 530,000,000			$ 530,000,000								$ 30,000,000	$ 500,000,000
Preferred stock, shares outstanding	21,000,000			21,000,000
Preferred stock outstanding, amount	$ 530,000,000			$ 530,000,000
Preferred stock, stated value per share	$ 25
Preferred stock, annual dividend rate (as a percent)	7.625%
Series S Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	280,000,000			280,000,000
Preferred stock issued, amount	$ 7,000,000,000			$ 7,000,000,000
Preferred stock, shares outstanding	280,000,000			280,000,000
Preferred stock outstanding, amount	$ 7,000,000,000			$ 7,000,000,000
Preferred stock, stated value per share	$ 25
Preferred stock, annual dividend rate (as a percent)	7.75%
Preferred Stock, Redemption Terms	P5Y
Series T Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	89,000,000			89,000,000					1,000,000	8,000,000	80,000,000
Preferred stock issued, amount	$ 2,225,000,000			$ 2,225,000,000					$ 25,000,000	$ 200,000,000	$ 2,000,000,000
Preferred stock, shares outstanding	89,000,000			89,000,000
Preferred stock outstanding, amount	$ 2,225,000,000			$ 2,225,000,000
Preferred stock, stated value per share	$ 25
Preferred stock, annual dividend rate (as a percent)	8.25%
Maximum [Member] | Series F Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, annual dividend rate (as a percent)	11.00%
Maximum [Member] | Series G Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, annual dividend rate (as a percent)	11.00%
Minimum [Member] | Series O Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, annual dividend rate (as a percent)	7.00%
Minimum [Member] | Series P Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, annual dividend rate (as a percent)	4.50%
Minimum [Member] | Series S Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, annual dividend rate (as a percent)	7.75%
Two-year Constant Maturity U.S. Treasury Rate [Member] | Series F Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividend rate, basis spread on variable rate	0.16%
Two-year Constant Maturity U.S. Treasury Rate [Member] | Series G Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividend rate, basis spread on variable rate	0.18%
Ten-year Constant Maturity U.S. Treasury Rate [Member] | Series O Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividend rate, basis spread on variable rate	2.375%
Three-Month LIBOR [Member] | Series P Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividend rate, basis spread on variable rate	0.75%
Three-Month LIBOR [Member] | Series S Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividend rate, basis spread on variable rate	4.23%
US Treasury [Member]
Class of Stock [Line Items]
Capital reserve amount for the fiscal year based on the amended Senior Preferred Stock Purchase agreement	$ 600,000,000	$ 0	$ 600,000,000	1,200,000,000		$ 3,000,000,000
Reduction in Dividends Paid	2,400,000,000
Annual Reduction of Capital Reserve Amount from 2013 to 2017, Senior Preferred Stock Purchase Agreement, Amendment	$ 600,000,000			$ 600,000,000	$ 600,000,000		$ 600,000,000
US Treasury [Member] | Scenario, Forecast [Member]
Class of Stock [Line Items]
Capital Reserve Amount, Fiscal Year, Senior Preferred Stock Purchase Agreement, December 2017 Amendment		$ 3,000,000,000

Equity (Deficit) Accumulated Ot

Equity (Deficit) Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity [Abstract]
Net unrealized gains on AFS securities for which we have not recorded OTTI	$ 87	$ 135	$ 455
Net unrealized gains on AFS securities for which we have recorded OTTI	423	581	903
Other	43	43	49
Accumulated other comprehensive income	$ 553	$ 759	$ 1,407

Equity (Deficit) Changes in AOC

Equity (Deficit) Changes in AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Total other comprehensive loss	$ 206	$ 648	$ 326
Accumulated Net Unrealized Investment Gain (Loss), AFS Securities [Member]
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	716	1,358
Other comprehensive income (loss) before reclassifications	53	(55)
Amounts reclassified from other comprehensive income	(259)	(587)
Total other comprehensive loss	(206)	(642)
Ending balance	510	716	1,358
Accumulated Other Comprehensive Income (Loss), Other [Member]
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	43	49
Other comprehensive income (loss) before reclassifications	8	2
Amounts reclassified from other comprehensive income	(8)	(8)
Total other comprehensive loss	0	(6)
Ending balance	43	43	49
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	759	1,407
Other comprehensive income (loss) before reclassifications	61	(53)
Amounts reclassified from other comprehensive income	(267)	(595)
Total other comprehensive loss	(206)	(648)
Ending balance	$ 553	$ 759	$ 1,407

Regulatory Capital Requiremen98

Regulatory Capital Requirements (Details) - USD ($) $ in Millions	Jan. 01, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Regulatory Capital Requirements [Abstract]
Component of statutory minimum capital requirement, percentage of the unpaid principal balance of outstanding Fannie Mae MBS held by third parties		0.45%		0.45%
Component of critical capital requirement, percentage of the unpaid principal balance of outstanding Fannie Mae MBS held by third parties		0.25%		0.25%
Net worth (deficit)		$ (3,686)	$ 3,600	$ 6,071	$ 4,059	$ 3,720
Core capital		(121,389)		(111,836)
Statutory minimum capital requirement		23,007		24,351
Deficit of core capital over statutory minimum capital requirement		$ (144,396)		$ (136,187)
Component of statutory minimum capital requirement, percentage of on-balance sheet assets, except those underlying Fannie Mae MBS held by third parties		2.50%		2.50%
Component of statutory minimum capital requirement, maximum percentage of other off-balance sheet obligations		0.45%		0.45%
Component of critical capital requirement, percentage of on-balance sheet assets, except those underlying Fannie Mae MBS held by third parties		1.25%		1.25%
Component of critical capital requirement, percentage of other off-balance sheet obligations		0.25%		0.25%
US Treasury [Member] | Scenario, Forecast [Member]
Related Parties [Line Items]
Capital Reserve Amount, Fiscal Year, Senior Preferred Stock Purchase Agreement, Amendment	$ 3,000

Concentrations of Credit Risk G

Concentrations of Credit Risk Geographic Concentration (Details) - Guaranty Book of Business [Member]	Dec. 31, 2017	Dec. 31, 2016
Single-Family [Member] | Conventional Mortgage [Member]
Concentration Risk [Line Items]
Percentage of book of business	100.00%	100.00%
Percentage of loans with detailed loan level information	99.00%	99.00%
Single-Family [Member] | Conventional Mortgage [Member] | Minimum [Member]
Concentration Risk [Line Items]
Percentage of loans with detailed loan level information	99.00%	99.00%
Single-Family [Member] | Conventional Mortgage [Member] | Midwest [Member]
Concentration Risk [Line Items]
Percentage of book of business	15.00%	15.00%
Single-Family [Member] | Conventional Mortgage [Member] | Northeast [Member]
Concentration Risk [Line Items]
Percentage of book of business	18.00%	18.00%
Single-Family [Member] | Conventional Mortgage [Member] | Southeast [Member]
Concentration Risk [Line Items]
Percentage of book of business	22.00%	22.00%
Single-Family [Member] | Conventional Mortgage [Member] | Southwest [Member]
Concentration Risk [Line Items]
Percentage of book of business	17.00%	17.00%
Single-Family [Member] | Conventional Mortgage [Member] | West [Member]
Concentration Risk [Line Items]
Percentage of book of business	28.00%	28.00%
Multifamily [Member]
Concentration Risk [Line Items]
Percentage of book of business	100.00%	100.00%
Percentage of loans with detailed loan level information	99.00%	99.00%
Multifamily [Member] | Midwest [Member]
Concentration Risk [Line Items]
Percentage of book of business	9.00%	9.00%
Multifamily [Member] | Northeast [Member]
Concentration Risk [Line Items]
Percentage of book of business	15.00%	16.00%
Multifamily [Member] | Southeast [Member]
Concentration Risk [Line Items]
Percentage of book of business	26.00%	25.00%
Multifamily [Member] | Southwest [Member]
Concentration Risk [Line Items]
Percentage of book of business	23.00%	22.00%
Multifamily [Member] | West [Member]
Concentration Risk [Line Items]
Percentage of book of business	27.00%	28.00%

Concentrations of Credit Risk S

Concentrations of Credit Risk SF Risk Characteristics (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Single-Family [Member] | Guaranty Book of Business [Member] | Conventional Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 days delinquent (percentage of book of business)	1.42%	1.30%
60 days delinquent (percentage of book of business)	0.43%	0.36%
Seriously delinquent (percentage of book of business)	1.15%	1.18%
30 days delinquent (percentage of conventional loans)	1.63%	1.51%
60 days delinquent (percentage of conventional loans)	0.50%	0.41%
Seriously delinquent (percentage of conventional loans)	1.24%	1.20%
Percentage of book of business	100.00%	100.00%
Percentage of loans with detailed loan level information	99.00%	99.00%
Single-Family [Member] | Guaranty Book of Business [Member] | Conventional Mortgage [Member] | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Seriously delinquent (percentage of conventional loans)	0.42%	0.50%
Percentage of book of business	19.00%	19.00%
Single-Family [Member] | Guaranty Book of Business [Member] | Conventional Mortgage [Member] | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Seriously delinquent (percentage of conventional loans)	3.71%	1.89%
Percentage of book of business	6.00%	6.00%
Single-Family [Member] | Guaranty Book of Business [Member] | Conventional Mortgage [Member] | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Seriously delinquent (percentage of conventional loans)	2.15%	3.07%
Percentage of book of business	4.00%	4.00%
Single-Family [Member] | Guaranty Book of Business [Member] | Conventional Mortgage [Member] | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Seriously delinquent (percentage of conventional loans)	2.02%	2.65%
Percentage of book of business	5.00%	5.00%
Single-Family [Member] | Guaranty Book of Business [Member] | Conventional Mortgage [Member] | All other states
Accounts, Notes, Loans and Financing Receivable [Line Items]
Seriously delinquent (percentage of conventional loans)	1.09%	1.11%
Percentage of book of business	66.00%	66.00%
Single-Family [Member] | Guaranty Book of Business [Member] | Conventional Mortgage [Member] | Estimated mark-to-market LTV ratio greater than 100% [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Seriously delinquent (percentage of conventional loans)	11.70%	10.44%
Percentage of book of business	1.00%	2.00%
Single-Family [Member] | Guaranty Book of Business [Member] | Conventional Mortgage [Member] | Alt-A [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Seriously delinquent (percentage of conventional loans)	4.95%	5.00%
Percentage of book of business	2.00%	3.00%
Single-Family [Member] | Guaranty Book of Business [Member] | Conventional Mortgage [Member] | 2004 and Prior
Accounts, Notes, Loans and Financing Receivable [Line Items]
Seriously delinquent (percentage of conventional loans)	3.28%	2.82%
Percentage of book of business	4.00%	5.00%
Single-Family [Member] | Guaranty Book of Business [Member] | Conventional Mortgage [Member] | 2005 - 2008
Accounts, Notes, Loans and Financing Receivable [Line Items]
Seriously delinquent (percentage of conventional loans)	6.55%	6.39%
Percentage of book of business	6.00%	8.00%
Single-Family [Member] | Guaranty Book of Business [Member] | Conventional Mortgage [Member] | 2009 - 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Seriously delinquent (percentage of conventional loans)	0.53%	0.36%
Percentage of book of business	90.00%	87.00%
Single-Family [Member] | Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Serious delinquency: days past due	90 days	90 days
Single-Family [Member] | Minimum [Member] | Guaranty Book of Business [Member] | Conventional Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of loans with detailed loan level information	99.00%	99.00%
Multifamily [Member] | Guaranty Book of Business [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 days delinquent (percentage of book of business)	0.03%	0.02%
Seriously delinquent (percentage of book of business)	0.11%	0.05%
Percentage of book of business	100.00%	100.00%
Percentage of loans with detailed loan level information	99.00%	99.00%
Multifamily [Member] | Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Serious delinquency: days past due	60 days	60 days
Multifamily [Member] | Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Serious delinquency: days past due	89 days	89 days
Current debt service coverage ratio	1	1

Concentrations of Credit Risk M

Concentrations of Credit Risk MF Risk Characteristics (Details) - Multifamily [Member]	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Serious delinquency: days past due	60 days	60 days
Current debt service coverage ratio reporting lag	3 months	3 months
Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current debt service coverage ratio	1	1
Serious delinquency: days past due	89 days	89 days
Current debt service coverage ratio reporting lag	6 months	6 months
Guaranty Book of Business [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 days delinquent (percentage of book of business)	0.03%	0.02%
Seriously delinquent (percentage of book of business)	0.11%	0.05%
Percentage of book of business	100.00%	100.00%
Percentage of loans with detailed loan level information	99.00%	99.00%
Guaranty Book of Business [Member] | Original LTV ratio greater than 80% [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of book of business	2.00%	2.00%
Loans seriously delinquent, percentage by unpaid principal balance	0.21%	0.22%
Guaranty Book of Business [Member] | Original LTV ratio less than or equal to 80% [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of book of business	98.00%	98.00%
Loans seriously delinquent, percentage by unpaid principal balance	0.11%	0.05%
Guaranty Book of Business [Member] | Current DSCR less than 100% [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of book of business	2.00%	2.00%
Loans seriously delinquent, percentage by unpaid principal balance	1.96%	1.96%

Concentrations of Credit Risk O

Concentrations of Credit Risk Other Concentrations (Details) $ in Millions	Dec. 31, 2017USD ($)servicerscounterpartiesinsurers	Dec. 31, 2016USD ($)servicerscounterpartiesinsurers
Concentration Risk [Line Items]
Estimated benefit included in combined loss reserves	$ 989	$ 1,400
Receivable from claims on insured, defaulted loans excluding government insured loans	858	1,000
Allowance for mortgage insurance receivable	593	638
Unpaid principal balance of guaranteed non-agency securities in our portfolio	$ 849	1,400
PMI [Member]
Concentration Risk [Line Items]
Mortgage insurance coverage risk in force percentage to be paid in cash	71.50%
Mortgage insurance coverage risk in force percentage to be deferred	28.50%
Triad [Member]
Concentration Risk [Line Items]
Mortgage insurance coverage risk in force percentage to be paid in cash	75.00%
Mortgage insurance coverage risk in force percentage to be deferred	25.00%
Mortgage Sellers and Servicers [Member]
Concentration Risk [Line Items]
Receivable from claims on insured, defaulted loans excluding government insured loans	$ 75	141
Ambac Assurance Corporation [Member]
Concentration Risk [Line Items]
Mortgage insurance coverage risk in force percentage to be paid in cash	45.00%
Other agency [Member]
Concentration Risk [Line Items]
Guaranteed securities issued by Freddie Mac, the federal government and its agencies	$ 9,500	$ 11,600
Non-Government Guarantee [Member] | Insurance Service Provider Concentration Risk [Member] | Ambac Assurance Corporation [Member]
Concentration Risk [Line Items]
Percentage of concentration risk	36.00%
Unpaid principal balance of guaranteed non-agency securities in our portfolio	$ 308
Single-Family [Member]
Concentration Risk [Line Items]
Number of mortgage insurance companies who provided majority of mortgage insurance coverage risk in force | insurers	3	3
Number of mortgage insurers publicly disclosed credit quality deterioration | insurers	3
Single-Family [Member] | Guaranty Book of Business [Member]
Concentration Risk [Line Items]
Mortgage insurance coverage risk in force	$ 138,500	$ 126,200
Mortgage insurance coverage risk in force as a percentage of book of business	5.00%	4.00%
Primary mortgage insurance coverage risk in force	$ 137,900	$ 125,600
Pool mortgage insurance coverage risk in force	$ 519	$ 617
Single-Family [Member] | Guaranty Book of Business [Member] | Conventional Mortgage [Member]
Concentration Risk [Line Items]
Percentage of book of business	100.00%	100.00%
Single-Family [Member] | Guaranty Book of Business [Member] | Insurance Service Provider Concentration Risk [Member]
Concentration Risk [Line Items]
Mortgage insurance coverage risk in force for insurers with credit quality deterioration	$ 6,100
Percentage of concentration risk	4.00%
Single-Family [Member] | Guaranty Book of Business [Member] | Insurance Service Provider Concentration Risk [Member] | Group of Top Mortgage Insurance Companies [Member]
Concentration Risk [Line Items]
Percentage of concentration risk	65.00%	66.00%
Single-Family [Member] | Depository Servicer [Member]
Concentration Risk [Line Items]
Number of mortgage servicers, including their affiliates, which serviced the majority of our guaranty book of business | servicers	5	5
Single-Family [Member] | Depository Servicer [Member] | Guaranty Book of Business [Member] | Credit Concentration Risk [Member] | Group of Largest Mortgage Servicers including Affiliates [Member]
Concentration Risk [Line Items]
Percentage of concentration risk	35.00%	36.00%
Single-Family [Member] | Non-Depository Servicer [Member]
Concentration Risk [Line Items]
Number of mortgage servicers, including their affiliates, which serviced the majority of our guaranty book of business | servicers	5	5
Single-Family [Member] | Non-Depository Servicer [Member] | Guaranty Book of Business [Member] | Credit Concentration Risk [Member] | Group of Largest Mortgage Servicers including Affiliates [Member]
Concentration Risk [Line Items]
Percentage of concentration risk	20.00%	16.00%
Multifamily [Member]
Concentration Risk [Line Items]
Number of mortgage servicers, including their affiliates, which serviced the majority of our guaranty book of business | servicers	5	5
Maximum potential loss recovery from lenders under risk sharing agreements	$ 63,400	$ 54,800
Multifamily [Member] | Lender Concentration Risk [Member]
Concentration Risk [Line Items]
Number of DUS lenders | counterparties	4	4
Multifamily [Member] | Lender Concentration Risk [Member] | Four Major Lenders [Member]
Concentration Risk [Line Items]
Percentage of concentration risk	43.00%	43.00%
Multifamily [Member] | Guaranty Book of Business [Member]
Concentration Risk [Line Items]
Percentage of book of business	100.00%	100.00%
Multifamily [Member] | Guaranty Book of Business [Member] | Credit Concentration Risk [Member] | Group of Largest Mortgage Servicers including Affiliates [Member]
Concentration Risk [Line Items]
Percentage of concentration risk	48.00%	47.00%

Netting Arrangements (Details)

Netting Arrangements (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets:
Derivative assets, gross amount	$ 4,422	$ 5,168
Derivative asset, gross amount offset	(4,272)	(4,514)
Derivative assets, net amount presented in our consolidated balance sheets	150	654
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	(117)	(357)
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	(1)	(22)
Derivative assets, net amount	32	275
Securities purchased under agreements to resell, or similar arrangements, gross amount	44,670	51,115
Securities purchased under agreements to resell or similar arrangements, gross amount offset	0	0
Securities purchased under agreements to resell or similar arrangements, net amount presented in our consolidated balance sheets	44,670	51,115
Securities purchased under agreements to resell, under master netting arrangement, amounts not offset in our consolidated balance sheets, financial instruments	0	0
Securities purchased under agreements to resell or similar arrangements, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	(44,670)	(51,115)
Securities purchased under agreements to resell or similar arrangements, net amount	0	0
Total assets, gross amount	49,092	56,283
Total assets, gross amount offset	(4,272)	(4,514)
Total assets, net amount presented in the consolidated balance sheets	44,820	51,769
Total assets, under the master netting arrangements, not offset in our consolidated balance sheets, financial instruments	(117)	(357)
Total assets, under master netting arrangements, not offset in our consolidated balance sheets, collateral	(44,671)	(51,137)
Total assets, net amount	32	275
Liabilities:
Derivative liabilities, gross amount	(5,306)	(8,057)
Derivative liabilities, gross amount offset	4,979	6,844
Derivative liabilities, net amount presented in our consolidated balance sheets	(327)	(1,213)
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	117	357
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	104	107
Derivative liabilities, net amount	(106)	(749)
Total liabilities, gross amount	(5,306)	(8,057)
Total liabilities, gross amount offset	4,979	6,844
Total liabilities, net amount presented in our consolidated balance sheets	(327)	(1,213)
Total liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial statements	117	357
Total liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	104	107
Total liabilities, net amount	(106)	(749)
Risk management derivatives
Assets:
Derivative asset, gross amount offset	(4,272)	(4,514)
Liabilities:
Derivative liabilities, gross amount offset	4,979	6,844
Mortgage commitment derivatives
Assets:
Derivative assets, gross amount	132	631
Derivative asset, gross amount offset	0	0
Derivative assets, net amount presented in our consolidated balance sheets	132	631
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	(117)	(357)
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	(1)	(22)
Derivative assets, net amount	14	252
Liabilities:
Derivative liabilities, gross amount	(228)	(737)
Derivative liabilities, gross amount offset	0	0
Derivative liabilities, net amount presented in our consolidated balance sheets	(228)	(737)
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	117	357
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	93	16
Derivative liabilities, net amount	(18)	(364)
Over the Counter [Member] | Risk management derivatives
Assets:
Derivative assets, gross amount	2,479	3,688
Derivative asset, gross amount offset	(2,464)	(3,667)
Derivative assets, net amount presented in our consolidated balance sheets	15	21
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	0	0
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	0	0
Derivative assets, net amount	15	21
Liabilities:
Derivative liabilities, gross amount	(3,045)	(4,905)
Derivative liabilities, gross amount offset	2,957	4,520
Derivative liabilities, net amount presented in our consolidated balance sheets	(88)	(385)
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	0	0
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	0	0
Derivative liabilities, net amount	(88)	(385)
Exchange Cleared [Member] | Risk management derivatives
Assets:
Derivative assets, gross amount	1,811	849
Derivative asset, gross amount offset	(1,808)	(847)
Derivative assets, net amount presented in our consolidated balance sheets	3	2
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	0	0
Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	0	0
Derivative assets, net amount	3	2
Liabilities:
Derivative liabilities, gross amount	(2,033)	(2,415)
Derivative liabilities, gross amount offset	2,022	2,324
Derivative liabilities, net amount presented in our consolidated balance sheets	(11)	(91)
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments	0	0
Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral	11	91
Derivative liabilities, net amount	$ 0	$ 0

Netting Arrangements Narratives

Netting Arrangements Narratives (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Fair value of non-cash collateral we pledged	$ 747,000,000	$ 1,300,000,000
Fair value of non-cash collateral received	44,700,000,000	51,200,000,000
Fair value of non-cash collateral received that could be sold or repledged	42,500,000,000	45,500,000,000
Fair value of underlying collateral that was sold or repledged	0	0
Derivative assets not subject to an enforceable master netting arrangement	21,000,000	33,000,000
Derivative liabilities not subject to an enforceable master netting arrangement	1,000,000	2,000,000
Cash and cash equivalents [Member]
Derivative [Line Items]
Securities purchased under agreements to resell	$ 25,200,000,000	$ 20,700,000,000

Fair Value Levels Hierarchy (De

Fair Value Levels Hierarchy (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets [Abstract]
Mortgage loans held for investment, at fair value	$ 10,596	$ 12,057
Other assets [Abstract]
Derivative asset, gross amount offset	(4,272)	(4,514)
Other liabilities [Abstract]
Derivative liabilities, gross amount offset	(4,979)	(6,844)
Mortgage commitment derivatives
Other assets [Abstract]
Derivative asset, gross amount offset	0	0
Other liabilities [Abstract]
Derivative liabilities, gross amount offset	0	0
Fannie Mae [Member]
Liabilities [Abstract]
Long-term debt, fair value	8,186	9,582
Consolidated Trusts [Member]
Liabilities [Abstract]
Long-term debt, fair value	30,493	36,524
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets [Abstract]
Trading securities	29,222	32,317
Available-for-sale securities	0	0
Mortgage loans held for investment, at fair value	0	0
Other assets [Abstract]
Derivatives assets at fair value	0	0
Total assets at fair value	64,282	73,794
Other liabilities [Abstract]
Derivatives liabilities at fair value	0	0
Total liabilities at fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fannie Mae [Member]
Liabilities [Abstract]
Long-term debt, fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Consolidated Trusts [Member]
Liabilities [Abstract]
Long-term debt, fair value	0	0
Significant Other Observable Inputs (Level 2) [Member]
Assets [Abstract]
Trading securities	4,256	7,118
Available-for-sale securities	3,530	6,210
Mortgage loans held for investment, at fair value	2,886,470	2,767,813
Other assets [Abstract]
Derivatives assets at fair value	4,274	5,019
Total assets at fair value	2,948,237	2,844,940
Other liabilities [Abstract]
Derivatives liabilities at fair value	5,272	7,921
Total liabilities at fair value	3,302,681	3,243,215
Significant Other Observable Inputs (Level 2) [Member] | Fannie Mae [Member]
Liabilities [Abstract]
Long-term debt, fair value	249,780	298,980
Significant Other Observable Inputs (Level 2) [Member] | Consolidated Trusts [Member]
Liabilities [Abstract]
Long-term debt, fair value	3,014,250	2,901,316
Significant Unobservable Inputs (Level 3) [Member]
Assets [Abstract]
Trading securities	1,201	1,127
Available-for-sale securities	1,313	2,153
Mortgage loans held for investment, at fair value	315,719	316,742
Other assets [Abstract]
Derivatives assets at fair value	169	182
Total assets at fair value	324,173	323,739
Other liabilities [Abstract]
Derivatives liabilities at fair value	35	138
Total liabilities at fair value	42,389	38,870
Significant Unobservable Inputs (Level 3) [Member] | Fannie Mae [Member]
Liabilities [Abstract]
Long-term debt, fair value	837	770
Significant Unobservable Inputs (Level 3) [Member] | Consolidated Trusts [Member]
Liabilities [Abstract]
Long-term debt, fair value	40,683	36,668
Recurring Fair Value Measurements [Member]
Assets [Abstract]
Trading securities	34,679	40,562
Available-for-sale securities	4,843	8,363
Mortgage loans held for investment, at fair value	10,596	12,057
Other assets [Abstract]
Derivatives assets at fair value	171	687
Derivative asset, gross amount offset	(4,272)	(4,514)
Total assets at fair value	50,289	61,669
Liabilities [Abstract]
Long-term debt, fair value	38,679	46,106
Other liabilities [Abstract]
Derivatives liabilities at fair value	328	1,215
Derivative liabilities, gross amount offset	(4,979)	(6,844)
Total liabilities at fair value	39,007	47,321
Recurring Fair Value Measurements [Member] | Swaps [Member]
Other assets [Abstract]
Derivatives assets at fair value	4,181	4,296
Other liabilities [Abstract]
Derivatives liabilities at fair value	4,754	6,981
Recurring Fair Value Measurements [Member] | Swaptions [Member]
Other assets [Abstract]
Derivatives assets at fair value	108	241
Other liabilities [Abstract]
Derivatives liabilities at fair value	324	339
Recurring Fair Value Measurements [Member] | Other
Other assets [Abstract]
Derivatives assets at fair value	22	33
Other liabilities [Abstract]
Derivatives liabilities at fair value	1	2
Recurring Fair Value Measurements [Member] | Mortgage commitment derivatives
Other assets [Abstract]
Derivatives assets at fair value	132	631
Other liabilities [Abstract]
Derivatives liabilities at fair value	228	737
Recurring Fair Value Measurements [Member] | Fannie Mae [Member]
Liabilities [Abstract]
Long-term debt, fair value	8,186	9,582
Recurring Fair Value Measurements [Member] | Fannie Mae [Member] | Senior floating [Member]
Liabilities [Abstract]
Long-term debt, fair value	8,186	9,582
Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member]
Liabilities [Abstract]
Long-term debt, fair value	30,493	36,524
Recurring Fair Value Measurements [Member] | Fannie Mae [Member]
Assets [Abstract]
Trading securities	3,876	4,769
Available-for-sale securities	2,119	2,554
Recurring Fair Value Measurements [Member] | Other agency [Member]
Assets [Abstract]
Trading securities	1,118	2,058
Available-for-sale securities	357	547
Recurring Fair Value Measurements [Member] | Alt-A and subprime private-label securities [Member]
Assets [Abstract]
Trading securities	453	636
Available-for-sale securities	1,314	2,709
Recurring Fair Value Measurements [Member] | CMBS [Member]
Assets [Abstract]
Trading securities	9	761
Available-for-sale securities	15	819
Recurring Fair Value Measurements [Member] | Mortgage revenue bonds [Member]
Assets [Abstract]
Trading securities	1	21
Available-for-sale securities	671	1,272
Recurring Fair Value Measurements [Member] | Other [Member]
Assets [Abstract]
Available-for-sale securities	367	462
Recurring Fair Value Measurements [Member] | U.S. Treasury Securities [Member]
Assets [Abstract]
Trading securities	29,222	32,317
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets [Abstract]
Trading securities	29,222	32,317
Available-for-sale securities	0	0
Mortgage loans held for investment, at fair value	0	0
Other assets [Abstract]
Derivatives assets at fair value	0	0
Total assets at fair value	29,222	32,317
Liabilities [Abstract]
Long-term debt, fair value	0	0
Other liabilities [Abstract]
Derivatives liabilities at fair value	0	0
Total liabilities at fair value	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Swaps [Member]
Other assets [Abstract]
Derivatives assets at fair value	0	0
Other liabilities [Abstract]
Derivatives liabilities at fair value	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Swaptions [Member]
Other assets [Abstract]
Derivatives assets at fair value	0	0
Other liabilities [Abstract]
Derivatives liabilities at fair value	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other
Other assets [Abstract]
Derivatives assets at fair value	0	0
Other liabilities [Abstract]
Derivatives liabilities at fair value	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Mortgage commitment derivatives
Other assets [Abstract]
Derivatives assets at fair value	0	0
Other liabilities [Abstract]
Derivatives liabilities at fair value	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fannie Mae [Member]
Liabilities [Abstract]
Long-term debt, fair value	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fannie Mae [Member] | Senior floating [Member]
Liabilities [Abstract]
Long-term debt, fair value	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Consolidated Trusts [Member]
Liabilities [Abstract]
Long-term debt, fair value	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fannie Mae [Member]
Assets [Abstract]
Trading securities	0	0
Available-for-sale securities	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other agency [Member]
Assets [Abstract]
Trading securities	0	0
Available-for-sale securities	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Alt-A and subprime private-label securities [Member]
Assets [Abstract]
Trading securities	0	0
Available-for-sale securities	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | CMBS [Member]
Assets [Abstract]
Trading securities	0	0
Available-for-sale securities	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Mortgage revenue bonds [Member]
Assets [Abstract]
Trading securities	0	0
Available-for-sale securities	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other [Member]
Assets [Abstract]
Available-for-sale securities	0	0
Recurring Fair Value Measurements [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury Securities [Member]
Assets [Abstract]
Trading securities	29,222	32,317
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets [Abstract]
Trading securities	4,256	7,118
Available-for-sale securities	3,530	6,210
Mortgage loans held for investment, at fair value	9,480	10,860
Other assets [Abstract]
Derivatives assets at fair value	4,274	5,019
Total assets at fair value	21,540	29,207
Liabilities [Abstract]
Long-term debt, fair value	37,721	45,518
Other liabilities [Abstract]
Derivatives liabilities at fair value	5,272	7,921
Total liabilities at fair value	42,993	53,439
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Swaps [Member]
Other assets [Abstract]
Derivatives assets at fair value	4,035	4,159
Other liabilities [Abstract]
Derivatives liabilities at fair value	4,721	6,933
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Swaptions [Member]
Other assets [Abstract]
Derivatives assets at fair value	108	241
Other liabilities [Abstract]
Derivatives liabilities at fair value	324	339
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Other
Other assets [Abstract]
Derivatives assets at fair value	0	0
Other liabilities [Abstract]
Derivatives liabilities at fair value	0	0
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Mortgage commitment derivatives
Other assets [Abstract]
Derivatives assets at fair value	131	619
Other liabilities [Abstract]
Derivatives liabilities at fair value	227	649
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fannie Mae [Member]
Liabilities [Abstract]
Long-term debt, fair value	7,810	9,235
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fannie Mae [Member] | Senior floating [Member]
Liabilities [Abstract]
Long-term debt, fair value	7,810	9,235
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Consolidated Trusts [Member]
Liabilities [Abstract]
Long-term debt, fair value	29,911	36,283
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fannie Mae [Member]
Assets [Abstract]
Trading securities	2,905	3,934
Available-for-sale securities	1,911	2,324
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Other agency [Member]
Assets [Abstract]
Trading securities	1,083	2,058
Available-for-sale securities	357	542
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Alt-A and subprime private-label securities [Member]
Assets [Abstract]
Trading securities	259	365
Available-for-sale securities	1,237	2,492
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | CMBS [Member]
Assets [Abstract]
Trading securities	9	761
Available-for-sale securities	15	819
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Mortgage revenue bonds [Member]
Assets [Abstract]
Trading securities	0	0
Available-for-sale securities	0	0
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | Other [Member]
Assets [Abstract]
Available-for-sale securities	10	33
Recurring Fair Value Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. Treasury Securities [Member]
Assets [Abstract]
Trading securities	0	0
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets [Abstract]
Trading securities	1,201	1,127
Available-for-sale securities	1,313	2,153
Mortgage loans held for investment, at fair value	1,116	1,197
Other assets [Abstract]
Derivatives assets at fair value	169	182
Total assets at fair value	3,799	4,659
Liabilities [Abstract]
Long-term debt, fair value	958	588
Other liabilities [Abstract]
Derivatives liabilities at fair value	35	138
Total liabilities at fair value	993	726
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Swaps [Member]
Other assets [Abstract]
Derivatives assets at fair value	146	137
Other liabilities [Abstract]
Derivatives liabilities at fair value	33	48
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Swaptions [Member]
Other assets [Abstract]
Derivatives assets at fair value	0	0
Other liabilities [Abstract]
Derivatives liabilities at fair value	0	0
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other
Other assets [Abstract]
Derivatives assets at fair value	22	33
Other liabilities [Abstract]
Derivatives liabilities at fair value	1	2
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Mortgage commitment derivatives
Other assets [Abstract]
Derivatives assets at fair value	1	12
Other liabilities [Abstract]
Derivatives liabilities at fair value	1	88
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fannie Mae [Member]
Liabilities [Abstract]
Long-term debt, fair value	376	347
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fannie Mae [Member] | Senior floating [Member]
Liabilities [Abstract]
Long-term debt, fair value	376	347
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Consolidated Trusts [Member]
Liabilities [Abstract]
Long-term debt, fair value	582	241
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fannie Mae [Member]
Assets [Abstract]
Trading securities	971	835
Available-for-sale securities	208	230
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other agency [Member]
Assets [Abstract]
Trading securities	35	0
Available-for-sale securities	0	5
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Alt-A and subprime private-label securities [Member]
Assets [Abstract]
Trading securities	194	271
Available-for-sale securities	77	217
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | CMBS [Member]
Assets [Abstract]
Trading securities	0	0
Available-for-sale securities	0	0
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Mortgage revenue bonds [Member]
Assets [Abstract]
Trading securities	1	21
Available-for-sale securities	671	1,272
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other [Member]
Assets [Abstract]
Available-for-sale securities	357	429
Recurring Fair Value Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] | U.S. Treasury Securities [Member]
Assets [Abstract]
Trading securities	$ 0	$ 0

Fair Value Level 3 Rollforward

Fair Value Level 3 Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Trading securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Unrealized Gains (Losses) included in net income related to assets still held	$ 11	$ (3)	$ (8)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,127	1,398	3,030
Total gains or (losses) (realized/unrealized) Included in Net Income	59	0	8
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)	0	0	0
Purchases	99	0	0
Sales	(81)	(679)	(1,200)
Issues	0	0	0
Settlements	(39)	(65)	(148)
Transfers out of Level 3	(991)	(388)	(322)
Transfers into Level 3	1,027	861	30
Ending Balance	1,201	1,127	1,398
Trading securities [Member] | Fannie Mae [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Unrealized Gains (Losses) included in net income related to assets still held	6	0	0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	835	0	305
Total gains or (losses) (realized/unrealized) Included in Net Income	41	0	(27)
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)	0	0	0
Purchases	64	0	0
Sales	0	0	(2)
Issues	0	0	0
Settlements	(5)	(1)	0
Transfers out of Level 3	(991)	(24)	(278)
Transfers into Level 3	1,027	860	2
Ending Balance	971	835	0
Trading securities [Member] | Other agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Unrealized Gains (Losses) included in net income related to assets still held	0	0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	0	0
Total gains or (losses) (realized/unrealized) Included in Net Income	0	0
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)	0	0
Purchases	35	0
Sales	0	0
Issues	0	0
Settlements	0	0
Transfers out of Level 3	0	(1)
Transfers into Level 3	0	1
Ending Balance	35	0	0
Trading securities [Member] | Alt-A and subprime private-label securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Unrealized Gains (Losses) included in net income related to assets still held	5	(1)	25
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	271	949	1,904
Total gains or (losses) (realized/unrealized) Included in Net Income	15	(33)	72
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)	0	0	0
Purchases	0	0	0
Sales	(60)	(231)	(878)
Issues	0	0	0
Settlements	(32)	(51)	(133)
Transfers out of Level 3	0	(363)	(44)
Transfers into Level 3	0	0	28
Ending Balance	194	271	949
Trading securities [Member] | Mortgage revenue bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Unrealized Gains (Losses) included in net income related to assets still held	0	(2)	(33)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	21	449	722
Total gains or (losses) (realized/unrealized) Included in Net Income	3	33	(41)
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)	0	0	0
Purchases	0	0	0
Sales	(21)	(448)	(220)
Issues	0	0	0
Settlements	(2)	(13)	(12)
Transfers out of Level 3	0	0	0
Transfers into Level 3	0	0	0
Ending Balance	1	21	449
Trading securities [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Unrealized Gains (Losses) included in net income related to assets still held			0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		0	99
Total gains or (losses) (realized/unrealized) Included in Net Income			4
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)			0
Purchases			0
Sales			(100)
Issues			0
Settlements			(3)
Transfers out of Level 3			0
Transfers into Level 3			0
Ending Balance			0
Available-for-sale securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Unrealized Gains (Losses) included in net income related to assets still held	0	0	0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2,153	8,431	15,080
Total gains or (losses) (realized/unrealized) Included in Net Income	99	316	839
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)	(76)	(279)	(661)
Purchases	0	0	421
Sales	(503)	(2,731)	(4,926)
Issues	0	0	0
Settlements	(342)	(692)	(2,132)
Transfers out of Level 3	(76)	(3,128)	(540)
Transfers into Level 3	58	236	350
Ending Balance	1,313	2,153	8,431
Available-for-sale securities [Member] | Fannie Mae [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Unrealized Gains (Losses) included in net income related to assets still held	0	0	0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	230	0	0
Total gains or (losses) (realized/unrealized) Included in Net Income	2	0	0
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)	(1)	0	0
Purchases	0	0	421
Sales	0	0	(425)
Issues	0	0	0
Settlements	(9)	0	(8)
Transfers out of Level 3	(72)	(1)	0
Transfers into Level 3	58	231	12
Ending Balance	208	230	0
Available-for-sale securities [Member] | Other agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Unrealized Gains (Losses) included in net income related to assets still held	0	0	0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	5	4	6
Total gains or (losses) (realized/unrealized) Included in Net Income	0	0	0
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)	0	0	0
Purchases	0	0	0
Sales	(1)	0	0
Issues	0	0	0
Settlements	0	0	(1)
Transfers out of Level 3	(4)	(4)	(2)
Transfers into Level 3	0	5	1
Ending Balance	0	5	4
Available-for-sale securities [Member] | Alt-A and subprime private-label securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Unrealized Gains (Losses) included in net income related to assets still held	0	0	0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	217	4,322	8,380
Total gains or (losses) (realized/unrealized) Included in Net Income	54	184	814
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)	(53)	(233)	(555)
Purchases	0	0	0
Sales	(105)	(997)	(3,079)
Issues	0	0	0
Settlements	(36)	(220)	(1,037)
Transfers out of Level 3	0	(2,839)	(538)
Transfers into Level 3	0	0	337
Ending Balance	77	217	4,322
Available-for-sale securities [Member] | Mortgage revenue bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Unrealized Gains (Losses) included in net income related to assets still held	0	0	0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,272	2,701	4,023
Total gains or (losses) (realized/unrealized) Included in Net Income	35	132	51
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)	(11)	(34)	(104)
Purchases	0	0	0
Sales	(392)	(1,129)	(410)
Issues	0	0	0
Settlements	(233)	(398)	(859)
Transfers out of Level 3	0	0	0
Transfers into Level 3	0	0	0
Ending Balance	671	1,272	2,701
Available-for-sale securities [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Unrealized Gains (Losses) included in net income related to assets still held	0	0	0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	429	1,404	2,671
Total gains or (losses) (realized/unrealized) Included in Net Income	8	0	(26)
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)	(11)	(12)	(2)
Purchases	0	0	0
Sales	(5)	(605)	(1,012)
Issues	0	0	0
Settlements	(64)	(74)	(227)
Transfers out of Level 3	0	(284)	0
Transfers into Level 3	0	0	0
Ending Balance	357	429	1,404
Mortgage loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Unrealized Gains (Losses) included in net income related to assets still held	25	17	(20)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,197	1,477	1,833
Total gains or (losses) (realized/unrealized) Included in Net Income	45	129	57
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)	0	0	0
Purchases	5	36	5
Sales	0	(392)	0
Issues	0	0	0
Settlements	(233)	(255)	(350)
Transfers out of Level 3	(70)	(77)	(377)
Transfers into Level 3	172	279	309
Ending Balance	1,116	1,197	1,477
Net derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Unrealized Gains (Losses) included in net income related to assets still held	13	(132)	(2)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	44	157	45
Total gains or (losses) (realized/unrealized) Included in Net Income	111	15	(55)
Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss)	0	0	0
Purchases	0	0	0
Sales	0	0	0
Issues	0	(8)	(4)
Settlements	(22)	(122)	169
Transfers out of Level 3	6	2	(7)
Transfers into Level 3	(5)	0	9
Ending Balance	134	44	157
Long-term debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net unrealized Gains (Losses) included in net income related to liabilities still held	(40)	13	11
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(588)	(865)	(890)
Total gains (losses) (realized/unrealized) Included in Net Income	(38)	(53)	(15)
Total gains (losses) Included in Other Comprehensive Income	0	0	0
Purchases	0	0	0
Sales	0	0	0
Issues	(2)	(74)	(66)
Settlements	66	378	57
Transfers out of Level 3	388	215	228
Transfers Into Level 3	(784)	(189)	(179)
Ending Balance	(958)	(588)	(865)
Long-term debt [Member] | Consolidated Trusts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net unrealized Gains (Losses) included in net income related to liabilities still held	(11)	(9)	17
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(241)	(496)	(527)
Total gains (losses) (realized/unrealized) Included in Net Income	(9)	(75)	(9)
Total gains (losses) Included in Other Comprehensive Income	0	0	0
Purchases	0	0	0
Sales	0	0	0
Issues	(2)	(74)	(66)
Settlements	66	378	57
Transfers out of Level 3	388	215	228
Transfers Into Level 3	(784)	(189)	(179)
Ending Balance	(582)	(241)	(496)
Long-term debt [Member] | Senior floating [Member] | Fannie Mae [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net unrealized Gains (Losses) included in net income related to liabilities still held	(29)	22	(6)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(347)	(369)	(363)
Total gains (losses) (realized/unrealized) Included in Net Income	(29)	22	(6)
Total gains (losses) Included in Other Comprehensive Income	0	0	0
Purchases	0	0	0
Sales	0	0	0
Issues	0	0	0
Settlements	0	0	0
Transfers out of Level 3	0	0	0
Transfers Into Level 3	0	0	0
Ending Balance	$ (376)	$ (347)	$ (369)

Fair Value Level 3 Valuation In

Fair Value Level 3 Valuation Inputs - Recurring (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	$ 10,596	$ 12,057
Net derivatives	150	654
Fannie Mae [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt	(8,186)	(9,582)
Consolidated Trusts [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt	(30,493)	(36,524)
Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	34,679	40,562
Available-for-sale securities	4,843	8,363
Mortgage loans held for investment, at fair value	10,596	12,057
Long-term debt	(38,679)	(46,106)
Recurring Fair Value Measurements [Member] | Alt-A and subprime private-label securities [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	453	636
Available-for-sale securities	1,314	2,709
Recurring Fair Value Measurements [Member] | Mortgage revenue bonds [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	1	21
Available-for-sale securities	671	1,272
Recurring Fair Value Measurements [Member] | Other [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	367	462
Recurring Fair Value Measurements [Member] | Fannie Mae [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt	(8,186)	(9,582)
Recurring Fair Value Measurements [Member] | Fannie Mae [Member] | Senior floating [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt	(8,186)	(9,582)
Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt	(30,493)	(36,524)
Significant Unobservable Inputs (Level 3) [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	1,201	1,127
Available-for-sale securities	1,313	2,153
Mortgage loans held for investment, at fair value	315,719	316,742
Significant Unobservable Inputs (Level 3) [Member] | Fannie Mae [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt	(837)	(770)
Significant Unobservable Inputs (Level 3) [Member] | Consolidated Trusts [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt	(40,683)	(36,668)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	1,201	1,127
Available-for-sale securities	1,313	2,153
Mortgage loans held for investment, at fair value	1,116	1,197
Net derivatives	134	44
Long-term debt	(958)	(588)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Agency [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	1,006	835
Available-for-sale securities	208	235
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Alt-A and subprime private-label securities [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	194	271
Available-for-sale securities	77	217
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Mortgage revenue bonds [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	1	21
Available-for-sale securities	671	1,272
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Other [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	357	429
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with inputs [Member] | Alt-A and subprime private-label securities [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities		$ 232
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with inputs [Member] | Alt-A and subprime private-label securities [Member] | Trading securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)		0.40%
Prepayment Speed (%)		4.30%
Severity (%)		71.00%
Spread (bps)		2.446%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with inputs [Member] | Alt-A and subprime private-label securities [Member] | Trading securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)		10.90%
Prepayment Speed (%)		7.40%
Severity (%)		95.00%
Spread (bps)		2.539%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with inputs [Member] | Alt-A and subprime private-label securities [Member] | Trading securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)		8.20%
Prepayment Speed (%)		6.60%
Severity (%)		88.90%
Spread (bps)		2.515%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with inputs [Member] | Other [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities		$ 47
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with inputs [Member] | Other [Member] | Available-for-sale securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)		0.50%
Prepayment Speed (%)		2.50%
Severity (%)		20.00%
Spread (bps)		2.216%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with inputs [Member] | Other [Member] | Available-for-sale securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)		3.50%
Prepayment Speed (%)		6.00%
Severity (%)		88.00%
Spread (bps)		3.002%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus with inputs [Member] | Other [Member] | Available-for-sale securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)		3.50%
Prepayment Speed (%)		2.50%
Severity (%)		87.50%
Spread (bps)		2.377%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus without inputs [Member] | Agency [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities		$ 809
Available-for-sale securities		72
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consensus without inputs [Member] | Alt-A and subprime private-label securities [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	154	39
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted cash flow with inputs [Member] | Alt-A and subprime private-label securities [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities		$ 45
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted cash flow with inputs [Member] | Alt-A and subprime private-label securities [Member] | Available-for-sale securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spread (bps)		3.61%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted cash flow with inputs [Member] | Alt-A and subprime private-label securities [Member] | Available-for-sale securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spread (bps)		4.50%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted cash flow with inputs [Member] | Alt-A and subprime private-label securities [Member] | Available-for-sale securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spread (bps)		4.06%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted cash flow with inputs [Member] | Mortgage revenue bonds [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities		$ 19
Available-for-sale securities		$ 435
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted cash flow with inputs [Member] | Mortgage revenue bonds [Member] | Trading securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spread (bps)		0.13%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted cash flow with inputs [Member] | Mortgage revenue bonds [Member] | Trading securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spread (bps)		2.682%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted cash flow with inputs [Member] | Mortgage revenue bonds [Member] | Trading securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spread (bps)		2.522%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted cash flow with inputs [Member] | Mortgage revenue bonds [Member] | Available-for-sale securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spread (bps)		(0.168%)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted cash flow with inputs [Member] | Mortgage revenue bonds [Member] | Available-for-sale securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spread (bps)		3.911%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted cash flow with inputs [Member] | Mortgage revenue bonds [Member] | Available-for-sale securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spread (bps)		2.60%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted cash flow with inputs [Member] | Other [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	$ 325	$ 348
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted cash flow with inputs [Member] | Other [Member] | Available-for-sale securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)		2.30%
Prepayment Speed (%)	1.60%	0.50%
Severity (%)	50.00%	95.00%
Spread (bps)	0.848%	1.90%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted cash flow with inputs [Member] | Other [Member] | Available-for-sale securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)		2.30%
Prepayment Speed (%)	2.50%	0.50%
Severity (%)	88.00%	95.00%
Spread (bps)	6.07%	4.50%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted cash flow with inputs [Member] | Other [Member] | Available-for-sale securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)		2.30%
Prepayment Speed (%)	2.50%	0.50%
Severity (%)	86.60%	95.00%
Spread (bps)	5.779%	4.491%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Discounted cash flow without inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Net derivatives		$ 21
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single vendor with inputs [Member] | Agency [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	$ 971
Available-for-sale securities	$ 112	$ 129
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single vendor with inputs [Member] | Agency [Member] | Trading securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Prepayment Speed (%)	0.00%
Spread (bps)	0.515%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single vendor with inputs [Member] | Agency [Member] | Trading securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Prepayment Speed (%)	177.00%
Spread (bps)	3.75%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single vendor with inputs [Member] | Agency [Member] | Trading securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Prepayment Speed (%)	160.00%
Spread (bps)	2.001%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single vendor with inputs [Member] | Agency [Member] | Available-for-sale securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Prepayment Speed (%)	0.00%	124.80%
Spread (bps)	1.50%	1.75%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single vendor with inputs [Member] | Agency [Member] | Available-for-sale securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Prepayment Speed (%)	175.70%	165.50%
Spread (bps)	2.10%	2.10%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single vendor with inputs [Member] | Agency [Member] | Available-for-sale securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Prepayment Speed (%)	147.10%	142.40%
Spread (bps)	1.823%	1.825%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single vendor with inputs [Member] | Alt-A and subprime private-label securities [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities		$ 93
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single vendor with inputs [Member] | Alt-A and subprime private-label securities [Member] | Available-for-sale securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)		2.50%
Prepayment Speed (%)		3.00%
Severity (%)		38.00%
Spread (bps)		2.661%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single vendor with inputs [Member] | Alt-A and subprime private-label securities [Member] | Available-for-sale securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)		8.00%
Prepayment Speed (%)		11.00%
Severity (%)		80.00%
Spread (bps)		3.068%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single vendor with inputs [Member] | Alt-A and subprime private-label securities [Member] | Available-for-sale securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)		3.80%
Prepayment Speed (%)		4.90%
Severity (%)		48.10%
Spread (bps)		2.971%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single vendor with inputs [Member] | Mortgage revenue bonds [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	$ 475	$ 684
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single vendor with inputs [Member] | Mortgage revenue bonds [Member] | Available-for-sale securities [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spread (bps)	(0.17%)	(0.168%)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single vendor with inputs [Member] | Mortgage revenue bonds [Member] | Available-for-sale securities [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spread (bps)	2.48%	3.369%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single vendor with inputs [Member] | Mortgage revenue bonds [Member] | Available-for-sale securities [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spread (bps)	0.39%	0.443%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single vendor without inputs [Member] | Mortgage revenue bonds [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities		$ 126
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Internal model [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Net derivatives		10
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Dealer mark without inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Net derivatives	$ 113	89
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Other valuation technique [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Net derivatives	21	(76)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Other valuation technique [Member] | Agency [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	35	26
Available-for-sale securities	96	34
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Other valuation technique [Member] | Alt-A and subprime private-label securities [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	40
Available-for-sale securities	77	79
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Other valuation technique [Member] | Mortgage revenue bonds [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Trading securities	1	2
Available-for-sale securities	196	27
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Other valuation technique [Member] | Other [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Available-for-sale securities	32	34
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single-Family [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	958	1,034
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single-Family [Member] | Consensus without inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	344	300
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single-Family [Member] | Build-Up without inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	406	516
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Single-Family [Member] | Other valuation technique [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	208	218
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Multifamily [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	158
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Multifamily [Member] | Build-Up with inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	$ 155	$ 163
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Multifamily [Member] | Build-Up with inputs [Member] | Mortgage loans [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spread (bps)	0.29%	0.55%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Multifamily [Member] | Build-Up with inputs [Member] | Mortgage loans [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spread (bps)	2.672%	3.052%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Multifamily [Member] | Build-Up with inputs [Member] | Mortgage loans [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Spread (bps)	1.058%	1.402%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Multifamily [Member] | Other valuation technique [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	$ 3
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Fannie Mae [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt	(376)	$ (347)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Fannie Mae [Member] | Senior floating [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt	(376)	(347)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Fannie Mae [Member] | Discounted cash flow without inputs [Member] | Senior floating [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt	(376)	(347)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt	(582)	(241)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member] | Discounted cash flow with inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt	$ (401)
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member] | Discounted cash flow with inputs [Member] | Long-term debt [Member] | Minimum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)	1.60%
Prepayment Speed (%)	5.40%
Severity (%)	28.00%
Spread (bps)	0.42%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member] | Discounted cash flow with inputs [Member] | Long-term debt [Member] | Maximum [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)	6.30%
Prepayment Speed (%)	100.00%
Severity (%)	95.00%
Spread (bps)	2.283%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member] | Discounted cash flow with inputs [Member] | Long-term debt [Member] | Weighted Average [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Default Rate (%)	4.60%
Prepayment Speed (%)	98.90%
Severity (%)	71.50%
Spread (bps)	0.787%
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member] | Consolidated Trusts [Member] | Other valuation technique [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt	$ (181)	$ (241)

Fair Value Level 3 Valuation -

Fair Value Level 3 Valuation - Nonrecurring (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	$ 10,596	$ 12,057
Significant Other Observable Inputs (Level 2) [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	101	509
Mortgage loans held for investment, at fair value	2,886,470	2,767,813
Total nonrecurring assets at fair value	2,948,237	2,844,940
Significant Unobservable Inputs (Level 3) [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	5,333	2,751
Mortgage loans held for investment, at fair value	315,719	316,742
Total nonrecurring assets at fair value	324,173	323,739
Fair Value, Measurements, Nonrecurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	14	250
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	2,993	1,088
Total nonrecurring assets at fair value	6,142	5,906
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Consensus without inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	1,113	1,025
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Single vendor without inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	1,880	54
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other valuation technique [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	0	9
Other assets	$ 2	$ 12
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Accepted Offers [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Number of properties measured	18.00%	19.00%
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Proprietary Home Price Model and Appraisals [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Number of properties measured	77.00%	75.00%
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Single-Family [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	$ 1,310	$ 1,792
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Single-Family [Member] | Other valuation technique [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	113	99
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Single-Family [Member] | Internal model [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	1,623	2,816
Acquired property, net	319	476
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Single-Family [Member] | Accepted Offers [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	218	340
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Single-Family [Member] | Appraisals [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	438	571
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Single-Family [Member] | Walk Forwards [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	222	306
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Multifamily [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	195	198
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Multifamily [Member] | Other valuation technique [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	4	3
Acquired property, net	19	0
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Multifamily [Member] | Broker Price Opinions [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	28	25
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Multifamily [Member] | Asset Manager Estimate [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	$ 163	$ 170

Fair Value of Financial Instrum

Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value Measurement [Domain]
Financial assets [Abstract]
Netting adjustment	$ (4,272)	$ (4,514)
Financial liabilities [Abstract]
Netting adjustment	(4,979)	(6,844)
Mortgage loans held for investment, at fair value	10,596	12,057
Netting adjustment	(4,272)	(4,514)
Netting adjustment	(4,979)	(6,844)
Fannie Mae [Member]
Financial liabilities [Abstract]
Long-term debt	8,186	9,582
Consolidated Trusts [Member]
Financial liabilities [Abstract]
Long-term debt	30,493	36,524
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial assets [Abstract]
Cash and cash equivalents and restricted cash	35,060	41,477
Federal funds sold and securities purchased under agreements to resell or similar arrangements	0	0
Trading securities	29,222	32,317
Available-for-sale securities	0	0
Mortgage loans held for sale	0	0
Mortgage loans held for investment, at fair value	0	0
Advances to lenders	0	0
Derivatives assets at fair value	0	0
Guaranty assets and buy-ups	0	0
Total financial assets	64,282	73,794
Financial liabilities [Abstract]
Derivatives liabilities at fair value	0	0
Guaranty obligations	0	0
Total financial liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fannie Mae [Member]
Financial liabilities [Abstract]
Short-term debt	0	0
Long-term debt	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Consolidated Trusts [Member]
Financial liabilities [Abstract]
Short-term debt	0	0
Long-term debt	0	0
Significant Other Observable Inputs (Level 2) [Member]
Financial assets [Abstract]
Cash and cash equivalents and restricted cash	25,200	20,700
Federal funds sold and securities purchased under agreements to resell or similar arrangements	19,470	30,415
Trading securities	4,256	7,118
Available-for-sale securities	3,530	6,210
Mortgage loans held for sale	101	509
Mortgage loans held for investment, at fair value	2,886,470	2,767,813
Advances to lenders	4,936	7,156
Derivatives assets at fair value	4,274	5,019
Guaranty assets and buy-ups	0	0
Total financial assets	2,948,237	2,844,940
Financial liabilities [Abstract]
Derivatives liabilities at fair value	5,272	7,921
Guaranty obligations	0	0
Total financial liabilities	3,302,681	3,243,215
Significant Other Observable Inputs (Level 2) [Member] | Fannie Mae [Member]
Financial liabilities [Abstract]
Short-term debt	33,379	34,998
Long-term debt	249,780	298,980
Significant Other Observable Inputs (Level 2) [Member] | Consolidated Trusts [Member]
Financial liabilities [Abstract]
Short-term debt	0	0
Long-term debt	3,014,250	2,901,316
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	1,201	1,127
Available-for-sale securities	1,313	2,153
Mortgage loans held for sale	5,333	2,751
Mortgage loans held for investment, at fair value	315,719	316,742
Advances to lenders	2	352
Derivatives assets at fair value	169	182
Guaranty assets and buy-ups	436	432
Total financial assets	324,173	323,739
Financial liabilities [Abstract]
Derivatives liabilities at fair value	35	138
Guaranty obligations	456	710
Total financial liabilities	42,389	38,870
Significant Unobservable Inputs (Level 3) [Member] | Fannie Mae [Member]
Financial liabilities [Abstract]
Short-term debt	0	0
Long-term debt	837	770
Significant Unobservable Inputs (Level 3) [Member] | Consolidated Trusts [Member]
Financial liabilities [Abstract]
Short-term debt	378	584
Long-term debt	40,683	36,668
Carrying Value [Member]
Financial assets [Abstract]
Cash and cash equivalents and restricted cash	60,260	62,177
Federal funds sold and securities purchased under agreements to resell or similar arrangements	19,470	30,415
Trading securities	34,679	40,562
Available-for-sale securities	4,843	8,363
Mortgage loans held for sale	4,988	2,899
Mortgage loans held for investment, at fair value	3,173,537	3,076,854
Advances to lenders	4,938	7,494
Derivatives assets at fair value	171	687
Guaranty assets and buy-ups	149	158
Total financial assets	3,303,035	3,229,609
Financial liabilities [Abstract]
Derivatives liabilities at fair value	328	1,215
Guaranty obligations	258	280
Total financial liabilities	3,330,640	3,263,811
Carrying Value [Member] | Fannie Mae [Member]
Financial liabilities [Abstract]
Short-term debt	33,377	34,995
Long-term debt	243,375	292,102
Carrying Value [Member] | Consolidated Trusts [Member]
Financial liabilities [Abstract]
Short-term debt	379	584
Long-term debt	3,052,923	2,934,635
Estimate of Fair Value Measurement [Member]
Financial assets [Abstract]
Cash and cash equivalents and restricted cash	60,260	62,177
Federal funds sold and securities purchased under agreements to resell or similar arrangements	19,470	30,415
Trading securities	34,679	40,562
Available-for-sale securities	4,843	8,363
Mortgage loans held for sale	5,434	3,260
Mortgage loans held for investment, at fair value	3,202,189	3,084,555
Advances to lenders	4,938	7,508
Derivatives assets at fair value	171	687
Guaranty assets and buy-ups	436	432
Total financial assets	3,332,420	3,237,959
Financial liabilities [Abstract]
Derivatives liabilities at fair value	328	1,215
Guaranty obligations	456	710
Total financial liabilities	3,340,091	3,275,241
Estimate of Fair Value Measurement [Member] | Fannie Mae [Member]
Financial liabilities [Abstract]
Short-term debt	33,379	34,998
Long-term debt	250,617	299,750
Estimate of Fair Value Measurement [Member] | Consolidated Trusts [Member]
Financial liabilities [Abstract]
Short-term debt	378	584
Long-term debt	$ 3,054,933	$ 2,937,984

Fair Value Option (Details)

Fair Value Option (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Option, Quantitative Disclosures [Line Items]
Mortgage loans held for investment, at fair value	$ 10,596	$ 12,057
Fair value of nonaccrual loans	227	200
Difference between unpaid principal balance and the fair value of nonaccrual loans	46	34
Fair value of loans that are 90 days past due	159	152
Difference between unpaid principal balance and the fair value of these 90 days or more days past due loans	$ 34	$ 25
Single-Family [Member] | Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Serious delinquency: days past due	90 days	90 days
Consolidated Trusts [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Long-term debt, fair value	$ 30,493	$ 36,524
Fannie Mae [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Long-term debt, fair value	8,186	9,582
Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Mortgage loans held for investment, at fair value	10,596	12,057
Loans, unpaid principal balance	10,246	11,688
Long-term debt [Member] | Consolidated Trusts [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Long-term debt, fair value	30,493	36,524
Long-Term Debt, unpaid principal balance	27,717	33,055
Long-term debt [Member] | Fannie Mae [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Long-term debt, fair value	8,186	9,582
Long-Term Debt, unpaid principal balance	$ 7,368	$ 9,090

Fair Value Changes in FV under

Fair Value Changes in FV under the FV Option (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in instrument-specific credit risk	$ (249)	$ (625)	$ 125
Other changes in fair value	91	265	(45)
Fair value gains (losses), net	(158)	(360)	80
Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in instrument-specific credit risk - Loans	67	23	86
Other changes in fair value	69	72	(191)
Fair value gains (losses), net	136	95	(105)
Long-term debt [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in instrument-specific credit risk - Long-Term Debt	(316)	(648)	39
Other changes in fair value	22	193	146
Fair value gains (losses), net	$ (294)	$ (455)	$ 185

Commitments and Contingencie112

Commitments and Contingencies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Rent expenses for operating leases	$ 61	$ 50	$ 47

Commitments and Contingencies F

Commitments and Contingencies Fiscal Year Maturity Schedule (Details) $ in Millions	Dec. 31, 2017USD ($)
Loans and Mortgage-Related Securities [Abstract]
2,018	$ 73,130
2,019	0
2,020	0
2,021	0
2,022	0
Thereafter	0
Total	73,130
Operating Leases [Abstract]
2,018	41
2,019	48
2,020	56
2,021	56
2,022	58
Thereafter	609
Total	868
Other [Abstract]
2,018	98
2,019	57
2,020	73
2,021	14
2,022	1
Thereafter	0
Total	243
Mortgage commitment derivatives
Loans and Mortgage-Related Securities [Abstract]
Total	$ 72,700

Selected Quarterly Financial114

Selected Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest income:
Trading securities	$ 193	$ 195	$ 176	$ 142	$ 128	$ 140	$ 128	$ 120	$ 706	$ 516	$ 444
Available-for-sale securities	66	77	91	101	113	134	170	203	335	620	1,156
Mortgage loans interest income	27,214	27,047	27,011	27,047	25,814	25,611	26,256	26,961	108,319	104,642	107,699
Other	145	142	115	94	83	66	46	48	496	243	143
Total interest income	27,618	27,461	27,393	27,384	26,138	25,951	26,600	27,332	109,856	106,021	109,442
Interest expense:
Short-term debt interest expense	(77)	(72)	(57)	(44)	(42)	(56)	(57)	(51)	(250)	(206)	(146)
Long-term debt interest expense	(22,430)	(22,115)	(22,334)	(21,994)	(20,291)	(20,460)	(21,257)	(22,512)	(88,873)	(84,520)	(87,887)
Total interest expense	(22,507)	(22,187)	(22,391)	(22,038)	(20,333)	(20,516)	(21,314)	(22,563)	(89,123)	(84,726)	(88,033)
Net interest income	5,111	5,274	5,002	5,346	5,805	5,435	5,286	4,769	20,733	21,295	21,409
Benefit (provision) for credit losses	560	(182)	1,267	396	(1,303)	673	1,601	1,184	2,041	2,155	795
Net interest income after benefit (provision) for credit losses	5,671	5,092	6,269	5,742	4,502	6,108	6,887	5,953	22,774	23,450	22,204
Investment gains (losses), net	833	313	385	(9)	322	467	398	69	1,522	1,256	1,336
Fair value gains (losses), net	(191)	(289)	(691)	(40)	3,890	(491)	(1,667)	(2,813)	(1,211)	(1,081)	(1,767)
Fee and other income	431	1,194	353	249	414	175	174	203	2,227	966	1,348
Non-interest income (loss)	1,073	1,218	47	200	4,626	151	(1,095)	(2,541)	2,538	1,141	917
Administrative expenses:
Salaries and employee benefits	(321)	(331)	(332)	(344)	(319)	(322)	(331)	(364)	(1,328)	(1,336)	(1,319)
Professional services	(252)	(218)	(234)	(229)	(271)	(237)	(232)	(215)	(933)	(955)	(984)
Other administrative expenses	(130)	(115)	(120)	(111)	(124)	(102)	(115)	(109)	(476)	(450)	(747)
Total administrative expenses	(703)	(664)	(686)	(684)	(714)	(661)	(678)	(688)	(2,737)	(2,741)	(3,050)
Foreclosed property expense	(130)	(140)	(34)	(217)	(137)	(110)	(63)	(334)	(521)	(644)	(1,629)
Temporary Payroll Cut Continuation Act of 2011 (TCCA) fees	(544)	(531)	(518)	(503)	(487)	(465)	(453)	(440)	(2,096)	(1,845)	(1,621)
Other expenses, net	(411)	(427)	(291)	(382)	(210)	(300)	(254)	(264)	(1,511)	(1,028)	(613)
Total expenses	(1,788)	(1,762)	(1,529)	(1,786)	(1,548)	(1,536)	(1,448)	(1,726)	(6,865)	(6,258)	(6,913)
Income before federal income taxes	4,956	4,548	4,787	4,156	7,580	4,723	4,344	1,686	18,447	18,333	16,208
Provision for federal income taxes	(11,489)	(1,525)	(1,587)	(1,383)	(2,545)	(1,527)	(1,398)	(550)	(15,984)	(6,020)	(5,253)
Net income (loss) attributable to Fannie Mae	(6,533)	3,023	3,200	2,773	5,035	3,196	2,946	1,136	2,463	12,313	10,954
Dividends distributed or available for distribution to senior preferred stockholder	0	(3,048)	(3,117)	(2,779)	(5,471)	(2,977)	(2,869)	(919)	(8,944)	(12,236)	(11,216)
Net income (loss) attributable to common stockholders	$ (6,533)	$ (25)	$ 83	$ (6)	$ (436)	$ 219	$ 77	$ 217	$ (6,481)	$ 77	$ (262)
Earnings (loss) per share: Basic	$ (1.13)	$ 0	$ 0.01	$ 0	$ (0.08)	$ 0.04	$ 0.01	$ 0.04	$ (1.12)	$ 0.01	$ (0.05)
Earnings (loss) per share: Diluted	$ (1.13)	$ 0	$ 0.01	$ 0	$ (0.08)	$ 0.04	$ 0.01	$ 0.04	$ (1.12)	$ 0.01	$ (0.05)
Weighted-average common shares outstanding: Basic	5,762	5,762	5,762	5,762	5,762	5,762	5,762	5,762
Weighted-average common shares outstanding: Diluted	5,762	5,762	5,893	5,762	5,762	5,893	5,893	5,893	5,762	5,893	5,762