Summary of Significant Accounting Policies Narratives(Details) (USD $)	3 Months Ended			9 Months Ended				3 Months Ended	6 Months Ended	9 Months Ended	3 Months Ended		9 Months Ended							3 Months Ended		9 Months Ended			3 Months Ended	9 Months Ended		3 Months Ended
	Sep. 30, 2012	Sep. 30, 2011		Sep. 30, 2012	Sep. 30, 2011		Dec. 31, 2011	Sep. 30, 2012 Out-of-Period Adjustment [Member]	Jun. 30, 2012 Out-of-Period Adjustment [Member]	Sep. 30, 2012 Out-of-Period Adjustment [Member]	Sep. 30, 2012 US Treasury [Member]	Sep. 30, 2011 US Treasury [Member]	Sep. 30, 2012 US Treasury [Member]	Sep. 30, 2011 US Treasury [Member]	Dec. 31, 2009 US Treasury [Member]	Sep. 30, 2012 US Treasury [Member] Temporary Credit and Liquidity Facilities Program [Member]	Dec. 31, 2011 US Treasury [Member] Temporary Credit and Liquidity Facilities Program [Member]	Sep. 30, 2012 US Treasury [Member] New Issue Bond [Member]	Dec. 31, 2011 US Treasury [Member] New Issue Bond [Member]	Sep. 30, 2012 Freddie Mac [Member]	Sep. 30, 2011 Freddie Mac [Member]	Sep. 30, 2012 Freddie Mac [Member]	Sep. 30, 2011 Freddie Mac [Member]	Dec. 31, 2011 Freddie Mac [Member]	Sep. 30, 2012 Loan Loss Models Update [Member]	Sep. 30, 2012 Single-Family Collectively Impaired Loan Loss Models Update [Member] [Member]	Sep. 30, 2012 Single-Family Individually Impaired Loan Loss Models Update [Member]	Jun. 30, 2012 Net Other-than-Temporary Impairments [Member]
Accounting Policies [Abstract]
Deficit of core capital over statutory minimum capital requirement	$ 146,400,000,000			$ 146,400,000,000			$ 148,400,000,000
Number of days FHFA must place us into receivership	60 days			60 days
Related Parties [Line Items]
Aggregate funding received from US Treasury pursuant to the senior preferred stock purchase agreement											116,100,000,000		116,100,000,000		75,200,000,000
Initial aggregate liquidation preference of senior preferred stock held by US Treasury											1,000,000,000		1,000,000,000
Aggregate liquidation preference of senior preferred stock											117,100,000,000		117,100,000,000
Maximum commitment from US Treasury pursuant to the senior preferred stock purchase agreement											200,000,000,000		200,000,000,000
Total available funding from US Treasury pursuant to the senior preferred stock agreement after 2012											124,800,000,000		124,800,000,000
Senior Preferred Stock dividend rate in effect through December 31, 2012													10.00%
Capital reserve amount for 2013 per the Senior Preferred Stock Purchase Agreement Amendment											3,000,000,000		3,000,000,000
Annual reduction of capital reserve from 2013 to 2018 based on Senior Preferred Stock Purchase Agreement Amendment											600,000,000		600,000,000
Percentage of common shares attributable to warrants issued to US Treasury as percentage to total diluted common shares											79.90%		79.90%
Home Affordable Modification Program administrative expense reimbursements	27,000,000	30,000,000		75,000,000	90,000,000
Proceeds from income tax refunds														1,100,000,000
Income tax benefit recognized from our settlement of 2007 and 2008 tax years with the IRS												90,000,000		90,000,000
Principal and Interest Outstanding																1,900,000,000	3,000,000,000	6,800,000,000	7,500,000,000
Percentage of initial principal loss US Treasury will bear for Temporary Credit and Liquidity Facilities and New Issue Bond Programs											35.00%		35.00%
Loss of principal or interest under Treasury's Temporary Credit and Liquid Facilitiy and New Issue Bond Progams											0		0
Increase of guarantee fee rate resulting from the Temporary Payroll Tax Cut Continuation Act of 2011.											0.10%		0.10%
TCCA guaranty fee											78,000,000		104,000,000
Liability To Treasury for the remittance of TCCA-related guaranty fees											78,000,000		78,000,000
TCCA guaranty fee remitted													26,000,000
Fair value of mortgage-backed securities																				13,000,000,000		13,000,000,000		15,600,000,000
Interest receivable	9,963,000,000			9,963,000,000			10,000,000,000													54,000,000		54,000,000		69,000,000
Investment income, interest																				132,000,000	174,000,000	427,000,000	534,000,000
Increase (decrease) to the allowance for loan losses and provision for credit losses																									3,500,000,000	(1,500,000,000)	5,000,000,000
Increase in other-than-temporary impairment expense due to change in assumptions used to project cash flow estimate on Alt-A and subprime private-label securities																												500,000,000
Securities Received as Collateral [Abstract]
Collateral held on reverse repurchase agreements	54,300,000,000			54,300,000,000			49,500,000,000
Fair value of non-cash collateral	54,800,000,000			54,800,000,000			50,100,000,000
Fair value of non-cash collateral that can be sold or repledged	30,000,000,000			30,000,000,000			20,000,000,000
Fair value of securities received as collateral that have been sold or repledged	0			0			0
Out-of-period adjustment to (Benefit) provision for credit losses	$ 2,079,000,000	$ 4,151,000,000	[1]	$ 1,038,000,000	$ 21,242,000,000	[1]		$ 850,000,000	$ 1,100,000,000	$ 1,900,000,000

[1] Prior period amounts have been reclassified to conform to the current period presentation.