Summary of Significant Accounting Policies Narratives(Details) (USD $)	3 Months Ended			6 Months Ended				6 Months Ended	3 Months Ended	6 Months Ended							3 Months Ended		6 Months Ended			3 Months Ended
	Jun. 30, 2012	Jun. 30, 2011		Jun. 30, 2012	Jun. 30, 2011		Dec. 31, 2011	Jun. 30, 2012 Out Of Period Adjustment [Member]	Jun. 30, 2011 US Treasury [Member]	Jun. 30, 2011 US Treasury [Member]	Jun. 30, 2012 US Treasury [Member]	Dec. 31, 2009 US Treasury [Member]	Jun. 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]	Jun. 30, 2012 US Treasury [Member] New Issue Bond [Member]	Dec. 31, 2011 US Treasury [Member] New Issue Bond [Member]	Jun. 30, 2012 Freddie Mac [Member]	Jun. 30, 2011 Freddie Mac [Member]	Jun. 30, 2012 Freddie Mac [Member]	Jun. 30, 2011 Freddie Mac [Member]	Dec. 31, 2011 Freddie Mac [Member]	Jun. 30, 2012 Net Other-than-Temporary Impairments [Member]
Accounting Policies [Abstract]
Deficit of core capital over statutory minimum capital requirement	$ 145,100,000,000			$ 145,100,000,000			$ 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	75,200,000,000
Initial aggregate liquidation preference of senior preferred stock held by US Treasury											1,000,000,000
Aggregate liquidation preference of senior preferred stock											117,100,000,000
Maximum commitment from US Treasury pursuant to the senior preferred stock purchase agreement											200,000,000,000
Total available funding from US Treasury pursuant to the senior preferred stock agreement after 2012											124,800,000,000
Percentage of common shares attributable to warrants issued to US Treasury as percentage to total diluted common shares											79.90%
Home Affordable Modification Program administrative expense reimbursements	26,000,000	25,000,000		48,000,000	60,000,000
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													2,500,000,000	3,000,000,000	6,900,000,000	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%
Loss of principal or interest under Treasury's Temporary Credit and Liquid Facilitiy and New Issue Bond Progams											0
Increase of guarantee fee rate resulting from the Temporary Payroll Tax Cut Continuation Act of 2011.											0.10%
Liability To Treasury Related To Increase In Single-Family Guaranty Fee Resulting From Temporary Payroll Tax Cut Continuation Act Of 2011											26,000,000
Fair value of mortgage-backed securities																	14,000,000,000		14,000,000,000		15,600,000,000
Interest receivable	9,668,000,000			9,668,000,000			10,000,000,000										60,000,000		60,000,000		69,000,000
Investment Income, Interest																	142,000,000	172,000,000	295,000,000	360,000,000
Increase in other-than-temporary impairment expense due to change in assumptions used to project cash flow estimate on Alt-A and supbrime private-label securities																						500,000,000
Securities Received as Collateral [Abstract]
Collateral held on reverse repurchase agreements	36,100,000,000			36,100,000,000			49,500,000,000
Fair value of non-cash collateral	36,200,000,000			36,200,000,000			50,100,000,000
Fair value of non-cash collateral that can be sold or repledged	27,100,000,000			27,100,000,000			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	$ (3,041,000,000)	$ 6,537,000,000	[1]	$ (1,041,000,000)	$ 17,091,000,000	[1]		$ 1,100,000,000

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