Financial Guarantees Risk Characteristics - Single-Family (Details) (Single-Family [Member])	Dec. 31, 2012		Dec. 31, 2011
Guaranty Book of Business [Member] | Conventional Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of book of business	100.00%	[1],[2]	100.00%	[1],[2]
Seriously delinquent, percentage (loan count)	3.29%	[3],[4],[5]	3.91%	[3],[4],[5]
Percentage of loans with detailed loan level information	99.00%		99.00%
Guaranty Book of Business [Member] | Conventional Loan [Member] | 2005 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of book of business	5.00%	[3],[6]	7.00%	[3],[6]
Seriously delinquent, percentage (loan count)	7.79%	[3],[5],[7]	7.27%	[3],[5],[7]
Guaranty Book of Business [Member] | Conventional Loan [Member] | 2006 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of book of business	5.00%	[3],[6]	7.00%	[3],[6]
Seriously delinquent, percentage (loan count)	12.15%	[3],[5],[7]	11.81%	[3],[5],[7]
Guaranty Book of Business [Member] | Conventional Loan [Member] | 2007 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of book of business	7.00%	[3],[6]	10.00%	[3],[6]
Seriously delinquent, percentage (loan count)	12.99%	[3],[5],[7]	12.62%	[3],[5],[7]
Guaranty Book of Business [Member] | Conventional Loan [Member] | 2008 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of book of business	5.00%	[3],[6]	7.00%	[3],[6]
Seriously delinquent, percentage (loan count)	6.63%	[3],[5],[7]	5.64%	[3],[5],[7]
Guaranty Book of Business [Member] | Conventional Loan [Member] | All Other Vintages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of book of business	78.00%	[3],[6]	69.00%	[3],[6]
Seriously delinquent, percentage (loan count)	1.36%	[3],[5],[7]	1.59%	[3],[5],[7]
Guaranty Book of Business [Member] | Conventional Loan [Member] | Alt-A [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of book of business	6.00%	[3],[6]	7.00%	[3],[6]
Seriously delinquent, percentage (loan count)	11.36%	[3],[5],[7]	12.43%	[3],[5],[7]
Guaranty Book of Business [Member] | Conventional Loan [Member] | Subprime [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Seriously delinquent, percentage (loan count)	20.60%	[3],[5],[7]	23.18%	[3],[5],[7]
Guaranty Book of Business [Member] | Conventional Loan [Member] | Arizona
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of book of business	2.00%	[3],[6]	2.00%	[3],[6]
Seriously delinquent, percentage (loan count)	2.14%	[3],[5],[7]	3.65%	[3],[5],[7]
Guaranty Book of Business [Member] | Conventional Loan [Member] | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of book of business	19.00%	[3],[6]	19.00%	[3],[6]
Seriously delinquent, percentage (loan count)	1.69%	[3],[5],[7]	2.46%	[3],[5],[7]
Guaranty Book of Business [Member] | Conventional Loan [Member] | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of book of business	6.00%	[3],[6]	6.00%	[3],[6]
Seriously delinquent, percentage (loan count)	10.06%	[3],[5],[7]	11.80%	[3],[5],[7]
Guaranty Book of Business [Member] | Conventional Loan [Member] | Nevada
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of book of business	1.00%	[3],[6]	1.00%	[3],[6]
Seriously delinquent, percentage (loan count)	6.70%	[3],[5],[7]	7.42%	[3],[5],[7]
Guaranty Book of Business [Member] | Conventional Loan [Member] | Select Midwest States [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of book of business	10.00%	[3],[6],[8]	10.00%	[3],[6],[8]
Seriously delinquent, percentage (loan count)	3.51%	[3],[5],[7],[8]	4.39%	[3],[5],[7],[8]
Guaranty Book of Business [Member] | Conventional Loan [Member] | All Other States [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of book of business	62.00%	[3],[6]	62.00%	[3],[6]
Seriously delinquent, percentage (loan count)	2.85%	[3],[5],[7]	3.18%	[3],[5],[7]
Guaranty Book of Business [Member] | Conventional Loan [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 100% [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of book of business	13.00%	[3],[6]	18.00%	[3],[6]
Seriously delinquent, percentage (loan count)	13.42%	[3],[5],[7]	13.76%	[3],[5],[7]
Maximum [Member] | Guaranty Book of Business [Member] | Conventional Loan [Member] | Subprime [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of book of business	0.50%	[3],[6],[9]	0.50%	[3],[6],[9]
Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Serious delinquency, days past due	90 days		90 days
Minimum [Member] | Guaranty Book of Business [Member] | Conventional Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of loans with detailed loan level information	99.00%		99.00%
Original LTV Ratio Greater Than 90% and FICO Score Less Than 620 [Member] | Guaranty Book of Business [Member] | Conventional Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of book of business	1.00%	[3],[6]	1.00%	[3],[6]
Seriously delinquent, percentage (loan count)	14.76%	[3],[5],[7]	18.67%	[3],[5],[7]

[1] 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, 2012 and 2011.

[2] Midwest includes IL, IN, IA, MI, MN, NE, ND, OH, SD, WI; Northeast includes CT, DE, ME, MA, NH, NJ, NY, PA, PR, RI, VT, VI; Southeast includes AL, DC, FL, GA, KY, MD, MS, NC, SC, TN, VA, WV; Southwest includes AZ, AR, CO, KS, LA, MO, NM, OK, TX, UT; West includes AK, CA, GU, HI, ID, MT, NV, OR, WA and WY.

[3] 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, 2012 and 2011.

[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.

[5] Consists of single-family conventional loans that were 90 days or more past due or in the foreclosure process as of December 31, 2012 and 2011.

[6] 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.

[7] Calculated based on the number of single-family conventional loans that were seriously delinquent divided by the total number of single-family conventional loans for each category included in our guaranty book of business.

[8] Consists of Illinois, Indiana, Michigan, and Ohio.

[9] Represents less than 0.5% of the single-family conventional guaranty book of business.