Financial Guarantees Delinquency Status - Single-Family (Details) (Single-Family [Member])	Sep. 30, 2012		Dec. 31, 2011
Guaranty Book of Business [Member] | Conventional Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 days delinquent, percentage (unpaid principal balance)	1.91%	[1],[2]	1.98%	[1],[2]
60 days delinquent, percentage (unpaid principal balance)	0.65%	[1],[2]	0.73%	[1],[2]
Seriously delinquent, percentage (unpaid principal balance)	3.82%	[1],[2],[3]	4.47%	[1],[2],[3]
30 days delinquent, percentage (loan count)	2.12%	[1],[4]	2.17%	[1],[4]
60 days delinquent, percentage (loan count)	0.68%	[1],[4]	0.74%	[1],[4]
Seriously delinquent, percentage (loan count)	3.41%	[1],[3],[4]	3.91%	[1],[3],[4]
Percentage of loans with detailed loan level information	99.00%		99.00%
Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Serious delinquency, days past due	90 days		90 days

[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 September 30, 2012 and December 31, 2011.

[2] 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.

[3] Consists of single-family conventional loans that were 90 days or more past due or in the foreclosure process, as of September 30, 2012 and December 31, 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.