Financial Guarantees Delinquency Status - Single-Family (Details) (Single-Family [Member])	Mar. 31, 2013		Dec. 31, 2012
Guaranty Book of Business [Member] | Conventional Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30 days delinquent, percentage (unpaid principal balance)	1.54%	[1],[2]	1.75%	[1],[2]
60 days delinquent, percentage (unpaid principal balance)	0.50%	[1],[2]	0.63%	[1],[2]
Seriously delinquent, percentage (unpaid principal balance)	3.33%	[1],[2],[3]	3.66%	[1],[2],[3]
30 days delinquent, percentage (loan count)	1.72%	[2],[4]	1.96%	[2],[4]
60 days delinquent, percentage (loan count)	0.53%	[2],[4]	0.66%	[2],[4]
Seriously delinquent, percentage (loan count)	3.02%	[2],[3],[4]	3.29%	[2],[3],[4]
Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Serious delinquency, days past due	90 days		90 days

[1] 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.

[2] 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 March 31, 2013 and December 31, 2012.

[3] Consists of single-family conventional loans that were 90 days or more past due or in the foreclosure process, as of March 31, 2013 and December 31, 2012.

[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.