Expected Losses to be Paid (First Lien Liquidation Rates) (Details 5)			3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Total first lien	Mar. 31, 2013 Alt- A and Prime	Dec. 31, 2012 Alt- A and Prime	Mar. 31, 2013 First mortgage, option adjustable rate mortgage	Dec. 31, 2012 First mortgage, option adjustable rate mortgage	Mar. 31, 2013 First mortgage, subprime	Dec. 31, 2012 First mortgage, subprime
Guarantor Obligations [Line Items]
Minimum percentage for categorizing an Option ARM			66.00%
Liquidation rate for 30 - 59 days delinquent category (as a percent)				35.00%	35.00%	50.00%	50.00%	30.00%	30.00%
Liquidation rate for 60 - 89 days delinquent category (as a percent)				55.00%	55.00%	65.00%	65.00%	45.00%	45.00%
Liquidation rate for 90 days delinquent category (as a percent)				65.00%	65.00%	75.00%	75.00%	60.00%	60.00%
Liquidation rate for bankruptcy delinquent category (as a percent)				55.00%	55.00%	70.00%	70.00%	50.00%	50.00%
Liquidation rate for foreclosure category (as a percent)				85.00%	85.00%	85.00%	85.00%	80.00%	80.00%
Liquidation rate for real estate owned (as a percent)	100.00%	100.00%
Projected period of loan liquidations (in years)			2 years