Expected Losses to be Paid (First Lien Liquidation Rates) (Details 5)				3 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Total first lien	Dec. 31, 2012 Alt- A and Prime	Dec. 31, 2011 Alt- A and Prime	Dec. 31, 2010 Alt- A and Prime	Dec. 31, 2012 First mortgage, option adjustable rate mortgage	Dec. 31, 2011 First mortgage, option adjustable rate mortgage	Dec. 31, 2010 First mortgage, option adjustable rate mortgage	Dec. 31, 2012 First mortgage, subprime	Dec. 31, 2011 First mortgage, subprime	Dec. 31, 2010 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%	50.00%	50.00%	30.00%	30.00%	45.00%
Liquidation rate for 60 - 89 days delinquent category (as a percent)					55.00%	55.00%	65.00%	65.00%	65.00%	65.00%	45.00%	45.00%	65.00%
Liquidation rate for 90 days delinquent category (as a percent)					65.00%	65.00%	75.00%	75.00%	75.00%	75.00%	60.00%	60.00%	70.00%
Liquidation rate for bankruptcy delinquent category (as a percent)					55.00%	55.00%	75.00%	70.00%	70.00%	75.00%	50.00%	50.00%	70.00%
Liquidation rate for foreclosure category (as a percent)					85.00%	85.00%	85.00%	85.00%	85.00%	85.00%	80.00%	80.00%	85.00%
Liquidation rate for real estate owned (as a percent)	100.00%	100.00%	100.00%
Projected period of loan liquidations (in years)				2 years