Loss And Loss Adjustment Expense Reserves (RMBS Reserves) (Narrative) (Detail) (USD $)	1 Months Ended					9 Months Ended
	Aug. 31, 2012	Sep. 30, 2012	Sep. 30, 2012 September 2012 to February 2013 [Member] Scenario, Forecast [Member]	Sep. 30, 2012 September 2012 to February 2013 [Member] Linear reduction in original value [Member] Scenario, Forecast [Member]	Sep. 30, 2012 November 2012 To March 31,2014 [Member]	Sep. 30, 2012 RMBS And HELOC And CES [Member]	Sep. 30, 2012 RMBS And HELOC And CES [Member] September 2012 to March 2013 [Member] M	Sep. 30, 2012 RMBS And HELOC And CES [Member] September 2012 to February 2013 [Member] Scenario, Forecast [Member] M	Sep. 30, 2012 First-Lien RMBS Reserves [Member] D	Sep. 30, 2012 First-Lien RMBS Reserves [Member] Alt-A [Member]	Sep. 30, 2012 First-Lien RMBS Reserves [Member] Foreclosure [Member]	Sep. 30, 2012 First-Lien RMBS Reserves [Member] Real Estate Owned [Member]	Sep. 30, 2012 First-Lien RMBS Reserves [Member] Bankruptcy [Member]	Sep. 30, 2012 First-Lien RMBS Reserves [Member] September 2012 to February 2013 [Member] Scenario, Forecast [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Charged-off loans recovery values		$ 0
Assumed roll rate for ninety plus day delinquent loans						95.00%
Period of elevated delinquency and loss, beginning, months							6
Percentage of loans in 30-59 days delinquent bucket	10.00%
Percentage of loans charged-off	30.00%
Percentage of Current Roll to Loss for the transaction	3.00%
Decrease in percentage of Current Roll to Loss for transaction			25.00%	0.75%										25.00%
Current Roll to Loss					0.00%
Period of elevated delinquency and loss for stress case, additional months								6
Addition to case basis reserves before considering potential recoveries						125,000,000
Delinquency period charged off on transaction specific basis, days									90
Assumed roll rate for loans											90.00%	90.00%	75.00%
90+ day roll rate to loss set									90.00%
Percentage of loss after declining over a 24-month period										25.00%
Change in recoveries of actual and expected payments related to ineligible mortgages						$ 154,000,000