Loss And Loss Adjustment Expense Reserves (RMBS Reserves) (Narrative) (Detail) (USD $)	1 Months Ended					12 Months Ended
	Nov. 30, 2012	Dec. 31, 2012	Dec. 31, 2012 December 2012 to May 2013 [Member] Scenario, Forecast [Member]	Dec. 31, 2012 December 2012 to May 2013 [Member] Linear reduction in original value [Member] Scenario, Forecast [Member]	Dec. 31, 2012 March 31, 2013 to June 30, 2014 [Member]	Dec. 31, 2012 RMBS And HELOC And CES [Member]	Dec. 31, 2012 RMBS And HELOC And CES [Member] December 2012 to May 2013 [Member] M	Dec. 31, 2012 RMBS And HELOC And CES [Member] December 2012 to May 2013 [Member] Scenario, Forecast [Member] M	Dec. 31, 2012 First-Lien RMBS Reserves [Member] D	Dec. 31, 2012 First-Lien RMBS Reserves [Member] Alt-A [Member]	Dec. 31, 2012 First-Lien RMBS Reserves [Member] Foreclosure [Member]	Dec. 31, 2012 First-Lien RMBS Reserves [Member] Real Estate Owned [Member]	Dec. 31, 2012 First-Lien RMBS Reserves [Member] Bankruptcy [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Charged-off loans recovery values		$ 0
Assumed roll rate for ninety plus day delinquent loans excluding foreclosures and Real Estate Owned						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%
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 for elevated delinquency and loss for stress case						110,000,000
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						$ 454,000,000