Loss And Loss Adjustment Expense Reserves (RMBS Reserves) (Narrative) (Details) (USD $)	1 Months Ended	3 Months Ended			6 Months Ended	0 Months Ended	3 Months Ended			6 Months Ended	7 Months Ended	12 Months Ended	6 Months Ended
	Feb. 29, 2012	Mar. 31, 2012	Mar. 31, 2012 RMBS And HELOC And CES [Member]	Mar. 31, 2012 First-Lien RMBS Reserves [Member]	Aug. 31, 2012 First-Lien RMBS Reserves [Member]	Feb. 29, 2012 ALT-A [Member] First-Lien RMBS Reserves [Member]	Mar. 31, 2012 Foreclosure [Member] First-Lien RMBS Reserves [Member]	Mar. 31, 2012 Real Estate Owned [Member] First-Lien RMBS Reserves [Member]	Mar. 31, 2012 Bankruptcy [Member] First-Lien RMBS Reserves [Member]	Aug. 31, 2012 Scenario, Forecast [Member]	Sep. 30, 2012 Scenario, Forecast [Member]	Feb. 28, 2013 Scenario, Forecast [Member] RMBS And HELOC And CES [Member]	Aug. 31, 2012 Scenario, Forecast [Member] First-Lien RMBS Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Charged-off loans recovery values		$ 0
Delinquency period charged off on transaction specific basis, days				90
Assumed roll rate for ninety plus day delinquent loans			95.00%
Assumed roll rate for loans							90.00%	90.00%	75.00%
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%
90+ day roll rate to loss set				90.00%
Period of elevated delinquency and loss for stress case, additional months												6
Addition to case basis reserves before considering potential recoveries			160,000,000
Percentage of loss after declining over a 24-month period						25.00%
Change in recoveries of actual and expected payments related to ineligible mortgages			$ 49,000,000