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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
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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 |  |  |  |  |  |  |  |  |  |

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