Loss And Loss Adjustment Expense Reserves (Loss And LAE Activity) (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended				9 Months Ended		12 Months Ended								9 Months Ended	45 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011 Second-Lien RMBS [Member]	Sep. 30, 2011 Ineligible Mortgage Loans [Member]	Sep. 30, 2011 RMBS And HELOC And CES [Member]	Sep. 30, 2011 Loss And LAE Reserves [Member]	Dec. 31, 2010 Loss And LAE Reserves [Member]	Sep. 30, 2011 Insurance Loss Recoverable [Member]	Sep. 30, 2011 Insurance Loss Recoverable [Member] Classified [Member]	Dec. 31, 2010 Insurance Loss Recoverable [Member] Classified [Member]	Sep. 30, 2011 Loan Repurchase Commitments [Member]	Sep. 30, 2011 Recoveries On Unpaid Losses [Member] Reviewed [Member] Classified [Member]	Sep. 30, 2011 Reviewed [Member] Classified [Member]	Sep. 30, 2011 Insured Issues Designated As Classified List [Member]	Sep. 30, 2011 ABS CDO Portfolio [Member]	Sep. 30, 2011 ABS CDO Portfolio [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
ABS CDO exposure decrease since December 31,2007																		80.00%
Aggregate ABS CDO loss and LAE reserves	$ 179,000,000		$ 179,000,000
ABS CDO aggregate loss and LAE benefit			484,000,000
Estimated insurance recoveries					2,800,000,000	2,800,000,000				1,900,000,000	(2,761,000,000)	(2,531,000,000)	938,000,000
Insurance loss recoverable					1,900,000,000						(2,770,000,000)	(2,531,000,000)					92,000,000	92,000,000
Estimated insured credit derivative impairments and LAE reserves, net of reinsurance and recoveries																	511,000,000
Losses and loss adjustment	190,000,000	(20,000,000)	204,000,000	122,000,000	35,000,000												51,000,000
Elimination of loss and LAE expense as a result of consolidating VIEs																	79,000,000
Recoveries of amounts from excess cash flows within securitizations							198,000,000
Excess interest cash flows from securitizations							76,000,000
Total paid losses, net of reinsurance and collections			634,000,000		463,000,000
Increase in insurance loss recoverable related to paid losses			231,000,000
Reserves for expected future claim payments								1,600,000,000	2,000,000,000
Expected recoveries of future payments								$ 687,000,000	$ 896,000,000
Number of insured issues reviewed															29	34
Number of insured issues reviewed with recorded recoveries														27
Weighted average risk-free rate used to discount claim liability			1.51%