Loss And Loss Adjustment Expense Reserves (Loss And LAE Activity) (Narrative) (Detail) (USD $)	3 Months Ended		9 Months Ended					9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 U S Public Finance Insurance [Member]	Sep. 30, 2013 Abs Cdo Portfolio [Member]	Sep. 30, 2013 Insured Issues Designated As Classified List [Member] Variable Interest Entity Primary Beneficiary [Member] issue	Sep. 30, 2013 Rmbs And Heloc And Ces [Member]	Sep. 30, 2013 Rmbs And Heloc And Ces [Member] Ineligible Loan Recoveries [Member]	Sep. 30, 2013 Second Lien Residential Mortgage Backed Securities And Reserves [Member]	Sep. 30, 2013 Second Lien Residential Mortgage Backed Securities And Reserves [Member] Ineligible Loan Recoveries [Member]	Sep. 30, 2013 Financial Guarantee [Member]	Sep. 30, 2013 Financial Guarantee [Member] Variable Interest Entity Primary Beneficiary [Member]	Sep. 30, 2013 Loss And Lae Reserves [Member]	Dec. 31, 2012 Loss And Lae Reserves [Member]	Sep. 30, 2013 Recoveries On Unpaid Losses [Member]	Dec. 31, 2012 Recoveries On Unpaid Losses [Member]	Sep. 30, 2013 Insurance Loss Recoverable [Member]	Dec. 31, 2012 Insurance Loss Recoverable [Member]	Sep. 30, 2013 Insurance Loss Recoverable [Member] Classified [Member]	Dec. 31, 2012 Insurance Loss Recoverable [Member] Classified [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
ABS CDO exposure decrease since December 31,2007						96.00%
Aggregate ABS CDO Loss And LAE Reserves												$ 87,000,000	$ 196,000,000
Policyholder (Benefits) And Claims Incurred Net	98,000,000	171,000,000	92,000,000	330,000,000		(47,000,000)				(92,000,000)
Elimination Of Loss And LAE Expense As Result Of Consolidating VIE						39,000,000
Reduction of excess interest cash flows from securitizations								139,000,000
Losses and loss adjustment expense payments, net of reinsurance			372,000,000		134,000,000			166,000,000
Decrease in insurance loss recoverable related to paid losses			2,900,000,000
Reserves for expected future claim payments														1,000,000,000	1,200,000,000
Expected recoveries of future payments														326,000,000	332,000,000	326,000,000	332,000,000
Number of insured issues reviewed							11
Weighted average risk-free rate used to discount claim liability			2.11%
Total estimated insurance recoveries											1,100,000,000
Insurance claim loss recoverable																				737,000,000	3,610,000,000
Insurance loss recoverable											18,000,000							742,000,000	3,648,000,000	742,000,000	3,648,000,000
Loan repurchase commitments											1,100,000,000
Loss and loss adjustment expense collections, net of reinsurance			2,900,000,000					2,800,000,000
Losses and LAE related to actual and expected payments			205,000,000		86,000,000					85,000,000
Change in recoveries of actual and expected payments related to ineligible mortgages									$ 316,000,000