Loss And Loss Adjustment Expense Reserves (RMBS Reserves) (Narrative) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance loss recoverable		$ 577	$ 533	$ 694
Schedule Of Insured Financial Obligations With Credit Deterioration Insured Contractual Payments Outstanding Principal	[1]	11,160	11,263
Policyholder (Benefits) And Claims Incurred Net		123	133	117
Contract claims on ineligible mortgage loans inception to date, incurred loss on transactions		424
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss and loss adjustment expense reserves		516	506	641
Expected recoveries of future payments		100	147	206
First Lien R M B S Reserves [Member] | Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss and loss adjustment expense reserves		277	263
First Lien R M B S Reserves [Member] | Variable Interest Entity Primary Beneficiary [Member] | Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss and loss adjustment expense reserves		5
Second Lien Rmbs And Heloc And Ces [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Addition to case basis reserves if losses remain at peak levels		28
Second Lien Rmbs And Heloc And Ces [Member] | Excess Spread [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance loss recoverable		382	496
Total excess spread recoveries		499	660
Expected recoveries of future payments		24	27
Second Lien Rmbs And Heloc And Ces [Member] | Excess Spread [Member] | Variable Interest Entity Primary Beneficiary [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance loss recoverable		87	132
Total excess spread recoveries		93	137
Expected recoveries of future payments		6	5
U S Public Finance Insurance [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss and loss adjustment expense reserves		45	45
Insurance loss recoverable		4	4
Policyholder (Benefits) And Claims Incurred Net		5	(10)	$ 105
U S Public Finance Insurance [Member] | General obligations
Loss And Loss Adjustment Expense Reserves [Line Items]
Schedule Of Insured Financial Obligations With Credit Deterioration Insured Contractual Payments Outstanding Principal		70,000	98,900
U S Public Finance Insurance [Member] | General obligations | Classified [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Schedule Of Insured Financial Obligations With Credit Deterioration Insured Contractual Payments Outstanding Principal		79	152
Second Lien R M B S Securitizations [Member] | Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss and loss adjustment expense reserves		51	70
Second Lien R M B S Securitizations [Member] | Variable Interest Entity Primary Beneficiary [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss and loss adjustment expense reserves		$ 16	$ 21

[1] Represents contractual principal and interest payments due by the issuer of the obligations insured by MBIA.